This region of Earth is one of the most seismically active in the past decade plus. This morning, as I was preparing for work, I got an email notifying me of an earthquake with a magnitude M = 7.5 located near New Ireland, Papua New Guinea.
https://earthquake.usgs.gov/earthquakes/eventpage/us70003kyy/executive
There are every type of plate boundary fault in this region. There are subduction zones, such as that forms the New Britain and San Cristobal trenches. There are transform faults, such as that responsible for the M 7.5 temblor. There are also spreading ridges, such as the one that forms the Manus Basin to the northwest of today’s quake.
I interpret this M 7.5 earthquake to be a left-lateral strike slip earthquake based on (1) the USGS mechanism (moment tensor), (2) our knowledge of the faulting in the region, and (3) historic analogue earthquake examples. There was an earthquake on a subparallel strike-slip fault on 8 March 2018 (here is the earthquake report for that event). Also in that report, I discuss an earthquake from November 2000 that had a magnitude M = 8.0.
After my work on the 28 September 2018 Donggala-Palu earthquake, landslides, and tsunami, I am open minded about the possibility of strike-slip earthquakes as having tsunamigenic potential. There are actually many examples of strike-slip earthquakes causing tsunami, including the 1999 Izmit, 2012 Wharton Basin, and the 2000 New Ireland earthquake too! (see Geist and Parsons, 2005 for more about the small 2000 tsunami.) There was initially a tsunami notification from tsunami.gov about the possibility of a tsunami. Here is a great website where I usually visit when I am looking for tsunami records on tide gage data. This is the closest gage to the quake, but it is not located optimally to record a small tsunami as might have been generated today (I checked).
The Weitin fault is a very active fault, with a slip rate of about 130 mm/yr (Tregoning et al, 1999, 2005). For a comparison, the San Andreas fault has a slip rate of about 25-35 mm/year. Here is a great treatise on the SAF.
There are also examples of earthquake triggering in this region. For example, the 2000.11.16 M 8.0 strike-slip earthquake triggered the 2000.11.16 M 7.8 thrust fault earthquake. It is not unreasonable to consider it possible that there may be triggered earthquakes from this M 7.5 earthquake. Of course, we won’t know until it happens because nobody has the capability to predict earthquakes (regardless of what the charlatans may claim).
The USGS has a variety of products associated with their earthquake pages. I use many of these products in these earthquake reports, so I especially appreciate them. One of the recently added products is a landslide and a liquefaction probability model output. Based on our knowledge of how earthquake release energy, and our knowledge of how earth materials respond to this energy release, people have developed models that allow us to estimate the possibility any given region may experience landslides or liquefaction. I spent some time discussing this in the 28 Sept. 2018 Donggala-Palu earthquake report here.
Below is my interpretive poster for this earthquake
I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 3.0 in one version.
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
- I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
- I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
- I include the slab 2.0 contours plotted (Hayes, 2018), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault.
- In the map below, I include a transparent overlay of the magnetic anomaly data from EMAG2 (Meyer et al., 2017). As oceanic crust is formed, it inherits the magnetic field at the time. At different points through time, the magnetic polarity (north vs. south) flips, the North Pole becomes the South Pole. These changes in polarity can be seen when measuring the magnetic field above oceanic plates. This is one of the fundamental evidences for plate spreading at oceanic spreading ridges (like the Gorda rise).
- Regions with magnetic fields aligned like today’s magnetic polarity are colored red in the EMAG2 data, while reversed polarity regions are colored blue. Regions of intermediate magnetic field are colored light purple.
- We can see the roughly east-west trends of these red and blue stripes in the Woodlark Basin. These lines are parallel to the ocean spreading ridges from where they were formed. The stripes disappear at the subduction zone because the oceanic crust with these anomalies is diving deep beneath the upper plate, so the magnetic anomalies from the overlying plate mask the evidence for the lower plate.
Magnetic Anomalies
- In the lower left corner is a figure from Oregon State University (Geology). This shows a cartoon view of the tectonic plates in the region. Note the subduction zone where the Solomon Sea late dives beneath the South Bismarck and Pacific plates. Of particular interest today is the transform (strike-slip) plate boundary between the North and South Bismarck plates.
- In the upper left corner are two more detailed tectonic maps from Holm et al. (2019). The upper panel shows the plate boundary faults (active subduction zones are symbolized with dark triangles, fossil subd. zones are shown as open triangles). I plate a blue star int eh location of today’s earthquake (as for all inset figures). The lower panel shows the source of volcanic rocks as they have been derived from different subducted oceanic crust and overlying mantle. The geochemistry of these volcanic rocks helps us learn about the tectonic history of this complicated region.
- The figure in the lower right corner (Holm et al., 2019) shows the current configuration of the different plate boundary faults. Note the left lateral strike-slip relative motion on the (labeled here) Bismarck Sea fault. When this fault crosses New Ireland, it splays into a series of different faults. The most active fault is the Weitin fault.
- The figure in the upper right corner has lots of information, including cross sections showing the subduction zones (Holm et al., 2016). The oceanic crust created by spreading centers is highlighted for the Woodlark Basin, as well as the Manus Basin northwest of today’s M 7.5 earthquake. The cross section A-B shows these spreading centers.
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
- Here is the map with a month’s seismicity plotted. This map includes magnetic anomaly data.
- Here is the map with a century’s seismicity plotted for magnitudes M ≥ 7.5. Because of the complexity of this figure, the magnetic anomaly data are not included.
M 7.5 Landslide and Liquefaction Models
There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:
FOS = Resisting Force / Driving Force
When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.
Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.
Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.
Here is an excellent educational video from IRIS and a variety of organizations. The video helps us learn about how earthquake intensity gets smaller with distance from an earthquake. The concept of liquefaction is reviewed and we learn how different types of bedrock and underlying earth materials can affect the severity of ground shaking in a given location. The intensity map above is based on a model that relates intensity with distance to the earthquake, but does not incorporate changes in material properties as the video below mentions is an important factor that can increase intensity in places.
If we look at the map at the top of this report, we might imagine that because the areas close to the fault shake more strongly, there may be more landslides in those areas. This is probably true at first order, but the variation in material properties and water content also control where landslides might occur.
There are landslide slope stability and liquefaction susceptibility models based on empirical data from past earthquakes. The USGS has recently incorporated these types of analyses into their earthquake event pages. More about these USGS models can be found on this page.
I prepared some maps that compare the USGS landslide and liquefaction probability maps.
- Here is the landslide probability map (Jessee et al., 2018). Below the poster I include the text from the USGS website that describes how this model is prepared. The topography and bathymetry come from the National Science Foundation funded GeoMapApp.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
- Here is the liquefaction probability (susceptibility) map (Zhu et al., 2017). Note that the regions of low slopes in the valleys and coastal plains are the areas with a high chance of experiencing liquefaction.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
Other Report Pages
Some Relevant Discussion and Figures
- Here is the generalized tectonic map of the region from Holm et al., 2015. I include the figure caption below as a blockquote.
- In earlier earthquake reports, I discussed seismicity from 2000-2015 here. The seismicity on the west of this region appears aligned with north-south shortening along the New Britain trench, while seismicity on the east of this region appears aligned with more east-west shortening. Here is a map that I put together where I show these two tectonic domains with the seismicity from this time period (today’s earthquakes are not plotted on this map, but one may see where they might plot).
- Here is the slab interpretation for the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.
- Here are the forward models for the slab in the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.
- Here is a map showing some detailed mapping of the Weitin fault (Lindley, 2006).
- This figure shows details of the regional tectonics (Holm et al., 2016). I include the figure caption below as a blockquote.
- Here is a larger scale map showing lineaments (thin black lines) which represent structures formed at the spreading ridges (Lindley, 2006). These spreading ridges are perpendicular to the Weitin and sister transform faults (like the Sapom fault).
- The interpretive poster above shows the 2007 M 8.1 tsunamigenic subduction zone earthquake. I presented information about this earthquake in a report from 22 Jan. 2017 here. Below are some of the interpretive posters from that report that show excellent examples of subduction zone earthquakes along the San Cristobal trench.
- Here is my interpretive poster from the 12/17 M 7.9 Bougainville Earthquake, possibly (probably) related to today’s M 7.9 earthquake. This is my Earthquake Report for the 12/17 earthquake.
- For a comparison, here is an earthquake that happened along the New Britain subduction zone. Note how the orientation of the earthquake mechanism is aligned with the trench.
- Here is the map with a century’s seismicity plotted.
- Here are the maps from Holm et al. (2019) that show the sources of volcanic rocks in the region.
- This is a series of plate reconstructions from Holm et al. (2019), the final panel is in the interpretive poster above.
Tectonic setting and mineral deposits of eastern Papua New Guinea and Solomon Islands. The modern arc setting related to formation of the mineral deposits comprises, from west to east, the West Bismarck arc, the New Britain arc, the Tabar-Lihir-Tanga-Feni Chain and the Solomon arc, associated with north-dipping subduction/underthrusting at the Ramu-Markham fault zone, New Britain trench and San Cristobal trench respectively. Arrows denote plate motion direction of the Australian and Pacific plates. Filled triangles denote active subduction. Outlined triangles denote slow or extinct subduction. NBP: North Bismarck plate; SBP: South Bismarck plate; AT: Adelbert Terrane; FT: Finisterre Terrane; RMF: Ramu-Markham fault zone; NBT: New Britain trench.
3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.
Forward tectonic reconstruction of progressive arc collision and accretion of New Britain to the Papua New Guinea margin. (a) Schematic forward reconstruction of New Britain relative to Papua New Guinea assuming continued northward motion of the Australian plate and clockwise rotation of the South Bismarck plate. (b) Cross-sections illustrate a conceptual interpretation of collision between New Britain and Papua New Guinea.
Weitin Fault, Southern New Ireland, showing trace of fault, topography and evidence used by Hohnen (1978) to tentatively suggest sinistral fault movement (after Hohnen, 1978).
a) Present day tectonic features of the Papua New Guinea and Solomon Islands region as shown in plate reconstructions. Sea floor magnetic anomalies are shown for the Caroline plate (Gaina and Müller, 2007), Solomon Sea plate (Gaina and Müller, 2007) and Coral Sea (Weissel and Watts, 1979). Outline of the reconstructed Solomon Sea slab (SSP) and Vanuatu slab (VS)models are as indicated. b) Cross-sections related to the present day tectonic setting. Section locations are as indicated. Bismarck Sea fault (BSF); Feni Deep (FD); Louisiade Plateau
(LP); Manus Basin (MB); New Britain trench (NBT); North Bismarck microplate (NBP); North Solomon trench (NST); Ontong Java Plateau (OJP); Ramu-Markham fault (RMF); San Cristobal trench (SCT); Solomon Sea plate (SSP); South Bismarck microplate (SBP); Trobriand trough (TT); projected Vanuatu slab (VS); West Bismarck fault (WBF); West Torres Plateau (WTP); Woodlark Basin (WB).
Map showing onshore structures of the Gazelle Peninsula and New Ireland and those interpreted from SeaMARC II sidescan backscatter data in the Eastern Bismarck Sea. BSSL, Bismarck Sea Seismic Lineation (BSSL). SeaMARC II backscatter data from which lineations have been picked are from Taylor et al. (1991 a-c). Modified after Madsen and Lindley (1994).
Here is a visualization of the seismicity as presented by Dr. Steve Hicks.
Tectonic setting of Papua New Guinea and Solomon Islands. A) Regional plate boundaries and tectonic elements. Light grey shading illustrates bathymetry <2000m below sea level indicative of continental or arc crust, and oceanic plateaus. The New Guinea Orogen comprises rocks of the New Guinea Mobile Belt and the Papuan Fold and Thrust Belt; Adelbert Terrane (AT); Aure-Moresby trough (AMT); Bougainville Island (B); Bismarck Sea fault (BSF); Bundi fault zone (BFZ); Choiseul Island (C); Feni Deep (FD); Finisterre Terrane (FT); Guadalcanal Island (G); Gazelle Peninsula (GP); Kia-Kaipito-Korigole fault zone (KKKF); Lagaip fault zone (LFZ); Malaita Island (M); Manus Island (MI); New Britain (NB); New Georgia Islands (NG); New Guinea Mobile Belt (NGMB); New Ireland (NI); Papuan Fold and Thrust Belt (PFTB); Ramu-Markham fault (RMF); Santa Isabel Island (SI); Sepik arc (SA); Weitin Fault (WF); West Bismarck fault (WBF); Willaumez-Manus Rise (WMR). Arrows indicate rate and direction of plate motion of the Australian and Pacific plates (MORVEL, DeMets et al., 2010); B) Pliocene-Quaternary volcanic centres and magmatic arcs related to this study. Figure modified from Holm et al. (2016). Subduction zone symbols with filled pattern denote active subduction; empty symbols denote extinct subduction zone or negligible convergence.
Selected tectonic reconstructions and mineral deposit formation for key areas and times within the eastern Papua New Guinea and Solomon Islands region. A) Formation of the Panguna and Fauro Island Deposits above the interpreted subducted margin of the Solomon Sea plate-Woodlark Basin, and Mase deposit above the subducting Woodlark spreading center; B) Formation of the New Georgia deposits above the subducting Woodlark spreading center, and Guadalcanal deposits above the subducting margin of the Woodlark Basin; C) Formation of the Solwara deposits related to transtension along the Bismarck Sea fault above the subducting Solomon Sea plate, and deposits of the Tabar- Lihir-Tanga-Feni island arc chain related to upper plate extension (normal faulting indicated by hatched linework between New Ireland and Bougainville), while the Ladolam deposit forms above a tear in the subducting slab. Interpreted Solomon Sea slab (light blue shaded area for present-day) is from Holm and Richards (2013); the reconstructed surface extent or indicative trend of slab structure is indicated by the dashed red lines. Green regions denote the present-day landmass using modern coastlines; grey regions are indicative of crustal extent using the 2000m bathymetric contour. The reconstruction is presented here relative to the global moving hotspot reference frame, please see the reconstruction files in the supplementary material for specific reference frames.
Geologic Fundamentals
- For more on the graphical representation of moment tensors and focal mechanisms, check this IRIS video out:
- Here is a fantastic infographic from Frisch et al. (2011). This figure shows some examples of earthquakes in different plate tectonic settings, and what their fault plane solutions are. There is a cross section showing these focal mechanisms for a thrust or reverse earthquake. The upper right corner includes my favorite figure of all time. This shows the first motion (up or down) for each of the four quadrants. This figure also shows how the amplitude of the seismic waves are greatest (generally) in the middle of the quadrant and decrease to zero at the nodal planes (the boundary of each quadrant).
- Here is another way to look at these beach balls.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj
— AK Earthquake Center (@AKearthquake) August 15, 2018
- There are three types of earthquakes, strike-slip, compressional (reverse or thrust, depending upon the dip of the fault), and extensional (normal). Here is are some animations of these three types of earthquake faults. The following three animations are from IRIS.
Strike Slip:
Compressional:
Extensional:
- This is an image from the USGS that shows how, when an oceanic plate moves over a hotspot, the volcanoes formed over the hotspot form a series of volcanoes that increase in age in the direction of plate motion. The presumption is that the hotspot is stable and stays in one location. Torsvik et al. (2017) use various methods to evaluate why this is a false presumption for the Hawaii Hotspot.
- Here is a map from Torsvik et al. (2017) that shows the age of volcanic rocks at different locations along the Hawaii-Emperor Seamount Chain.
- Here is a great tweet that discusses the different parts of a seismogram and how the internal structures of the Earth help control seismic waves as they propagate in the Earth.
A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy
— Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
- 2019.05.14 M 7.5 New Ireland
- 2019.05.06 M 7.2 Papua New Guinea
- 2018.12.05 M 7.5 New Caledonia
- 2018.10.10 M 7.0 New Britain, PNG
- 2018.09.09 M 6.9 Kermadec
- 2018.08.29 M 7.1 Loyalty Islands
- 2018.08.18 M 8.2 Fiji
- 2018.03.26 M 6.9 New Britain
- 2018.03.26 M 6.6 New Britain
- 2018.03.08 M 6.8 New Ireland
- 2018.02.25 M 7.5 Papua New Guinea
- 2018.02.26 M 7.5 Papua New Guinea Update #1
- 2017.11.19 M 7.0 Loyalty Islands Update #1
- 2017.11.07 M 6.5 Papua New Guinea
- 2017.11.04 M 6.8 Tonga
- 2017.10.31 M 6.8 Loyalty Islands
- 2017.08.27 M 6.4 N. Bismarck plate
- 2017.05.09 M 6.8 Vanuatu
- 2017.03.19 M 6.0 Solomon Islands
- 2017.03.05 M 6.5 New Britain
- 2017.01.22 M 7.9 Bougainville
- 2017.01.03 M 6.9 Fiji
- 2016.12.17 M 7.9 Bougainville
- 2016.12.08 M 7.8 Solomons
- 2016.10.17 M 6.9 New Britain
- 2016.10.15 M 6.4 South Bismarck Sea
- 2016.09.14 M 6.0 Solomon Islands
- 2016.08.31 M 6.7 New Britain
- 2016.08.12 M 7.2 New Hebrides Update #2
- 2016.08.12 M 7.2 New Hebrides Update #1
- 2016.08.12 M 7.2 New Hebrides
- 2016.04.06 M 6.9 Vanuatu Update #1
- 2016.04.03 M 6.9 Vanuatu
- 2015.03.30 M 7.5 New Britain (Update #5)
- 2015.03.30 M 7.5 New Britain (Update #4)
- 2015.03.29 M 7.5 New Britain (Update #3)
- 2015.03.29 M 7.5 New Britain (Update #2)
- 2015.03.29 M 7.5 New Britain (Update #1)
- 2015.03.29 M 7.5 New Britain
- 2015.11.18 M 6.8 Solomon Islands
- 2015.05.24 M 6.8, 6.8, 6.9 Santa Cruz Islands
- 2015.05.05 M 7.5 New Britain
New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports
General Overview
Earthquake Reports
Social Media
- Baldwin, S.L., Monteleone, B.D., Webb, L.E., Fitzgerald, P.G., Grove, M., and Hill, E.J., 2004. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea in Nature, v. 431, p/ 263-267, doi:10.1038/nature02846.
- Baldwin, S.L., Fitzgerald, P.G., and Webb, L.E., 2012. Tectonics of the New Guinea Region, Annu. Rev. Earth Planet. Sci., v. 40, pp. 495-520.
- Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren, P.Q., and McMahon, T.P., 2005, Collisional delamination in New Guinea: The geotectonics of subducting slab breakoff: Geological Society of America Special Paper 400, 51 p., doi: 10.1130/2005.2400.
- Hamilton, W.B., 1979. Tectonics of the Indonesian Region, USGS Professional Paper 1078.
- Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
- Geist, E. L., and T. Parsons (2005), Triggering of tsunamigenic aftershocks from large strike-slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence, Geochem. Geophys. Geosyst., 6, Q10005, https://doi.org/10.1029/2005GC000935.
- Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
- Highland, L.M., and Bobrowsky, P., 2008. The landslide handbook—A guide to understanding landslides, Reston, Virginia, U.S. Geological Survey Circular 1325, 129 p.
- Holm, R. and Richards, S.W., 2013. A re-evaluation of arc-continent collision and along-arc variation in the Bismarck Sea region, Papua New Guinea in Australian Journal of Earth Sciences, v. 60, p. 605-619.
- Holm, R.J., Richards, S.W., Rosenbaum, G., and Spandler, C., 2015. Disparate Tectonic Settings for Mineralisation in an Active Arc, Eastern Papua New Guinea and the Solomon Islands in proceedings from PACRIM 2015 Congress, Hong Kong ,18-21 March, 2015, pp. 7.
- Holm, R.J., Rosenbaum, G., Richards, S.W., 2016. Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands: Microplate tectonics in a convergent plate boundary setting in Eartth Science Reviews, v. 156, p. 66-81.
- Holm, R.J., Tapster, S., Jelsma, H.A., Rosenbaum, G., and Mark, D.F., 2019. Tectonic evolution and copper-gold metallogenesis of the Papua New Guinea and Solomon Islands region in Ore Geology Reviews, v. 104, p. 208-226, https://doi.org/10.1016/j.oregeorev.2018.11.007
- Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
- Johnson, R.W., 1976, Late Cainozoic volcanism and plate tectonics at the southern margin of the Bismarck Sea, Papua New Guinea, in Johnson, R.W., ed., 1976, Volcanism in Australia: Amsterdam, Elsevier, p. 101-116
- Keefer, D.K., 1984. Landslides Caused by Earthquakes in GSA Bulletin, v. 95, p. 406-421
- Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
- Lindley, I.D., 2006. Extensional and vertical tectonics in the New Guinea islands: implications for island arc evolution in Annals of Geophysics, suppl to v. 49, no. 1, p. 403-426
- Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
- Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
- Tregoning, P., Jackong, R.J., McQueen, H., Lambeck, K., Stevens, C., Little, R.P., Curley, R., and Rosa, R., 1999. Motion of the South Bismarck Plate, Papua New Guinea in GRL, v. 26, no. 23, p. 3517-3520
- Tregoning, P., McQueen, H., Lambeck, K., Jackson, R. Little, T., Saunders, S., and Rosa, R., 2000. Present-day crustal motion in Papua New Guinea, Earth Planets and Space, v. 52, pp. 727-730.
- Tregoning, P., Sambridge, M., McQueen, H., Toulin, S., and Nicholson, T., 2005. Motion of the South Bismarck Plate, Papua New Guinea in GJI, v. 160, p. 1103-111, https://doi.org/10.111/j.1365-246X.2005.02567.x
- USGS, 2004. Landslide Types and Processes, U.S. Geological Survey Fact Sheet 2004-3072
- Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, doi: 0.1785/0120160198
References:
Return to the Earthquake Reports page.
There was just now an earthquake beneath Panamá. The major plate boundary in the region is a subduction zone (convergent plate boundary) where the Cocos and Nazca plates dive northwards beneath the Caribbean plate forming the Middle America trench (MAT). I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 3.0 in one version.
Gala´pagos Islands and hotspot tracks (Cocos, Coiba, Malpelo, and Carnegie Ridges), igneous complexes in Central America with Gala´pagos geochemical affinities, and western portion of Caribbean plate. Is. is Island, S.C. is spreading
Map of southern Central America (dark shading) and the Panama microplate (pale shading). Darien is picked out in pale shading. Dashed lines with teeth mark zones of convergence; zippered line is Panama-Colombia suture. Very heavy dashed line marks location of Neogene volcanic arc; black circles mark Paleogene-Eocene volcanic arc. NPDB – North Panama deformed belt; SPDB – South Panama deformed belt; PFZ – Panama fracture zone. Principal Neogene sedimentary basins located by striped ovals.
Crustal structure between Malpelo and Panama, showing 1965 to 1975 epicenters (defining present plate boundaries), magnetic anomalies, tracks of profiles shown in Figures 6 and 8, and locations of sampling sites.
Magnetic anomalies between Malpelo and Carnegie Ridges, numbered according to time scales listed in caption of Figure 2. Note anomaly 5 to 5B sequence along long 81°W, mirrored around extinct Malpelo rift spreading center at lat 1°40’N. Magnetic anomalies on western (Costa Rica rift) segment are from Hey and others (1977). Tracks are labeled for Conrad 11.11 (CON 11) Yaloc 69 (Y 69), Iguana 3, Cocotow 2 (CCTW 2), Cocotow 3 (CCTW 3), F. Drake 3 (FD 3), and some lines of Oceanographer 70 (OC 70). Unlabeled profiles on Costa Rica rift are from Oceanographer 69; those on Malpelo rift are from Oceanographer 70.
Profile of Cocotow 3 traverse between Malpelo and Carnegie Ridges (see Fig. 4 for location). Synthetic magnetic profile was generated using reversal time scale discussed in Figure 2 caption, spreading rates indicated at top of this figure, magnetization of 4 A/m, and magnetized layer that is 500 m thick and has an upper surface that coincides with basement relief. Note that anomaly match is poor
Tectonic reconstructions tracing inferred history of eastern Panama Basin. (A) Middle Oligocene: Farallon plate interacting with Caribbean and South American plates, just before splitting into Nazca and Cocos plates. (B) Middle Miocene: Malpelo and Carnegie Ridges are being formed by hot spot centered on Nazca plate near axis of Nazca-Cocos spreading and are being continuously separated by spreading at boundary. (C) Late Miocene: slowdown of spreading on Malpelo rift, rejuvenation of fracture zone at long 83°W, and cessation of subduction at Panama Trench. (D) Early Pliocene: continued northward migration of Cocos Ridge, stagnation of Malpelo Ridge, and uplift of Coiba Ridge near Nazca-Cocos-Caribbean triple junction. (E) Pleistocene: Cocos and Carnegie Ridges have just arrived at Middle America and Ecuador Trenches, and triple junction has jumped west from Coiba to Panama fracture zone.
Overview of the eastern Panama Basin (modified from Meschede et al., 1998). Numbers indicate the ages of oceanic crust. The distribution of extinct spreading systems is from Meschede et al. (1998). CNS = Cocos-Nazca spreading system. RSB = rough/smooth boundary.
Map depicting lhe southwestern Panama continental manin and lhe Panama-Coiba Fracture Zone wilh some of its characteristic focal mechanisms.
Interpretation of the pattern of crustal isochrons (Hardy 1991; Lonsdale 2005) and plate boundaries in the Panama Basin (modified from Lonsdale 2005). Earthquakes (black dots) and fault plane solution are from the Harvard University archive of centroid-moment tensor solutions. Plain lines are active spreading axis and transform faults: Costa Rica Rift (CRR) and Panama Fracture Zone (PFZ). Dashed and dotted lines are fossil spreading axis and transform faults: Buenaventura Rift (BR), Malpelo Rift (MR), Coiba Fracture Zone (CFZ) and Yaquina Graben. Possible spreading activity along Sandra Rift (SR) is still in discussion.
(a) Digital elevation model of the plate tectonic setting surrounding the Cordillera de Talamanca (CT), southern Costa Rica and Cordillera Central (CC), western Panama. Tectonic plates shown are the Cocos plate (CO), Nazca plate (NZ), Caribbean plate (CA), Panama microplate (PM), with plate velocities relative to a fixed CA plate [Bird, 2003; DeMets et al., 1990; DeMets, 2001; Jin and Zhu, 2004; Kellogg and Vega, 1995]. MAT, Middle America Trench; EPR, East Pacific Rise; CNS-2, Cocos-Nazca-Spreading; PTJ, Panama Triple Junction; PFZ, Panama Fracture Zone; BFZ, Balboa Fracture Zone; CFZ, Coiba Fracture Zone; NP, Nicoya Peninsula; AG, Aguacate Range; OP, Osa Peninsula; BP, Burica Peninsula; FCTB, Fila Costeña Thrust Belt; NPDB, North Panama Deformed Belt; TV, Tisingal Volcano; IV, Irazú volcano; BV, Barú volcano; YV, La Yeguada volcano; EV, El Valle volcano. Bathymetric data supplied by ETOPO1 combined from Amante and Eakins [2009], Smith and Sandwell [1997], and Ranero et al. [2003]. Topography supplied by CGIR-CSI based on NASA’s SRTM4 data set. White triangles indicate active volcanoes. Yellow dashed lines indicate on-land projection of Cocos Ridge boundaries. (b) Inset showing location of Figure 1a based on ETOPO1 data. SA refers to the South American plate. (c) Velocity triangle for Panama Triple Junction. CR represents the axis of the Cocos Ridge. Red lines denote the PM-CO and PM-NZ vectors, respectively. Numbers shown are in mm/yr.
Map of southern Central America, showing plate tectonic setting surrounding the Panama triple junction (PTJ) and Barú Volcano based on a stable Caribbean plate (DeMets et al., 1990; Kellogg and Vega, 1995; DeMets, 2001; Bird, 2003). MAT—Middle America Trench; CO—Cocos plate; NZ—Nazca plate; CA— Caribbean plate; PM—Panama micro plate; PTJ—Panama triple junction; PFZ—Panama fracture zone; BFZ—Balboa fracture zone; CFZ—Coiba fracture zone; TV—Tisingal Volcano; OP—Osa Peninsula; BP—Burica Peninsula; VG— Valle General. Elevations are based on National Aeronautics and Space Administration’s (NASA) SRTM v4 imagery. Bathymetry is combined from ETOPO1 and Ranero et al. (2003). Thrusts and shortening estimates outlined for Fila Costeña thrust belt are combined from Sitchler et al. (2007), Fisher et al. (2004), and Morell et al. (2008). Fault traces on Burica Peninsula are from Morell et al. (2011a) and back arc is from Brandes et al. (2007). Contour interval for bathymetry is 250 m.
Map of normalized steepness (ksn) values calculated over a 0.5 km window for drainage basins >107 m2 and excluding valley bottoms for Cordillera de Talamanca and western Cordillera Central. Numbers in northeastern flank of Talamanca correspond to knickpoint numbers shown in Table 2. The locations of longitudinal profiles in Figure 7 are marked as A, B and C, respectively. Faults shown in the Fila Costeña are based on Fisher et al. [2004], Morell et al. [2008], and Sitchler et al. [2007]. Faults drawn in the Limón back arc are approximated from topographic lineaments. Location shown in Figure 1. Base map sourced from DEM draped over slope map derived from SRTM data set. Inset in upper right is simplified geologic map for Cordillera de Talamanca region based on Denyer and Alvarado [2007].
Simplified geologic map of the southeast Fila Costeña Thrust Belt in the inner forearc of Costa Rica and western Panama (see Fig. 1 for location). Combined data from Sitchler et al. (in press) and this study, revised after Kolarsky and Mann (1995) and Mora (1979). Although the thrust belt continues to the northwest, we focus on the southeast termination. Black boxes indicate location of Figs. 3 and 5. OPFZ = On-land projection of the Panama Fracture Zone. Geology is draped on 90-m DEM supplied by NASA’s SRTM-3 dataset. Stratigraphic column modified after Sitchler et al. (in press), Phillips (1983) and Fisher et al. (2004). Inset A shows shaded DEM of area in white dotted box denoting scarps visible for right-lateral faults A and B based on SRTM-3 dataset.
Bedrock geologic map of the southeastern termination of the Fila Costeña Thrust Belt showing strike and dip measurements within thrust sheets that dip to the northeast. The southeastern termination of the thrust belt roughly coincides with the on-land projection of the Panama Fracture Zone (OPFZ, red dashed line), which is migrating to the southeast with the Panama Triple Junction. F1, F2, F3, F4, and F5 refer to thrust faults 1, 2, 3, 4 and 5, respectively. Cross-sections show locations of balanced cross-sections in Fig. 4. All fault traces and contacts are approximated. Inset index map shows figure location in red box relative to the on-land projection of the Panama Fracture Zone.
Digital elevation model [Smith and Sandwell, 1997; Amante and Eakins, 2009] showing Panama Basin and seafloor magnetic anomaly data surrounding the southern Central America subduction zone [Lonsdale and Klitgord, 1978; Wilson and Hey, 1995; Barckhausen et al., 2001; Lonsdale, 2005] based on chron time scale of Cande and Kent [1995]. The 22000 m contour is shown for prominent bathymetric features in the region, including Malpelo Ridge (MaR) and Coiba Ridge (CoR). BFZ, Balboa Fracture Zone; CFZ, Coiba Fracture Zone; CNS, Cocos-Nazca spreading center; COL, Colombia; CR, Costa Rica; EC, Ecuador; GHS, Galapagos hot spot; MR, Malpelo Rift; MAT, Middle America Trench; MoR, Morgan Rift; NI, Nicaragua; PA, Panama; PFZ, Panama Fracture Zone; SR, Sandra Rift; YG, Yaquina Graben. Inset: Present day plate boundaries of Cocos (CO), Nazca (NZ), Caribbean (CA), and South American (SA) plates. East Pacific Rise (EPR) and Cocos-Nazca Spreading Center (CNS) are also shown.
Plate reconstruction models for the Cocos (CO) and Nazca (NZ) plates relative to the Caribbean plate from 4 Ma to recent. BFZ, Balboa Fracture Zone; CaR, Carnegie Ridge; CFZ, Coiba Fracture Zone; CNS, crust derived from the Cocos-Nazca spreading center; CocR, Cocos Ridge; CoR, Coiba Ridge; CR, Costa Rica; EPR, crust derived from the East Pacific Rise; GH, Galapagos hot spot; MaR, Malpelo Ridge; MoR, Morgan Rift; MR, Malpelo Rift; PA, Panama; PFZ, Panama Fracture Zone; PTJ, Panama Triple Junction; RSB, rough-smooth boundary; SMD, seamount domain; SR, Sandra Ridge; YG, Yaquina Graben.
Plate reconstruction models for the Cocos and Nazca plates relative to the Caribbean plate from 6 to 10 Ma. CaR, Carnegie Ridge; CFZ, Coiba Fracture Zone; CNS, crust derived from the Cocos-Nazca spreading center; CocR, Cocos Ridge; CR, Costa Rica; EPR, crust derived from the East Pacific Rise; GH, Galapagos hot spot; MaR, Malpelo Ridge; MR, Malpelo Rift; PA, Panama; PFZ, Panama Fracture Zone; PTJ, Panama Triple Junction; SMD, seamount domain, SR, Sandra Ridge; YG, Yaquina Graben.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Mw=6.0, PANAMA-COSTA RICA BORDER REGION (Depth: 19 km), 2019/05/12 19:24:52 UTC – Full details here: https://t.co/cFrxlyVq2B pic.twitter.com/lJjmebILn7 — Earthquakes (@geoscope_ipgp) May 12, 2019 strong #earthquake in #Costa #Rica, also felt in #Panama @ShakingEarth pic.twitter.com/UDHCy9YDct — CATnews | Andreas M. Schäfer (@CATnewsDE) May 12, 2019 #Update: Video of beaches and the coast line in #CostaRica shows the 6,5M earthquake, making cracks and shaking layers upon layers of sand. And where the most damage is expected to be in #Panama. pic.twitter.com/gfzLK8YE2t — Sotiri Dimpinoudis ❁ (@sotiridi) May 12, 2019 EARTHQUAKE IN PANAMA: Some damages reported in Chiriqui region. #Panama #Earthquake #Temblor pic.twitter.com/fymkt7q9Hu — Earthquakes World (@Terremoti7) May 12, 2019 #panama earthquake aftermath. pic.twitter.com/YuGHI6LrZC — Shan Nayak (@ShanNayakk) May 12, 2019 Map of historical seismicity in the area around today's M6.1 Panama – Costa Rica border earthquake, an area of significant crustal strike-slip activity, in addition to a subduction zone pic.twitter.com/oTnnjv3ACj — Jascha Polet (@CPPGeophysics) May 13, 2019
Today is the anniversary of the 18 April 1906 San Francisco Earthquake. There are few direct observations (e.g. from seismometers or other instruments) from this earthquake, so our knowledge of how strong the ground shook during the earthquake are limited to indirect measurements. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1900-2018 with magnitudes M ≥ 5.5.
Fence half a mile northwest of Woodville (east of Point Reyes), offset by approximately 2.6 m of right-lateral strike-slip motion on the San Andreas fault in the 1906 San Francisco earthquake (U.S. Geological Survey Photographic Library, Gilbert, G. K. 2845).
ShakeMap for the 1906 San Francisco earthquake based on the Boatwright and Bundock (2005) intensities (processed 18 October 2005). Open circles identify the intensity sites used to construct the ShakeMap.
Spread failures on the banks of the Eel River near Port Kenyon in 1906. Photo E. Garrett, courtesy of Peter Palmquist.
Geologic sketch map of the northern Coast Ranges, central California, showing faults with Quaternary activity and basin deposits in northern section of the San Andreas fault system. Fault patterns are generalized, and only major faults are shown. Several Quaternary basins are fault bounded and aligned parallel to strike-slip faults, a relation most apparent along the Hayward-Rodgers Creek-Maacama fault trend.
EVOLUTION OF THE SAN ANDREAS FAULT.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Here I summarize Earth’s significant seismicity for 2018. I limit this summary to earthquakes with magnitude greater than or equal to M 6.5. I am sure that there is a possibility that your favorite earthquake is not included in this review. Happy New Year. One year of #earthquakes recorded by @INGVterremoti in Italy. About 2500 events with magnitude equal or larger than M2, about seven per day. Data source https://t.co/g1RvR2A989) #Italia #terremoto #Italy #earthquake pic.twitter.com/ft8GAsFjKA — iunio iervolino (@iuniervo) December 31, 2018 Earthquakes of 2018: a quick post summarising global seismic activity last year (i.e., the figures I showed you yesterday). https://t.co/ahdwpf1OFv pic.twitter.com/S438okD8QQ — Chris Rowan (@Allochthonous) January 1, 2019 Global #earthquakes by Magnitude (M5+) by year (2000-18), showing remarkable consistency from geologic forcing. Whereas patterns are understood, they do not permit short-term, local predictions; instead, be informed and be prepared. #geohazards @IRIS_EPO @USGS pic.twitter.com/BmtXhhUvWF — Ben van der Pluijm 🌎 (@vdpluijm) January 2, 2019 The pattern of shallow earthquakes (depth < 33 km) is typical, with much of the country susceptible to regular shallow seismicity, with lower rates in Northland/Auckland and southeast Otago. pic.twitter.com/3jip8Lyje9 — John Ristau 🇨🇦 🇳🇿 (@SinistralSeismo) January 3, 2019
Just a couple hours ago there was an earthquake along the Swan fault, which is the transform plate boundary between the North America and Caribbean plates. The Cayman trough (CT) is a region of oceanic crust, formed at the Mid-Cayman Rise (MCR) oceanic spreading center. To the west of the MCR the CT is bound by the left-lateral strike-slip Swan fault. To the east of the MCR, the CT is bound on the north by the Oriente fault. We had a damaging and (sadly) deadly earthquake in southern Peru in the last 24 hours. This is an earthquake, with magnitude M 7.1, that is associated with the subduction zone forming the Peru-Chile trench (PCT). The Nazca plate (NP) is subducting beneath the South America plate (SAP). There are lots of geologic structures on the Nazca plate that tend to affect how the subduction zone responds during earthquakes (e.g. segmentation). This earthquake appears to be located along a reactivated fracture zone in the GA. There have only been a couple earthquakes in this region in the past century, one an M 6.0 to the east (though this M 6.0 was a thrust earthquake). The Gulf of Alaska shear zone is even further to the east and has a more active historic fault history (a pair of earthquakes in 1987-1988). The magnetic anomalies (formed when the Earth’s magnetic polarity flips) reflect a ~north-south oriented spreading ridge (the anomalies are oriented north-south in the region of today’s earthquake). There is a right-lateral offset of these magnetic anomalies located near the M 7.9 epicenter. Interesting that this right-lateral strike-slip fault (?) is also located at the intersection of the Gulf of Alaska shear zone and the 1988 M 7.8 earthquake (probably just a coincidence?). However, the 1988 M 7.8 earthquake fault plane solution can be interpreted for both fault planes (it is probably on the GA shear zone, but I don’t think that we can really tell). As a reminder, if the M 7.9 earthquake fault is E-W oriented, it would be left-lateral. The offset magnetic anomalies show right-lateral offset across these fracture zones. This was perhaps the main reason why I thought that the main fault was not E-W, but N-S. After a day’s worth of aftershocks, the seismicity may reveal some north-south trends. But, as a drama student in 7th grade (1977), my drama teacher (Ms. Naichbor, rest in peace) asked our class to go stand up on stage. We all stood in a line and she mentioned that this is social behavior, that people tend to stand in lines (and to avoid doing this while on stage). Later, when in college, professors often commented about how people tend to seek linear trends in data (lines). I actually see 3-4 N-S trends and ~2 E-W trends in the seismicity data. There was just now an earthquake in Oaxaca, Mexico between the other large earthquakes from last 2017.09.08 (M 8.1) and 2017.09.08 (M 7.1). There has already been a M 5.8 aftershock.Here is the USGS website for today’s M 7.2 earthquake. This morning (local time in California) there was an earthquake in Papua New Guinea with, unfortunately, a high likelihood of having a good number of casualties. I was working on a project, so could not immediately begin work on this report. We had an M 6.8 earthquake near a transform micro-plate boundary fault system north of New Ireland, Papua New Guinea today. Here is the USGS website for this earthquake. The New Britain region is one of the more active regions in the world. See a list of earthquake reports for this region at the bottom of this page, above the reference list. Well, those earthquakes from earlier, one a foreshock to a later one, were foreshocks to an earthquake today! Here is my report from a couple days ago. The M 6.6 and M 6.3 straddle today’s earthquake and all have similar hypocentral depths. A couple days ago there was a deep focus earthquake in the downgoing Nazca plate deep beneath Bolivia. This earthquake has an hypocentral depth of 562 km (~350 miles). There has been a swarm of earthquakes on the southeastern part of the big island, with USGS volcanologists hypothesizing about magma movement and suggesting that an eruption may be imminent. Here is a great place to find official USGS updates on the volcanism in Hawaii (including maps). This version includes earthquakes M ≥ 3.5 (note the seismicity offshore to the south, this is where the youngest Hawaii volcano is). Below are a series of plots from tide gages installed at several sites in the Hawaii Island Chain. These data are all posted online here and here. Yesterday morning, as I was recovering from working on stage crew for the 34th Reggae on the River (fundraiser for the non profit, the Mateel Community Center), I noticed on social media that there was an M 6.9 earthquake in Lombok, Indonesia. This is sad because of the likelihood for casualties and economic damage in this region. Well, yesterday while I was installing the final window in a reconstruction project, there was an earthquake along the Aleutian Island Arc (a subduction zone) in the region of the Andreanof Islands. Here is the USGS website for the M 6.6 earthquake. This earthquake is close to the depth of the megathrust fault, but maybe not close enough. So, this may be on the subduction zone, but may also be on an upper plate fault (I interpret this due to the compressive earthquake fault mechanism). The earthquake has a hypocentral depth of 20 km and the slab model (see Hayes et al., 2013 below and in the poster) is at 40 km at this location. There is uncertainty in both the slab model and the hypocentral depth. We just had a Great Earthquake in the region of the Fiji Islands, in the central-western Pacific. Great Earthquakes are earthquakes with magnitudes M ≥ 8.0. This ongoing sequence began in late July with a Mw 6.4 earthquake. Followed less than 2 weeks later with a Mw 6.9 earthquake. We just had a M 7.3 earthquake in northern Venezuela. Sadly, this large earthquake has the potential to be quite damaging to people and their belongings (buildings, infrastructure). Well, this earthquake, while having a large magnitude, was quite deep. Because earthquake intensity decreases with distance from the earthquake source, the shaking intensity from this earthquake was so low that nobody submitted a single report to the USGS “Did You Feel It?” website for this earthquake. Following the largest typhoon to strike Japan in a very long time, there was an earthquake on the island of Hokkaido, Japan today. There is lots on social media, including some spectacular views of disastrous and deadly landslides triggered by this earthquake (earthquakes are the number 1 source for triggering of landslides). These landslides may have been precipitated (sorry for the pun) by the saturation of hillslopes from the typhoon. Based upon the USGS PAGER estimate, this earthquake has the potential to cause significant economic damages, but hopefully a small number of casualties. As far as I know, this does not incorporate potential losses from earthquake triggered landslides [yet]. Today, there was a large earthquake associated with the subduction zone that forms the Kermadec Trench. Well, around 3 AM my time (northeastern Pacific, northern CA) there was a sequence of earthquakes including a mainshock with a magnitude M = 7.5. This earthquake happened in a highly populated region of Indonesia. Here is a map that shows the updated USGS model of ground shaking. The USGS prepared an updated earthquake fault slip model that was additionally informed by post-earthquake analysis of ground deformation. The original fault model extended from north of the epicenter to the northernmost extent of Palu City. Soon after the earthquake, Dr. Sotiris Valkaniotis prepared a map that showed large horizontal offsets across the ruptured fault along the entire length of the western margin on Palu Valley. This horizontal offset had an estimated ~8 meters of relative displacement. InSAR analyses confirmed that the coseismic ground deformation extended through Palu Valley and into the mountains to the south of the valley. Synthetic Aperture Radar (SAR) is a remote sensing method that uses Radar to make observations of Earth. These observations include the position of the ground surface, along with other information about the material properties of the Earth’s surface. Landslides during and following the M=7.5 earthquake in central Sulawesi, Indonesia possibly caused the majority of casualties from this catastrophic natural disaster. Volunteers (citizen scientists) have used satellite aerial imagery collected after the earthquake to document the spatial extent and magnitude of damage caused by the earthquake, landslides, and tsunami.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
In this region of the world, the Solomon Sea plate and the South Bismarck plate converge to form a subduction zone, where the Solomon Sea plate is the oceanic crust diving beneath the S.Bismarck plate. This region of the Pacific-North America plate boundary is at the northern end of the Cascadia subduction zone (CSZ). To the east, the Explorer and Juan de Fuca plates subduct beneath the North America plate to form the megathrust subduction zone fault capable of producing earthquakes in the magnitude M = 9 range. The last CSZ earthquake was in January of 1700, just almost 319 years ago. Before I looked more closely, I thought this sequence might be related to the Kefallonia fault. I prepared some earthquake reports for earthquakes here in the past, in 2015 and in 2016. There was a M = 6.8 earthquake along a transform fault connecting segments of the Mid Atlantic Ridge recently. Today’s earthquake occurred along the convergent plate boundary in southern Alaska. This subduction zone fault is famous for the 1964 March 27 M = 9.2 megathrust earthquake. I describe this earthquake in more detail here. There was a sequence of earthquakes along the subduction zone near New Caledonia and the Loyalty Islands. A large earthquake in the region of the Bering Kresla fracture zone, a strike-slip fault system that coincides with the westernmost portion of the Aleutian trench (which is a subduction zone further to the east). This magnitude M = 7.0 earthquake is related to the subduction zone that forms the Philippine trench (where the Philippine Sea plate subducts beneath the Sunda plate). Here is the USGS website for this earthquake.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
We just had a large earthquake in the region of the Bering Kresla fracture zone, a strike-slip fault system that coincides with the westernmost portion of the Aleutian trench (which is a subduction zone further to the east). I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0 in one version.
Tectonic setting of the Sredinny and Ganal Massifs in Kamchatka. Kamchatka/Aleutian junction is modified after Gaedicke et al. (2000). Onland geology is after Bogdanov and Khain (2000). 1, Active volcanoes (a) and Holocene monogenic vents (b). 2, Trench (a) and pull-apart basin in the Aleutian transform zone (b). 3, Thrust (a) and normal (b) faults. 4, Strike-slip faults. 5–6, Sredinny Massif. 5, Amphibolite-grade felsic paragneisses of the Kolpakovskaya series. 6, Allochthonous metasedimentary and metavolcanic rocks of the Malkinskaya series. 7, The Kvakhona arc. 8, Amphibolites and gabbro (solid circle) of the Ganal Massif. Lower inset shows the global position of Kamchatka. Upper inset shows main Cretaceous-Eocene tectonic units (Bogdanov and Khain 2000): Western Kamchatka (WK) composite unit including the Sredinny Massif, the Kvakhona arc, and the thick pile of Upper Cretaceous marine clastic rocks; Eastern Kamchatka (EK) arc, and Eastern Peninsulas terranes (EPT). Eastern Kamchatka is also known as the Olyutorka-Kamchatka arc (Nokleberg et al. 1998) or the Achaivayam-Valaginskaya arc (Konstantinovskaya 2000), while Eastern Peninsulas terranes are also called Kronotskaya arc (Levashova et al. 2000).
Kamchatka subduction zone. A: Major geologic structures at the Kamchatka–Aleutian Arc junction. Thin dashed lines show isodepths to subducting Pacific plate (Gorbatov et al., 1997). Inset illustrates major volcanic zones in Kamchatka: EVB—Eastern Volcanic Belt; CKD—Central
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Mw=7.3, KOMANDORSKIYE OSTROVA REGION (Depth: 18 km), 2018/12/20 17:01:54 UTC – Full details here: https://t.co/pUYUdEnFtb pic.twitter.com/u9Uv1X4v4u — Earthquakes (@geoscope_ipgp) December 20, 2018 very strong #earthquake offshore #Kamchatka, #Russia, minor, regional #tsunami expected. Fortunately, region not well inhabitat @Quake_Tracker @LastQuake @JuskisErdbeben @UKEQ_Bulletin pic.twitter.com/DwCE4NuAOd — CATnews (@CATnewsDE) December 20, 2018 Seismic waves from the M7.4 Russia earthquake have rolled across Canada during the past hour (not felt here). The fastest travelling waves took about 7 minutes to travel from Kamchatka to Dawson, Yukon. — John Cassidy (@earthquakeguy) December 20, 2018
There was a M = 6.8 earthquake along a transform fault connecting segments of the Mid Atlantic Ridge recently. (now an M 6.7) https://earthquake.usgs.gov/earthquakes/eventpage/us1000hpim/executive The Mid Atlantic Ridge is an extensional plate boundary called an oceanic spreading ridge. Oceanic crust is formed along these types of plate boundaries. I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 4.5 in one version.
Principal tectonic features of the NE Atlantic Ocean on a bathymetric and topographic map (ETOPO1). Compressional structures (folds and reverse faults) on the NE Atlantic Continental Margin are from Doré et al. [2008], Johnson et al. [2005], Hamann et al. [2005], Price et al. [1997] and Tuitt et al. [2010]. Present-day spreading rates along Reykjavik, Kolbeinsey and Mohns Ridges are from Mosar et al. [2002]. Continent-ocean boundaries of Europe and Greenland are from Gaina et al. [2009] and Olesen et al. [2007]. Black thick lines indicate seismic profiles of Figure 3. Abbreviations (north to south): GFZ, Greenland Fracture Zone; SFZ, Senja Fracture Zone; JMFZ, Jan Mayen Fracture Zone (west and east); JMMC, Jan Mayen Microcontinent; HHA, Helland Hansen Arch; OL, Ormen Lange Dome; FR, Fugløy Ridge; GIR, Greenland-Iceland Ridge; IFR: Iceland-Faeroe Ridge; MGR, Munkagrunnar Ridge; WTR, Wyville Thomson Ridge; YR, Ymir Ridge; NHBFC, North Hatton Bank Fold Complex; MHBFC, Mid-Hatton Bank Fold Complex; CGFZ, Charlie Gibbs Fracture Zone. Map
Map of magnetic anomalies, NE Atlantic Ocean. Background image is recent model EMAG2 of crustal magnetic anomalies [Maus et al., 2009]. Ages of magnetic anomalies are from Cande and Kent [1995]. Map projection is Universal Transverse Mercator (UTM, WGS 1984, zone 27N).
Positions relative to stationary Greenland plate of Europe, Jan Mayen Microcontinent (JMMC) and Iceland Mantle Plume at intervals of 10 Myr, according to stationary hot spot model of Lawver and Müller [1994] and moving hot spot model of Mihalffy et al. [2008]. Timing is (a) late Paleocene, 55.9 Ma; (b) late Eocene, 36.6 Ma ; (c) early Miocene, 19.6 Ma; and (d) present. (more info is in the original figure caption)
Magnetic anomaly and fracture zone identifications and interpreted isochrons.
(a) Free-air gravity (DTU10: Andersen 2010); (b) isostatic gravity anomaly (this was computed using the Airy–Heiskanen model, where the compensation is accomplished by variations in thickness of the constant density layers: the root is calculated using the ETOPO1 topography and bathymetry: Haase et al., this volume, in press);
magnetic anomaly (Nasuti & Olesen 2014; Gaina et al., this volume, in review); and (d) sediment thickness (Funck et al. 2014). Distribution of volcanic edifices as in Figure 1. Dark grey lines indicate the active and extinct plate boundaries
Location map of the North Atlantic and Arctic. ETOPO-2 shaded relief bathymetry and topography are based on data from Sandwell & Smith (1997). (more detail is found in the original figure caption)
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Mw=6.8, JAN MAYEN ISLAND REGION (Depth: 21 km), 2018/11/09 01:49:40 UTC – Full details here: https://t.co/gUvvmkw24e pic.twitter.com/DdtvaBq2Fc — Earthquakes (@geoscope_ipgp) November 9, 2018 Using a low pass filter highlights the Surface waves sweeping across the UK. You can clearly see that the lowest frequency components (widest spacing between wiggles) arrive before higher frequency (closer spaced wiggles) components. Scientists call this effect dispersion. pic.twitter.com/eRcZ37TtsQ — BGS schoolseismology (@Schoolseismo) November 9, 2018 Return to the Earthquake Reports page. Last night I had completed preparing for class the next day. I was about to head to bed. I got an email from the Pacific Tsunami Warning Center notifying me that there was no risk of a tsunami due to an earthquake with a magnitude M 6.6. I noticed it was along the Sovanco fault, a transform fault (right-lateral strike-slip). Strike slip faults can produce tsunami, but they are smaller than tsunami generated along subduction zones. The recent M = 7.5 Donggala Earthquake in Sulawesi, Indonesia is an example of a tsunami generated in response to a strike-slip earthquake (tho coseismic landslides may be part of the story there too). I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.5 in one version.
Map of Explorer region and surroundings. Plate boundaries are based on Riddihough’s [1984] and Davis and Riddihough’s [1982] tectonic models. Solid lines are active plate boundaries (single lines are transform faults, double lines are spreading centers, barbed lines are subduction zones with barbs in downgoing plate direction). The wide double line outlines the width of the Sovanco fracture zone, and the dots sketch the Explorer-Winona boundary. Plate motion vectors (solid arrows) are from NUVEL-1A [DeMets et al., 1994] for Pacific-North America motion and from Wilson [1993] for Pacific-Juan de Fuca and Juan de Fuca-North America motion. Open arrows are Explorer relative plate motions averaged over last 1 Myr [Riddihough, 1984] (in text, we refer to these most recent magnetically determined plate motions as the ‘‘Riddihough model’’). Winona block motions (thin arrows), described only qualitatively by Davis and Riddihough [1982], are not to scale. Abbreviations are RDW for Revere-Dellwood- Wilson, Win for Winona, FZ for fault zone, I for island, S for seamount, Pen for peninsula.
Close-up of the Pacific-Explorer boundary. Plotted are fault plane solutions (gray scheme as in Figure 3) and well-relocated earthquake epicenters. The SeaBeam data are from the RIDGE Multibeam Synthesis Project (http://imager.ldeo.columbia.edu) at the Lamont-Doherty Earth observatory. Epicenters labeled by solid triangles are pre-1964, historical earthquakes (see Appendix B). Solid lines mark plate boundaries inferred from bathymetry and side-scan data [Davis and Currie, 1993]; dashed were inactive. QCF is Queen Charlotte fault, TW are Tuzo Wilson seamounts, RDW is Revere-Dellwood-Wilson fault, DK are Dellwood Knolls, PRR is Paul Revere ridge, ER is Explorer Rift, ED is Explorer Deep, SERg is Southern Explorer ridge, ESM is Explorer seamount, SETB is Southwest Explorer Transform Boundary, SAT is Southwestern Assimilated Territory, ESDZ is Eastern Sovanco Deformation Zone, HSC is Heck seamount chain, WV is active west valley of Juan de Fuca ridge, MV is inactive middle valley.
Schematic plate tectonic reconstruction of Explorer region during the last 3 Myr. Note the transfer of crustal blocks (hatched) from the Explorer to the Pacific plate; horizontal hatch indicates transfer before 1.5 Ma and vertical hatch transfer since then. Active boundaries are shown in bold and inactive boundaries are thin dashes. Single lines are transform faults, double lines are spreading centers; barbed lines are subduction zones with barbs in downgoing plate direction. QCF is Queen Charlotte fault, TW are the Tuzo Wilson seamounts, RDW is Revere-Dellwood-Wilson fault, DK are the Dellwood Knolls, ED is Explorer Deep, ER is Explorer Rift, ERg is Explorer Ridge, ESM is Explorer Seamount, SOV is Sovanco fracture zone, ESDZ is Eastern Sovanco Deformation Zone, JRg is Juan de Fuca ridge, and NF is Nootka fault. The question mark indicates ambiguity whether spreading offshore Brooks peninsula ceased when the Dellwood Knolls became active (requiring only one independently moving plate) or if both spreading centers, for a short time span, where active simultaneously (requiring Winona block motion independent from Explorer plate during that time).
Bathymetric map of northern Juan de Fuca and Explorer Ridges. Map is composite of multibeam bathymetry and satellite altimetry (Sandwell and Smith, 1997). Principal structures are labeled: ERB—Explorer Ridge Basin, SSL—strike-slip lineation. Inset map shows conventional tectonic interpretation of region. Dashed box shows location of main figure. Solid lines are active plate boundaries, dashed line shows Winona-Explorer boundary, gray ovals represent seamount chains. Solid arrows show plate motion vectors from NUVEL-1A (DeMets et al., 1994) for Pacific–North America and from Wilson (1993) for Pacific–Juan de Fuca and Juan de Fuca–North America. Open arrows are Explorer relative motion averaged over past 1 m.y. (Riddihough, 1984). Abbreviations: RDW—Revere-Dellwood-Wilson,Win—Winona block, C.O.—Cobb offset, F.Z.—fracture zone. Endeavour segment is northernmost section of Juan de Fuca Ridge.
Structural interpretation map of Explorer–Juan de Fuca plate region based on composite multibeam bathymetry and satellite altimetry data (Fig. 1). Heavy lines are structural (fault) lineations, gray circles and ovals indicate volcanic cones and seamounts, dashed lines are turbidite channels. Location of magnetic anomaly 2A is shown; boundaries are angled to show regional strike of anomaly pattern.
Earthquake locations estimated using U.S. Navy hydrophone arrays that occurred between August 1991 and January 2002. Focal mechanisms are of large (Mw>4.5) earthquakes that occurred during same time period, taken from Pacific Geoscience Center, National Earthquake Information Center, and Harvard moment-tensor catalogs. Red mechanism shows location of 1992 Heck Seamount main shock.
Tectonic model of Explorer plate boundaries. Evidence presented here is consistent with zone of shear extending through Explorer plate well south of Sovanco Fracture Zone (SFZ) to include Heck, Heckle, and Springfield seamounts, and possibly Cobb offset (gray polygon roughly outlines shear zone). Moreover, Pacific– Juan de Fuca–North American triple junction may be reorganizing southward to establish at Cobb offset. QCF—Queen Charlotte fault.
Identification of major tectonic features in western Canada. BP—Brooks Peninsula, BPfz—Brooks Peninsula fault zone, NI— Nootka Island, QCTJ—Queen Charlotte triple junction. Dotted lines delineate extinct boundaries or shear zones. Seismic stations are displayed as inverted black triangles. Station projections along line 1 and line 2 are plotted as thick white lines. White triangles represent Alert Bay volcanic field centers. Center of array locates town of Woss. Plates: N-A—North America; EXP—Explorer; JdF—Juan de Fuca; PAC—Pacific.
The Queen Charlotte fault (QCF) zone, the islands of Haida Gwaii and adjacent area, and the locations of the 2012 Mw 7.8 (ellipse), 2013 Mw 7.5 (solid line), and 1949 Ms 8.1 (dashed) earthquakes. The along margin extent of the 1949 event is not well constrained.
Aftershocks of the 2012 Mw 7.8 Haida Gwaii thrust 13 earthquake (after Cassidy et al., 2013). They approximately define the rupture area. The normal-faulting mechanisms for two of the larger aftershocks are also shown. Many of the aftershocks are within the incoming oceanic plate and within the overriding continental plate rather than on the thrust rupture plane.
Model for the 2012 Mw 7.8 earthquake rupture and the partitioning of oblique convergence into margin parallel motion on the Queen Charlotte transcurrent fault and nearly orthogonal thrust convergence on the Haida Gwaii thrust fault.
(A) Major tectonic features describing the micro-plate model for the Explorer region. The Explorer plate (EXP) is an independent plate and is in convergent motion towards the North American plate (NAM). V.I. D Vancouver Island; PAC D the Pacific plate; JdF D the Juan the Fuca plate. The accentuated zone between the Explorer and JdF ridges is the Sovanco transform zone and the two boundary lines do not indicate the presence of faults but define the boundaries of this zone of complex deformation. (B) The key features of the pseudo-plate model for the region are a major plate boundary transform fault zone between the North American and Pacific plates and the Nootka Transform, a left-lateral transform fault north of the Juan the Fuca plate.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Ground motion visualization for the largest of the 3 #earthquakes (M6.8) off the coast of Vancouver Island https://t.co/B3F8sA1Z1D pic.twitter.com/G4YB7LRgSk — IRIS Earthquake Sci (@IRIS_EPO) October 22, 2018 Small #earthquake near Yosemite NP California riding on the surface waves of the M6.5+ #earthquakes W of Vancouver earthquakes. — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) October 22, 2018
Return to the Earthquake Reports page. I was finally getting around to writing a report for the deep Bolivia earthquake (Bolivia report here), when a M 5.3 earthquake struck offshore of the channel islands (south of Santa Cruz Island, west of Los Angeles). As is typical when an earthquake hits a populated region in the USA, the USGS websites stopped working (for the earthquakes in South America I was researching). After about half an hour or so, the websites started working again (the M 5.3 earthquake website never had a problem). I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 4.5.
EVOLUTION OF THE SAN ANDREAS FAULT.
Earthquake shaking hazards are calculated by projecting earthquake rates based on earthquake history and fault slip rates, the same data used for calculating earthquake probabilities. New fault parameters have been developed for these calculations and are included in the report of the Working Group on California Earthquake Probabilities. Calculations of earthquake shaking hazard for California are part of a cooperative project between USGS and CGS, and are part of the National Seismic Hazard Maps. CGS Map Sheet 48 (revised 2008) shows potential seismic shaking based on National Seismic Hazard Map calculations plus amplification of seismic shaking due to the near surface soils.
Map of the California Continental Borderland showing major tectonic features and moderate earthquake locations (M >5.5). The dashed box shows area of this study. The large arrows show relative plate motions for the Pacific-North America transform fault boundary (~N40° ± 2°W; RM2 and PA-1 [Plattner et al., 2007]). BP = Banning Pass, CH = Chino Hills, CP = Cajon Pass, LA = Los Angeles, PS = Palm Springs, V = Ventura, ESC = Santa Cruz Basin, ESCBZ = East Santa Cruz Basin fault zone, SCI = Santa Catalina Island, SCL = San Clemente Island, SMB = Santa Monica Basin, and SNI = San Nicolas Island. Base map from GeoMapApp/Global Multi-Resolution Topography (GMRT) [Ryan et al., 2009].
Chronology of major Cenozoic events in the Southern California region (after Wright [1991] and Legg and Kamerling [2012]). Intensity of tectonic deformation is represented by the curve. Local (Los Angeles Basin) biostratigraphic zonation is shown. The slanted labels for Neogene stages represent the time-transgressive nature of these boundaries.
Map showing bathymetry, Quaternary faults, and recent seismicity in the Outer Borderland. Fault locations are based on the high-resolution bathymetry, available high-resolution seismic reflection profiles, and published fault maps [cf. California Geological Survey (CGS), 2010]. The red symbols show magnitude-scaled (M>4) epicenters for seismicity recorded for the period of 1932 to 2013. Seismicity data and focal mechanisms are derived from the Southern California Seismograph Network catalogs, National Earthquake Information Center [2012–2013], and Legg [1980]. Focal mechanism event numbers correspond to Table S2 in the supporting information. The black rectangle shows location of Figure 10. The light blue lines show tracklines of multichannel seismic profiles—the labeled white profiles are shown in Figures 12 (124) and 13 (108 and 126).
Map showing major active tectonic elements of the northern part of the California Continental Borderland. Major active (Quaternary) faults are shown in red (SAF = San Andreas fault, ABF = Agua Blanca fault, SCF = San Clemente fault, and SCCR = Santa Cruz-Catalina Ridge, Ferrelo). Major strike-slip offsets are shown by shaded areas with estimated displacement (EK = Emery Knoll crater; Tanner Basin near DB = Dall Bank; and SDT = San Diego Trough, small pull-apart near Catalina). Other symbols show oblique fault character including transpressional restraining bends (CAT = Santa Catalina Island, CB = Cortes Bank, and TB = Tanner Bank), uplifts (SRI = Santa Rosa Island, SCz = Santa Cruz Island, SNI = San Nicolas Island, CB = Cortes Bank, TB = Tanner Bank, and SBM = San Bernardino Mountains), and transtensional pull-apart basins (SD = San Diego, ENS = Ensenada, SCB = San Clemente Basin, and SIB = San Isidro Basin). The large arrows show Pacific-North America relative plate motions with the blue dashed line (PAC-NAM) along a small circle for the RM2 [Minster and Jordan, 1978] plate motions model through San Clemente Island (SCL). Boundary between the Inner and Outer Borderland follows the East Santa Cruz Basin fault zone (dotted line; modified from Schindler [2010] and De Hoogh [2012]). Holocene volcanoes exist along the coast (SQ= San Quintín) and within the Gulf of California Rift (CP = Cerro Prieto and Obsidian Buttes, Salton Trough). Dates show year of earthquakes with mapped focal mechanisms (see Table S2 in the supporting information). SB = Santa Barbara, LA = Los Angeles, and PS = Palm Springs.
Probability density functions (PDFs) for the 19 turbidites (olive layers) in core MV0811-14JC and core SPR090106KC in Santa Barbara Basin generated from Bacon 2.2. Brackets show 95% confidence intervals. Estimate emergence times of the Newport-Inglewood Fault (Leeper et al., 2017) in pink, Ventura- Pitas Point Fault (Rockwell et al., 2016) in green, Ventura blind thrust fault (McAuliffe et al., 2015) in purple, Compton Thrust Fault (Leon et al., 2009) in yellow and the Goleta Slide Complex (Fisher et al., 2005)in gray. Age of slumped material in 14JC is indicated by wavy texture. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Cross-sectional profile A-B-C on Santa Rosa Island (see Fig. 3) showing corrected terrace elevations. SRIF shows the locations of the Santa Rosa Island fault. Error bars are the sum of the ±1 s uncertainties in wave-cut platform slope and the GPS measurement errors. Note the change in vertical exaggeration between the lower and upper plots. The green curve was qualitatively fit to the T2 data in order to create the smoothest possible curve that conforms to all points; other curves are scaled versions of the T2 curve. Point spacing is too coarse and error bars too large on the other levels to show deformation details, but the scaled curves show that every measured point is consistent with the pattern measured on T2.
General characteristics of a pull-apart basin in a dextral side-stepping fault system. The pull-apart basin is defined to develop in pure strike-slip when alpha = 0 degrees and in transtension when 0 degrees < alpha 45 degrees.
Plan view evolution of transtensional pull-apart basin model illustrated with: (a) time-lapse overhead photography; and (b) fault interpretation and incremental basin subsidence calculated from differential laser scans. Initial and final baseplate geometry shown with dashed lines; (c) basin topography at end of experiment.
Strike Slip: Did You Feel the M5.3 EQ that just took place off the Channel Islands, CA? Please let us know here: https://t.co/cHMIb35SOk pic.twitter.com/qhgXpT166c — USGS (@USGS) April 5, 2018 An #earthquake just occurred on our Santa Cruz Island bald eagle camera! Watch dad & his eaglets withstand the natural disaster. pic.twitter.com/b9AQqiZEqP — explore.org (@exploreorg) April 5, 2018 Figure 14 is a nice summary of active tectonic elements in this region: faults and recent earthquakes. Today's magnitude 5.3 seems to be similar to the 2005 magnitude 3.9 strike slip event on the Santa Rosa-Cortes Ridge (close region & focal mechanism) pic.twitter.com/Guk75RFwN3 — Lucile Bruhat (@seismolucy) April 5, 2018 Map of the felt reports received so far after M5.3 earthquake pic.twitter.com/VFUhTObCd6 — EMSC (@LastQuake) April 5, 2018 CGS @CalConservation monitoring CA coastal tide gauge recordings. — Cynthia Pridmore (@earthquakemom) April 5, 2018 Overall 11000 responses to the Did You Feel It? system for today's offshore M5.3 earthquake. Remember, "not felt" reports are welcome, too: they keep the map from being too biased by a handful of remote felt reports. pic.twitter.com/2rKdoh7BxV — Susan Hough (@SeismoSue) April 5, 2018 Webcam view of the 5.3 earlier today in SoCal, from quite near the epicenter, on Santa Cruz Island https://t.co/Wm5D7ZDx6w — Austin Elliott (@TTremblingEarth) April 5, 2018 Earthquake eagles https://t.co/TS4tX26lBq — Susan Hough (@SeismoSue) April 6, 2018 Offshore M5.3 apparently represented a successful test of the California earthquake early warning system: https://t.co/NOXdFnn4Q7 (also impressive given the poor station coverage near the epicenter) — Jascha Polet (@CPPGeophysics) April 6, 2018 #Earthquake hits Santa Barbara County, CA | M5.3 https://t.co/9aXSbk6zIA pic.twitter.com/0S6T9jIfYQ — Sismo EQ (@sismoecuador) April 6, 2018 M5.3 occurred on an unlabeled strike-slip fault in the southern California Borderland, some good visuals on the tectonics of this area can be found here:https://t.co/utfNoIywy6 pic.twitter.com/K67vLTMS8J — Jascha Polet (@CPPGeophysics) April 6, 2018 Great animation by Dr Tanya Atwater showing the evolution of southern California, including the Channel Islands which are near today's M5.3 #earthquake. pic.twitter.com/W3dJbDZtM6 — IRIS Earthquake Sci (@IRIS_EPO) April 5, 2018 View of cliffs along Santa Cruz Island during today’s earthquake. Dust rolls off cliffs as the temblor hit close to the Island, photo taken by a private fishing boat on scene during the quake. @VCFD pic.twitter.com/1lhCo9Cwqp — VCFD PIO (@VCFD_PIO) April 5, 2018 5.4 mag earthquake off Santa Cruz Island. Felt the shaking here in LA City Hall. Checking earthquake early warning for details. @kwhudnut @USGS pic.twitter.com/s0DW2ktOIH — Jeff Gorell (@JeffGorell) April 5, 2018 Earthquake Early Warning System Worked, Gave Heads-Up Before 5.3 Temblor Hit Off SoCal Coast: Officials https://t.co/Ngzsr8DqeE via @ktla — Cynthia Pridmore (@earthquakemom) April 6, 2018 . @LastQuake Woahh Californians are launching LastQuake app IMMEDIATELY after the shaking! They're real time sensors #Earthquake #California pic.twitter.com/UVfkrr9VL8 — Real News Line (@RealNewsLine) April 5, 2018 We had an M 6.8 earthquake near a transform micro-plate boundary fault system north of New Ireland, Papua New Guinea today. Here is the USGS website for this earthquake. https://earthquake.usgs.gov/earthquakes/eventpage/usp000a3sp#executive I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.5 (in a second poster). I also prepared these two posters with emag2 magnetic anomaly data (the file sizes are larger for these emag2 posters).
Tectonic setting and mineral deposits of eastern Papua New Guinea and Solomon Islands. The modern arc setting related to formation of the mineral deposits comprises, from west to east, the West Bismarck arc, the New Britain arc, the Tabar-Lihir-Tanga-Feni Chain and the Solomon arc, associated with north-dipping subduction/underthrusting at the Ramu-Markham fault zone, New Britain trench and San Cristobal trench respectively. Arrows denote plate motion direction of the Australian and Pacific plates. Filled triangles denote active subduction. Outlined triangles denote slow or extinct subduction. NBP: North Bismarck plate; SBP: South Bismarck plate; AT: Adelbert Terrane; FT: Finisterre Terrane; RMF: Ramu-Markham fault zone; NBT: New Britain trench.
3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.
Forward tectonic reconstruction of progressive arc collision and accretion of New Britain to the Papua New Guinea margin. (a) Schematic forward reconstruction of New Britain relative to Papua New Guinea assuming continued northward motion of the Australian plate and clockwise rotation of the South Bismarck plate. (b) Cross-sections illustrate a conceptual interpretation of collision between New Britain and Papua New Guinea.
Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.
Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.
Strike Slip: A very noisy, poorly constrained first-motion mechanism is strike slip: https://t.co/FXqwartB6M pic.twitter.com/owkfcJol2X — Anthony Lomax 🌍 (@ALomaxNet) March 8, 2018 Mw=6.7, NEW IRELAND REGION, P.N.G. (Depth: 32 km), 2018/03/08 17:39:50 UTC – Full details here: https://t.co/J42HsAUIAH pic.twitter.com/VlAO5b9eWJ — Earthquakes (@geoscope_ipgp) March 8, 2018 M6.8 #earthquake ENE of Taron, Papua New Guinea 17.39 UTC 8 Mar 2018 (PP wave arrival) recorded in Nottingham on 'slinky' school seismometer https://t.co/EcO1N8YwxR pic.twitter.com/oc0Fy2MqVx — Geological Outreach (@GeoOutreach) March 8, 2018 I was asleep in bed, trying to catch up to prevent myself from getting ill, when there was a large earthquake in the Gulf of Alaska (GA), offshore of Kodiak, Alaska. When I wakened, I noticed a fb message from my friend Scott Willits notifying me of an M 8.2 earthquake in Alaska, posted at 2:20 AM local time. I immediately got up to check on this and was surprised that there was not a tsunami evacuation going on. I live in the small town of Manila (population ~700), on the North Spit (a sand spit west of Arcata and Eureka, CA). I live above 10 m in elevation and do not consider myself exposed to tsunami risks, local or distant (especially given that (1) the CSZ locked zone is mostly under land here and (2) that the part of the locked zone that is not under land is in shallow water; so our local tsunami will probably be much smaller than further north, like Crescent City or Brookings). I have been involved in tsunami education and outreach for over 15 years and prepared the first tsunami hazard map for northern CA (working with Dr. Lori Dengler and the Redwood Coast Tsunami Work Group). Needless to say, I am cogent and aware about the tsunami risk here in norcal. https://earthquake.usgs.gov/earthquakes/eventpage/us2000cmy3/executive SO. I soon discovered that the GA earthquake happened in the Pacific plate, far from the subduction zone and that the earthquake was a strike-slip earthquake. Both of these facts explained why the sheriff had not been at my door earlier this morning. In addition, the magnitude had been adjusted to M 7.9 (no longer a Great earthquake, just a Large earthquake; earthquake classes are defined here). However, there were some small tsunami waves observed (see below) as reported by the National Tsunami Warning Center (see social media below). I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.5. More about the plate boundary can be found in that report.
[Top Story] Magnitude 7.9 Earthquake Gulf of Alaska. https://t.co/SbsoXcGHU9 pic.twitter.com/VkTNhiwx7l — USGS (@USGS) January 23, 2018 M=7.9 Alaska earthquake strikes off the coast of Kodiak Island, triggering a tsunami and questions | https://t.co/6d516uWWTP https://t.co/n3JIhSFClU — Ross S Stein (@rstein357) January 23, 2018 Glad this earthquake was on a strike-slip fault, about 90 km from the subduction trench where the tsunamigenic megathrust earthquakes occur. Oceanic strike-slip faults are shallow (~50km) so this must have ruptured along a very long fault of ~200 km or multiple faults segments. pic.twitter.com/q8iOKGxGW9 — Kasey Aderhold (@kaseyaderhold) January 23, 2018 .Map of sea-floor geophysical features in Gulf of Alaska from a paper in 1973 shows a number of east-west trending fracture zones in Pacific plate. Possible that today's M7.9 earthquake occurred along one of these – reasonably consistent with faulting mechanism from seismic data pic.twitter.com/jV8t0bhUkw — Stephen Hicks (@seismo_steve) January 23, 2018 Excellent story from @nytimes of last night’s earthquake offshore Alaska and small, resultant tsunami. https://t.co/DoQcPGr1XZ — The TsunamiZone (@thetsunamizone) January 23, 2018 This mornings Alaska M7.9 earthquake felt in Costa Rica with my @raspishake. pic.twitter.com/z0qUOMgIJV — Benjamin Martin (@ben7230) January 23, 2018 It took nearly 7 hours for our Middle School M7.9 #Alaska seismogram to scroll enough to show full amplitude of these large #Earthquake traces! Another #STEM #TeachableMoment thanks to funding from @IRIS_EPO & @IRIS_quakes It's why #WhyEarthScienceIsTheBestSubject pic.twitter.com/67AnOT6mmr — Dave Curry (@CarlSaganRox) January 23, 2018 Mw=8.0, GULF OF ALASKA (Depth: 17 km), 2018/01/23 09:31:40 UTC – Full details here: https://t.co/lJnOdzjhs5 pic.twitter.com/S9p9wHXrZo — Earthquakes (@geoscope_ipgp) January 23, 2018 Tue Jan 23 11:18:49 UTC 2018 event picture pic.twitter.com/ZpFFEWbkvf — NWS Tsunami Alerts (@NWS_NTWC) January 23, 2018 Possible strike-slip FirstMoMech: Mw7.6 #earthquake Gulf of Alaska https://t.co/kCIw9Vypa6 @ALomaxNet pic.twitter.com/dllZXOwBj8 — Anthony Lomax 🌍 (@ALomaxNet) January 23, 2018 GFZ Mww gives M7.8 and seems to confirm strike-slip faulting https://t.co/hN2Fju5BCW pic.twitter.com/RsOpLVa5Lj — Anthony Lomax 🌍 (@ALomaxNet) January 23, 2018 M=7.9 Alaska earthquake strikes off the coast of Kodiak Island, triggering a tsunami and questions | @temblor | https://t.co/LumawcrkQL #AlaskaEarthquake pic.twitter.com/BTZ3bpw7Cl — IRIS Earthquake Sci (@IRIS_EPO) January 23, 2018 Tsunami waves from M7.9 outer-rise earthquake detected at Kodiak tide station pic.twitter.com/CmjuLqGQ6A — Rob Witter (@WitterBanter) January 23, 2018 Current location estimate of magnitude~8 offshore Alaska earthquake 10 mins ago seems to indicate that it occurred within the oceanic Pacific plate before it subducts at the trench. Possibly a normal faulting event? Significant tsunami risk. pic.twitter.com/G5BL1HwLi3 — Stephen Hicks (@seismo_steve) January 23, 2018 Powerful earthquake jolts Alaska awake with middle-of-the-night tsunami warning, which was canceled after a few intense hours. https://t.co/1EOVhSUa40 — AP West Region (@APWestRegion) January 23, 2018 Want to explore the seismicity of #Alaska? View past and current #earthquakes using our free Interactive Earthquake Browser. You can even look at earthquake locations in 3D! https://t.co/s1XIzHPEQY #AlaskaQuake pic.twitter.com/rjHiywdcKi — IRIS Earthquake Sci (@IRIS_EPO) January 23, 2018 .Yup, a preliminary movie of the #Alaska #earthquake rupture ("back projection") indicates that the rupture propagates to the east and west of its starting point (epicentre). Agrees with faulting mechanism and plate fabric (fracture zones). Via @IRIS_EPO @alexanderhutko pic.twitter.com/TmDdzwHb36 — Stephen Hicks (@seismo_steve) January 23, 2018 Alaska #tsunami just passed @Ocean_Networks bottom pressure station at Clayoquot Slope: 3-cm sea level drop; not big but there.https://t.co/b27CdUo3as pic.twitter.com/T6A8FT2SdT — Martin Scherwath (@mscherwath) January 23, 2018 #PointArena tide gauge @ Arena Cove showing a small #tsunami this morning. This small tsunami is working its way down the coast.#cawx #earthquake #alaska pic.twitter.com/bizkraSBxs — NWS Bay Area (@NWSBayArea) January 23, 2018 Updating some earlier tide-gauge screenshots by @theearthquakes and @TTremblingEarth: can see tsunami arriving on Kodiak Island as up to 20cm fluctuations superimposed on rising tide. https://t.co/k8110ewlcV pic.twitter.com/mJHaszKGE9 — Chris Rowan (@Allochthonous) January 23, 2018 Check out the surface waves from the 8.2 (!!) in Alaska going through Lincoln Nebraska right now live (9:50UTC) https://t.co/LSGCcIbF1j — Austin Elliott (@TTremblingEarth) January 23, 2018 Regarding aftershocks: The largest is ~M5 as of 2 hours into the sequence. It looks like the aftershocks extend North-South, suggesting the fault ruptured along along a North-South oriented fault. — AK Earthquake Center (@AKearthquake) January 23, 2018 What Are 4 Levels of Tsunami Messaging? Warning > Advisory > Watch > Info Statement. Find Out What they Mean. Learn What a Tsunami Is and Be Prepared Before any Potential #tsunami Strikes. @NWS_NTWC Click here https://t.co/F6Z7MhIvRv… pic.twitter.com/TaUycap87b — Cal OES (@Cal_OES) January 23, 2018 Watch the earthquake waves from the M7.9 Alaska earthquake cross the USArray (https://t.co/lfcuOauaVB)! #AlaskaEarthquake #earthquake https://t.co/SoZMmJHvCU pic.twitter.com/jrcGL5xvg9 — IRIS Earthquake Sci (@IRIS_EPO) January 23, 2018 Watch the earthquake waves from the M7.9 Alaska earthquake cross the USArray (https://t.co/lfcuOauaVB)! #AlaskaEarthquake #earthquake https://t.co/SoZMmJHvCU pic.twitter.com/jrcGL5xvg9 — IRIS Earthquake Sci (@IRIS_EPO) January 23, 2018 IRIS Special Event page for the M7.9 #AlaskaEarthquake https://t.co/7XDDdb0IBb (Figure from the @USGS) pic.twitter.com/NJKaN3EM7H — IRIS Earthquake Sci (@IRIS_EPO) January 23, 2018 Many seismic stations in Alaska operate multiple types of instruments to fully record the seismic wavefield. Here are records from the @IRIS_EPO Global Seismographic Network station on Kodiak Island, 280 km from the source. pic.twitter.com/JJAlhUKYSe — Andy Frassetto (@drrocks1982) January 23, 2018 This morning's 7.9 earthquake occurred along a strike-slip fault. The horizontal movement of the two plates in a strike-slip fault, typically limits the threat of tsunami's pic.twitter.com/o7kgwNHqxS — Greg Diamond (@gdimeweather) January 23, 2018 If you missed my posts from earlier: #Kusatsu in Japan erupts, killing one – https://t.co/guwE7VM9DL and a M7.9 earthquakes strikes off Alaska, but luckily doesn’t generate a tsunami: https://t.co/ff8dpsGHsh — Erik Klemetti (@eruptionsblog) January 23, 2018
Earthquake Report: Panamá
This magnitude M = 6.1 earthquake appears to be associated with the transform plate boundary (strike-slip fault) that is formed between the Cocos and Nazca plates. I initially interpreted the earthquake mechanism (e.g. moment tensor) shows this to be a strike-slip earthquake along the Panamá fracture zone (PFZ). However, the earthquake is not currently deep enough according to the USGS Slab 2.0 data (that shows the depth of the megathrust subduction zone, or the top of the downgoing oceanic crust/slab). This is still possible, but it is also possible that this is in the upper plate, the Caribbean plate.
If this is in the upper plate (seems more probable), then there are several reasons for the temblor. Perhaps the PFZ is causing differential stress in the overriding plate (causing strike-slip faults to form subparallel to the PFZ and sister faults). Perhaps there is oblique relative plate motion, that is causing strain and slip partitioning in upper plate crustal faults. Perhaps there is some other complicated faulting in the upper plate that exists for some other reason (e.g. pre-existing structures inherited from the tectonic history). OR, it may be due to a combination of any of these possibilities. The fact that this earthquake (and a Christmas temblor in 2003) are aligned with the PFZ suggests that these quakes may be related to the PFZ. As Mr. Spock (Star Trek) would say, “fascinating.”
I have some early reports for quakes along this fz, though the quality of my reports have improved over time. See the May 2014 and January 2015 reports.
The Panama fracture zone (PFZ) has a few sister fracture zones, subparallel dextral (right-lateral) strike-slip faults that have been studied by looking at seismicity and structures of the seafloor. There was a series of large earthquakes in the region south of the MAT in 1934 (Camacho, 1991) ewith the largest magnitude quake at M = 7.5. Earthquakes in the magnitude 6 range are quite common for this system, with temblors M ≥ 6 over once a year.
After tweeting this report, Dr. Kristen Morell (assistant professor at U.C. Santa Barbara) pointed out to me that they did lots of work on the tectonics in the region for their Ph.D. research. I have added some figures from her work below. Morell shows that there are upper plate crustal faults that are associated with the PFZ. Dr. Morell uses a variety of methods to come to this conclusion, including geomorphology (always a great tool), fault mapping (and cross sections of thrust faults and folds), relative plate motions and reconstructions, exhumation analysis, etc. These articles are fundamental to our understanding in this region and we are lucky to have them.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
center.
within 50 to 100 km of Carnegie and Malpelo Ridges. Fit could have been improved by postulating a somewhat faster spreading rate for this region, but even so, we could not achieve as good a match as for central part of profile.
Geologic Fundamentals
Compressional:
Extensional:
Chile | South America
General Overview
Earthquake Reports
Social Media
References:
for the tectonic and biological evolution of the Americas in Geology, v. 30, no. 9, p. 795-798Return to the Earthquake Reports page.
18 April 1906 San Francisco Earthquake
Below I present a poster that shows a computer simulation that provides an estimate of the intensity of the ground shaking that may happen if the San Andreas fault slipped in a similar way that it did in 1906.
The USGS prepares these ShakeMap scenario maps so that we can have an estimate of the ground shaking from hypothetical earthquakes. I present a poster below that uses data from one of these scenarios. This is a scenario that is similar to what we think happened in 1906, but it is only a model.
There is lots about the 1906 Earthquake that I did not include, but this leaves me room for improvement for the years into the future, when we see this anniversary come again.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
This series of block diagrams shows how the subduction zone along the west coast of North America transformed into the San Andreas Fault from 30 million years ago to the present. Starting at 30 million years ago, the westward- moving North American Plate began to override the spreading ridge between the Farallon Plate and the Pacific Plate. This action divided the Farallon Plate into two smaller plates, the northern Juan de Fuca Plate (JdFP) and the southern Cocos Plate (CP). By 20 million years ago, two triple junctions began to migrate north and south along the western margin of the West Coast. (Triple junctions are intersections between three tectonic plates; shown as red triangles in the diagrams.) The change in plate configuration as the North American Plate began to encounter the Pacific Plate resulted in the formation of the San Andreas Fault. The northern Mendicino Triple Junction (M) migrated through the San Francisco Bay region roughly 12 to 5 million years ago and is presently located off the coast of northern California, roughly midway between San Francisco (SF) and Seattle (S). The Mendicino Triple Junction represents the intersection of the North American, Pacific, and Juan de Fuca Plates. The southern Rivera Triple Junction (R) is presently located in the Pacific Ocean between Baja California (BC) and Manzanillo, Mexico (MZ). Evidence of the migration of the Mendicino Triple Junction northward through the San Francisco Bay region is preserved as a series of volcanic centers that grow progressively younger toward the north. Volcanic rocks in the Hollister region are roughly 12 million years old whereas the volcanic rocks in the Sonoma-Clear Lake region north of San Francisco Bay range from only few million to as little as 10,000 years old. Both of these volcanic areas and older volcanic rocks in the region are offset by the modern regional fault system. (Image modified after original illustration by Irwin, 1990 and Stoffer, 2006.)
Tectonic History of Western North America and Southern California
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
Southern CA
Earthquake Reports
Social Media
References:
Return to the Earthquake Reports page.
Earthquake Report: 2018 Summary
However, our historic record is very short, so any thoughts about whether this year (or last, or next) has smaller (or larger) magnitude earthquakes than “normal” are limited by this small data set.
Here is a table of the earthquakes M ≥ 6.5.
Here is a plot showing the cumulative release of seismic energy. This summary is imperfect in several ways, but shows how only the largest earthquakes have a significant impact on the tally of energy release from earthquakes. I only include earthquakes M ≥ 6.5. Note how the M 7.5 Sulawesi earthquake and how little energy was released relative to the two M = 7.9 earthquakes.
Below is my summary poster for this earthquake year
This is a video that shuffles through the earthquake report posters of the year
2018 Earthquake Report Pages
Other Annual Summaries
2018 Earthquake Reports
General Overview of how to interact with these summaries
Background on the Earthquake Report posters
Magnetic Anomalies
2018.01.10 M 7.6 Cayman Trough
Based upon our knowledge of the plate tectonics of this region, I can interpret the fault plane solution for this earthquake. The M 7.6 earthquake was most likely a left-lateral strike-slip earthquake associated with the Swan fault.
2018.01.14 M 7.1 Peru
In the region of this M 7.1 earthquake, two large structures in the NP are the Nazca Ridge and the Nazca fracture zone. The Nazca fracture zone is a (probably inactive) strike-slip fault system. The Nazca Ridge is an over-thickened region of the NP, thickened as the NP moved over a hotspot located near Salas y Gomez in the Pacific Ocean east of Easter Island (Ray et al., 2012).
There are many papers that discuss how the ridge affects the shape of the megathrust fault here. The main take-away is that the NR is bull dozing into South America and the dip of the subduction zone is flat here. There is a figure below that shows the deviation of the subducting slab contours at the NR.
Well, I missed looking further into a key update paper and used figures from an older paper on my interpretive poster yesterday. Thanks to Stéphane Baize for pointing this out! Turns out, after their new analyses, the M 7.1 earthquake was in a region of higher seismogenic coupling, rather than low coupling (as was presented in my first poster).
Also, Dr. Robin Lacassin noticed (as did I) the paucity of aftershocks from yesterday’s M 7.1. This was also the case for the carbon copy 2013 M 7.1 earthquake (there was 1 M 4.6 aftershock in the weeks following the M 7.1 earthquake on 2013.09.25; there were a dozen M 1-2 earthquakes in Nov. and Dec. of 2013, but I am not sure how related they are to the M 7.1 then). I present a poster below with this in mind. I also include below a comparison of the MMI modeled estimates. The 2013 seems to have possibly generated more widespread intensities, even though that was a deeper earthquake.
2018.01.23 M 7.9 Gulf of Alaska
This is strange because the USGS fault plane is oriented east-west, leading us to interpret the fault plane solution (moment tensor or focal mechanism) as a left-lateral strike-slip earthquake. So, maybe this earthquake is a little more complicated than first presumed. The USGS fault model is constrained by seismic waves, so this is probably the correct fault (east-west).
I prepared an Earthquake Report for the 1964 Good Friday Earthquake here.
So, that being said, here is the animation I put together. I used the USGS query tool to get earthquakes from 1/22 until now, M ≥ 1.5. I include a couple inset maps presented in my interpretive posters. The music is copyright free. The animations run through twice.
Here is a screenshot of the 14 MB video embedded below. I encourage you to view it in full screen mode (or download it).
2018.02.16 M 7.2 Oaxaca, Mexico
The SSN has a reported depth of 12 km, further supporting evidence that this earthquake was in the North America plate.
This region of the subduction zone dips at a very shallow angle (flat and almost horizontal).
There was also a sequence of earthquakes offshore of Guatemala in June, which could possibly be related to the M 8.1 earthquake. Here is my earthquake report for the Guatemala earthquake.
The poster also shows the seismicity associated with the M 7.6 earthquake along the Swan fault (southern boundary of the Cayman trough). Here is my earthquake report for the Guatemala earthquake.
2018.02.25 M 7.5 Papua New Guinea
This M 7.5 earthquake (USGS website) occurred along the Papua Fold and Thrust Belt (PFTB), a (mostly) south vergent sequence of imbricate thrust faults and associated fold (anticlines). The history of this PFTB appears to be related to the collision of the Australia plate with the Caroline and Pacific plates, the delamination of the downgoing oceanic crust, and then associated magmatic effects (from decompression melting where the overriding slab (crust) was exposed to the mantle following the delamination). More about this can be found in Cloos et al. (2005).
The aftershocks are still coming in! We can use these aftershocks to define where the fault may have slipped during this M 7.5 earthquake. As I mentioned yesterday in the original report, it turns out the fault dimension matches pretty well with empirical relations between fault length and magnitude from Wells and Coppersmith (1994).
The mapped faults in the region, as well as interpreted seismic lines, show an imbricate fold and thrust belt that dominates the geomorphology here (as well as some volcanoes, which are probably related to the slab gap produced by crust delamination; see Cloos et al., 2005 for more on this). I found a fault data set and include this in the aftershock update interpretive poster (from the Coordinating Committee for Geoscience Programmes in East and Southeast Asia, CCOP).
I initially thought that this M 7.5 earthquake was on a fault in the Papuan Fold and Thrust Belt (PFTB). Mark Allen pointed out on twitter that the ~35km hypocentral depth is probably too deep to be on one of these “thin skinned” faults (see Social Media below). Abers and McCaffrey (1988) used focal mechanism data to hypothesize that there are deeper crustal faults that are also capable of generating the earthquakes in this region. So, I now align myself with this hypothesis (that the M 7.5 slipped on a crustal fault, beneath the thin skin deformation associated with the PFTB. (thanks Mark! I had downloaded the Abers paper but had not digested it fully.
2018.03.08 M 6.8 New Ireland
The main transform fault (Weitin fault) is ~40 km to the west of the USGS epicenter. There was a very similar earthquake on 1982.08.12 (USGS website).
This earthquake is unrelated to the sequence occurring on the island of New Guinea.
Something that I rediscovered is that there were two M 8 earthquakes in 1971 in this region. This testifies that it is possible to have a Great earthquake (M ≥ 8) close in space and time relative to another Great earthquake. These earthquakes do not have USGS fault plane solutions, but I suspect that these are subduction zone earthquakes (based upon their depth).
This transform system is capable of producing Great earthquakes too, as evidenced by the 2000.11.16 M 8.0 earthquake (USGS website). This is another example of two Great earthquakes (or almost 2 Great earthquakes, as the M 7.8 is not quite a Great earthquake) are related. It appears that the M 8.0 earthquake may have triggered teh M 7.8 earthquake about 3 months later (however at first glance, it seemed to me like the strike-slip earthquake might not increase the static coulomb stress on the subduction zone, but I have not spent more than half a minute thinking about this).Main Interpretive Poster with emag2
Earthquakes M≥ 6.5 with emag2
2018.03.26 M 6.6 New Britain
Today’s M 6.6 earthquake happened close in proximity to a M 6.3 from 2 days ago and a M 5.6 from a couple weeks ago. The M 5.6 may be related (may have triggered these other earthquakes), but this region is so active, it might be difficult to distinguish the effects from different earthquakes. The M 5.6 is much deeper and looks like it was in the downgoing Solomon Sea plate. It is much more likely that the M 6.3 and M 6.6 are related (I interpret that the M 6.3 probably triggered the M 6.6, or that M 6.3 was a foreshock to the M 6.6, given they are close in depth). Both M 6.3 and M 6.6 are at depths close to the depth of the subducting slab (the megathrust fault depth) at this location. So, I interpret these to be subduction zone earthquakes.
2018.03.26 M 6.9 New Britain
2018.04.02 M 6.8 Bolivia
We are still unsure what causes an earthquake at such great a depth. The majority of earthquakes happen at shallower depths, caused largely by the frictional between differently moving plates or crustal blocks (where earth materials like the crust behave with brittle behavior and not elastic behavior). Some of these shallow earthquakes are also due to internal deformation within plates or crustal blocks.
As plates dive into the Earth at subduction zones, they undergo a variety of changes (temperature, pressure, stress). However, because people cannot directly observe what is happening at these depths, we must rely on inferences, laboratory analogs, and other indirect methods to estimate what is going on.
So, we don’t really know what causes earthquakes at the depth of this Bolivia M 6.8 earthquake. Below is a review of possible explanations as provided by Thorne Lay (UC Santa Cruz) in an interview in response to the 2013 M 8.3 Okhotsk Earthquake.
2018.05.04 M 6.9 Hawai’i
Hawaii is an active volcanic island formed by hotspot volcanism. The Hawaii-Emperor Seamount Chain is a series of active and inactive volcanoes formed by this process and are in a line because the Pacific plate has been moving over the hotspot for many millions of years.
Southeast of the main Kilauea vent, the Pu‘u ‘Ö‘ö crater saw an elevation of lava into the crater, leading to overtopping of the crater (on 4/30/2018). Seismicity migrated eastward along the ERZ. This morning, there was a M 5.0 earthquake in the region of the Hilina fault zone (HFZ). I was getting ready to write something up, but I had other work that I needed to complete. Then, this evening, there was a M 6.9 earthquake between the ERZ and the HFZ.
There have been earthquakes this large in this region in the past (e.g. the 1975.1.29 M 7.1 earthquake along the HFZ). This earthquake was also most likely related to magma injection (Ando, 1979). The 1975 M 7.1 earthquake generated a small tsunami (Ando, 1979). These earthquakes are generally compressional in nature (including the earthquakes from today).
Today’s earthquake also generated a tsunami as recorded on tide gages throughout Hawaii. There is probably no chance that a tsunami will travel across the Pacific to have a significant impact elsewhere.
Temblor Reports:
2018.05.05 Pele, the Hawai’i Goddess of Fire, Lightning, Wind, and Volcanoes
2018.05.06 Pele, la Diosa Hawaiana del Fuego, los Relámpagos, el Viento y los Volcanes de Hawái
2018.08.05 M 6.9 Lombok, Indonesia
However, it is interesting because the earthquake sequence from last week (with a largest earthquake with a magnitude of M 6.4) were all foreshocks to this M 6.9. Now, technically, these were not really foreshocks. The M 6.4 has an hypocentral (3-D location) depth of ~6 km and the M 6.9 has an hypocentral depth of ~31 km. These earthquakes are not on the same fault, so I would interpret that the M 6.9 was triggered by the sequence from last week due to static coulomb changes in stress on the fault that ruptured. Given the large difference in depths, the uncertainty for these depths is probably not sufficient to state that they may be on the same fault (i.e. these depths are sufficiently different that this difference is larger than the uncertainty of their locations).
I present a more comprehensive analysis of the tectonics of this region in my earthquake report for the M 6.4 earthquake here. I especially address the historic seismicity of the region there. This M 6.9 may have been on the Flores thrust system, while the earthquakes from last week were on the imbricate thrust faults overlying the Flores Thrust. See the map from Silver et al. (1986) below. I include the same maps as in my original report, but after those, I include the figures from Koulani et al. (2016) (the paper is available on researchgate).
2018.08.15 M 6.6 Aleutians
The Andreanof Islands is one of the most active parts of the Aleutian Arc. There have been many historic earthquakes here, some of which have been tsunamigenic (in fact, the email that notified me of this earthquake was from the ITIC Tsunami Bulletin Board).
Possibly the most significant earthquake was the 1957 Andreanof Islands M 8.6 Great (M ≥ 8.0) earthquake, though the 1986 M 8.0 Great earthquake is also quite significant. As was the 1996 M 7.9 and 2003 M 7.8 earthquakes. Lest we forget smaller earthquakes, like the 2007 M 7.2. So many earthquakes, so little time.
2018.08.18 M 8.2 Fiji
This earthquake is one of the largest earthquakes recorded historically in this region. I include the other Large and Great Earthquakes in the posters below for some comparisons.
Today’s earthquake has a Moment Magnitude of M = 8.2. The depth is over 550 km, so is very very deep. This region has an historic record of having deep earthquakes here. Here is the USGS website for this M 8.2 earthquake. While I was writing this, there was an M 6.8 deep earthquake to the northeast of the M 8.2. The M 6.8 is much shallower (about 420 km deep) and also a compressional earthquake, in contrast to the extensional M 8.2.
This M 8.2 earthquake occurred along the Tonga subduction zone, which is a convergent plate boundary where the Pacific plate on the east subducts to the west, beneath the Australia plate. This subduction zone forms the Tonga trench.
2018.08.19 M 6.9 Lombok, Indonesia
Today there was an M 6.3 soon followed by an M 6.9 earthquake (and a couple M 5.X quakes).
These earthquakes have been occurring along a thrust fault system along the northern portion of Lombok, Indonesia, an island in the magamatic arc related to the Sunda subduction zone. The Flores thrust fault is a backthrust to the subduction zone. The tectonics are complicated in this region of the world and there are lots of varying views on the tectonic history. However, there has been several decades of work on the Flores thrust (e.g. Silver et al., 1986). The Flores thrust is an east-west striking (oriented) north vergent (dipping to the south) thrust fault that extends from eastern Java towards the Islands of Flores and Timor. Above the main thrust fault are a series of imbricate (overlapping) thrust faults. These imbricate thrust faults are shallower in depth than the main Flores thrust.
The earthquakes that have been happening appear to be on these shallower thrust faults, but there is a possibility that they are activating the Flores thrust itself. Perhaps further research will illuminate the relations between these shallower faults and the main player, the Flores thrust.
2018.08.21 M 7.3 Venezuela
The northeastern part of Venezuela lies a large strike-slip plate boundary fault, the El Pilar fault. This fault is rather complicated as it strikes through the region. There are thrust faults and normal faults forming ocean basins and mountains along strike.
Many of the earthquakes along this fault system are strike-slip earthquakes (e.g. the 1997.07.09 M 7.0 earthquake which is just to the southwest of today’s temblor. However, today’s earthquake broke my immediate expectations for strike-slip tectonics. There is a south vergent (dipping to the north) thrust fault system that strikes (is oriented) east-west along the Península de Paria, just north of highway 9, east of Carupano, Venezuela. Audenard et al. (2000, 2006) compiled a Quaternary Fault database for Venezuela, which helps us interpret today’s earthquake. I suspect that this earthquake occurred on this thrust fault system. I bet those that work in this area even know the name of this fault. However, looking at the epicenter and the location of the thrust fault, this is probably not on this thrust fault. When I initially wrote this report, the depth was much shallower. Currently, the hypocentral (3-D location) depth is 123 km, so cannot be on that thrust fault.
The best alternative might be the subduction zone associated with the Lesser Antilles.
2018.08.24 M 7.1 Peru
While doing my lit review, I found the Okal and Bina (1994) paper where they use various methods to determine focal mechanisms for the some deep earthquakes in northern Peru. More about focal mechanisms below. These authors created focal mechanisms for the 1921 and 1922 deep earthquakes so they could lean more about the 1970 deep earthquake. Their seminal work here forms an important record of deep earthquakes globally. These three earthquakes are all extensional earthquakes, similar to the other deep earthquakes in this region. I label the 1921 and 1922 earthquakes a couplet on the poster.
There was also a pair of earthquakes that happened in November, 2015. These two earthquakes happened about 5 minutes apart. They have many similar characteristics, suggest that they slipped similar faults, if not the same fault. I label these as doublets also.
So, there may be a doublet companion to today’s M 7.1 earthquake. However, there may be not. There are examples of both (single and doublet) and it might not really matter for 99.99% of the people on Earth since the seismic hazard from these deep earthquakes is very low.
Other examples of doublets include the 2006 | 2007 Kuril Doublets (Ammon et al., 2008) and the 2011 Kermadec Doublets (Todd and Lay, 2013).
2018.09.05 M 6.6 Hokkaido, Japan
This earthquake is in an interesting location. to the east of Hokkaido, there is a subduction zone trench formed by the subduction of the Pacific plate beneath the Okhotsk plate (on the north) and the Eurasia plate (to the south). This trench is called the Kuril Trench offshore and north of Hokkaido and the Japan Trench offshore of Honshu.
One of the interesting things about this region is that there is a collision zone (a convergent plate boundary where two continental plates are colliding) that exists along the southern part of the island of Hokkaido. The Hidaka collision zone is oriented (strikes) in a northwest orientation as a result of northeast-southwest compression. Some suggest that this collision zone is no longer very active, however, there are an abundance of active crustal faults that are spatially coincident with the collision zone.
Today’s M 6.6 earthquake is a thrust or reverse earthquake that responded to northeast-southwest compression, just like the Hidaka collision zone. However, the hypocentral (3-D) depth was about 33 km. This would place this earthquake deeper than what most of the active crustal faults might reach. The depth is also much shallower than where we think that the subduction zone megathrust fault is located at this location (the fault formed between the Pacific and the Okhotsk or Eurasia plates). Based upon the USGS Slab 1.0 model (Hayes et al., 2012), the slab (roughly the top of the Pacific plate) is between 80 and 100 km. So, the depth is too shallow for this hypothesis (Kuril Trench earthquake) and the orientation seems incorrect. Subduction zone earthquakes along the trench are oriented from northwest-southweast compression, a different orientation than today’s M 6.6.
So today’s M 6.6 earthquake appears to have been on a fault deeper than the crustal faults, possibly along a deep fault associated with the collision zone. Though I am not really certain. This region is complicated (e.g. Kita et al., 2010), but there are some interpretations of the crust at this depth range (Iwasaki et al., 2004) shown in an interpreted cross section below.
Temblor Reports:
2018.09.06 Violent shaking triggers massive landslides in Sapporo Japan earthquake
2018.09.09 M 6.9 Kermadec
This earthquake was quite deep, so was not expected to generate a significant tsunami (if one at all).
There are several analogies to today’s earthquake. There was a M 7.4 earthquake in a similar location, but much deeper. These are an interesting comparison because the M 7.4 was compressional and the M 6.9 was extensional. There is some debate about what causes ultra deep earthquakes. The earthquakes that are deeper than about 40-50 km are not along subduction zone faults, but within the downgoing plate. This M 6.9 appears to be in a part of the plate that is bending (based on the Benz et al., 2011 cross section). As plates bend downwards, the upper part of the plate gets extended and the lower part of the plate experiences compression.
2018.09.28 M 7.5 Sulawesi
This area of Indonesia is dominated by a left-lateral (sinistral) strike-slip plate boundary fault system. Sulawesi is bisected by the Palu-Kola / Matano fault system. These faults appear to be an extension of the Sorong fault, the sinistral strike-slip fault that cuts across the northern part of New Guinea.
There have been a few earthquakes along the Palu-Kola fault system that help inform us about the sense of motion across this fault, but most have maximum magnitudes mid M 6.
GPS and block modeling data suggest that the fault in this area has a slip rate of about 40 mm/yr (Socquet et al., 2006). However, analysis of offset stream channels provides evidence of a lower slip rate for the Holocene (last 12,000 years), a rate of about 35 mm/yr (Bellier et al., 2001). Given the short time period for GPS observations, the GPS rate may include postseismic motion earlier earthquakes, though these numbers are very close.
Using empirical relations for historic earthquakes compiled by Wells and Coppersmith (1994), Socquet et al. (2016) suggest that the Palu-Koro fault system could produce a magnitude M 7 earthquake once per century. However, studies of prehistoric earthquakes along this fault system suggest that, over the past 2000 years, this fault produces a magnitude M 7-8 earthquake every 700 years (Bellier et al., 2006). So, it appears that this is the characteristic earthquake we might expect along this fault.
Most commonly, we associate tsunamigenic earthquakes with subduction zones and thrust faults because these are the types of earthquakes most likely to deform the seafloor, causing the entire water column to be lifted up. Strike-slip earthquakes can generate tsunami if there is sufficient submarine topography that gets offset during the earthquake. Also, if a strike-slip earthquake triggers a landslide, this could cause a tsunami. We will need to wait until people take a deeper look into this before we can make any conclusions about the tsunami and what may have caused it.
My 2018.10.01 BC Newshour Interview
InSAR Analysis
Interferometric SAR (InSAR) utilizes two separate SAR data sets to determine if the ground surface has changed over time, the time between when these 2 data sets were collected. More about InSAR can be found here and here. Explaining the details about how these data are analyzed is beyond the scope of this report. I rely heavily on the expertise of those who do this type of analysis, for example Dr. Eric Fielding.
M 7.5 Landslide Model vs. Observation Comparison
Until these landslides are analyzed and compared with regions that did not fail in slope failure, we will not be able to reconstruct what happened… why some areas failed and some did not.
There are landslide slope stability and liquefaction susceptibility models based on empirical data from past earthquakes. The USGS has recently incorporated these types of analyses into their earthquake event pages. More about these USGS models can be found on this page.
I prepared some maps that compare the USGS landslide and liquefaction probability maps. Below I present these results along with the MMI contours. I also include the faults mapped by Wilkinson and Hall (2017). Shown are the cities of Donggala and Palu. Also shown are the 2 tide gage locations (Pantoloan Port – PP and Mumuju – M). I also used post-earthquake satellite imagery to outline the largest landslides in Palu Valley, ones that appear to be lateral spreads.
Temblor Reports:
2018.09.28 The Palu-Koro fault ruptures in a M=7.5 quake in Sulawesi, Indonesia, triggering a tsunami and likely more shocks
2018.10.03 Tsunami in Sulawesi, Indonesia, triggered by earthquake, landslide, or both
2018.10.16 Coseismic Landslides in Sulawesi, Indonesia
2018.10.10 M 7.0 New Britain, PNG
The subduction zone forms the New Britain Trench with an axis that trends east-northeast. To the east of New Britain, the subduction zone bends to the southeast to form the San Cristobal and South Solomon trenches. Between these two subduction zones is a series of oceanic spreading ridges sequentially offset by transform (strike slip) faults.
Earthquakes along the megathrust at the New Britain trench are oriented with the maximum compressive stress oriented north-northwest (perpendicular to the trench). Likewise, the subduction zone megathrust earthquakes along the S. Solomon trench compress in a northeasterly direction (perpendicular to that trench).
There is also a great strike slip earthquake that shows that the transform faults are active.
This earthquake was too small and too deep to generate a tsunami.
Temblor Reports:
2018.10.10 M 7.5 Earthquake in New Britain, Papua New Guinea
2018.10.22 M 6.8 Explorer plate
The Juan de Fuca plate is created at an oceanic spreading center called the Juan de Fuca Ridge. This spreading ridge is offset by several transform (strike-slip) faults. At the southern terminus of the JDF Ridge is the Blanco fault, a transtensional transform fault connecting the JDF and Gorda ridges.
At the northern terminus of the JDF Ridge is the Sovanco transform fault that strikes to the northwest of the JDF Ridge. There are additional fracture zones parallel and south of the Sovanco fault, called the Heck, Heckle, and Springfield fracture zones.
The first earthquake (M = 6.6) appears to have slipped along the Sovanco fault as a right-lateral strike-slip earthquake. Then the M 6.8 earthquake happened and, given the uncertainty of the location for this event, occurred on a fault sub-parallel to the Sovanco fault. Then the M 6.5 earthquake hit, back on the Sovanco fault.
2018.10.25 M 6.8 Greece
Both of those earthquakes were right-lateral strike-slip earthquakes associated with the Kefallonia fault.
However, today’s earthquake sequence was further to the south and east of the strike-slip fault, in a region experiencing compression from the Ionian Trench subduction zone. But there is some overlap of these different plate boundaries, so the M 6.8 mainshock is an oblique earthquake (compressional and strike-slip). Based upon the sequence, I interpret this earthquake to be right-lateral oblique. I could be wrong.
Temblor Reports:
2018.10.26 Greek earthquake in a region of high seismic hazard
2018.11.08 M 6.8 Mid Atlantic Ridge (Jan Mayen fracture zone)
North of Iceland, the MAR is offset by many small and several large transform faults. The largest transform fault north of Iceland is called the Jan Mayen fracture zone, which is the location for the 2018.11.08 M = 6.8 earthquake.
2018.11.30 M 7.0 Alaska
During the 1964 earthquake, the downgoing Pacific plate slipped past the North America plate, including slip on “splay faults” (like the Patton fault, no relation, heheh). There was deformation along the seafloor that caused a transoceanic tsunami.
The Pacific plate has pre-existing zones of weakness related to fracture zones and spreading ridges where the plate formed and are offset. There was an earthquake in January 2016 that may have reactivated one of these fracture zones. This earthquake (M = 7.1) was very deep (~130 km), but still caused widespread damage.
The earthquake appears to have a depth of ~40 km and the USGS model for the megathrust fault (slab 2.0) shows the megathrust to be shallower than this earthquake. There are generally 2 ways that may explain the extensional earthquake: slab tension (the downgoing plate is pulling down on the slab, causing extension) or “bending moment” extension (as the plate bends downward, the top of the plate stretches out.
Temblor Reports:
2018.11.30 Exotic M=7.0 earthquake strikes beneath Anchorage, Alaska
2018.12.11 What the Anchorage earthquake means for the Bay Area, Southern California, Seattle, and Salt Lake City
2018.12.05 M 7.5 New Caledonia
This part of the plate boundary is quite active and I have a number of earthquake reports from the past few years (see below, a list of earthquake reports for this region).
But the cool thing from a plate tectonics perspective is that there was a series of different types of earthquakes. At first view, it appears that there was a mainshock with a magnitude of M = 7.5. There was a preceding M 6.0 earthquake which may have been a foreshock.
The M 7.5 earthquake was an extensional earthquake. This may be due to either extension from slab pull or due to extension from bending of the plate. More on this later.
Following the M 7.5, there was an M 6.6 earthquake, however, this was a thrust or reverse (compressional) earthquake. The M 6.6 may have been in the upper plate or along the subduction zone megathrust fault, but we won’t know until the earthquake locations are better determined.
A similar sequence happened in October/November 2017. I prepared two reports for this sequence here and here. Albeit, in 2017, the thrust earthquake was first (2017.10.31 vs. 2017.11.19).
There have been some observations of tsunami. Below is from the Pacific Tsunami Warning Center.
2018.12.20 M 7.4 Bering Kresla
This earthquake happened in an interesting region of the world where there is a junction between two plate boundaries, the Kamchatka subduction zone with the Aleutian subduction zone / Bering-Kresla Shear Zone. The Kamchatka Trench (KT) is formed by the subduction (a convergent plate boundary) beneath the Okhotsk plate (part of North America). The Aleutian Trench (AT) and Bering-Kresla Shear Zone (BKSZ) are formed by the oblique subduction of the Pacific plate beneath the Pacific plate. There is a deflection in the Kamchatka subduction zone north of the BKSZ, where the subduction trench is offset to the west. Some papers suggest the subduction zone to the north is a fossil (inactive) plate boundary fault system. There are also several strike-slip faults subparallel to the BKSZ to the north of the BKSZ.
UPDATE #1
2018.12.29 M 7.0 Philippines
The earthquake was quite deep, which makes it less likely to cause damage to people and their belongings (e.g. houses and roads) and also less likely that the earthquake will trigger a trans-oceanic tsunami.
Here are the tidal data:
Geologic Fundamentals
Compressional:
Extensional:
Return to the Earthquake Reports page.
Earthquake Report: Bering Kresla / Pacific plate
At first, when I noticed the location, I hypothesized that this may be a strike-slip earthquake. womp womp. The earthquake mechanism from the USGS shows that this M = 7.4 earthquake was a normal fault earthquake (extension).
This earthquake happened in an interesting region of the world where there is a junction between two plate boundaries, the Kamchatka subduction zone with the Aleutian subduction zone / Bering-Kresla Shear Zone. The Kamchatka Trench (KT) is formed by the subduction (a convergent plate boundary) beneath the Okhotsk plate (part of North America). The Aleutian Trench (AT) and Bering-Kresla Shear Zone (BKSZ) are formed by the oblique subduction of the Pacific plate beneath the Pacific plate. There is a deflection in the Kamchatka subduction zone north of the BKSZ, where the subduction trench is offset to the west. Some papers suggest the subduction zone to the north is a fossil (inactive) plate boundary fault system. There are also several strike-slip faults subparallel to the BKSZ to the north of the BKSZ.
Today’s M = 7.4 earthquake shows northwest-southeast directed extension. This is consistent with slab tension in the direction of the Kurile subduction zone. It may also represent extension due to bending in the Pacific plate, but this seems less likely to me. Basically, the Pacific plate, as it subducts beneath the Okhotsk plate, the downgoing slab (the plate) exerts forces on the rest of the plate that pulls it down, into the subduction zone.
A second cool thing about this earthquake is that this may be evidence that the Kuril subduction zone extends north of the intersection of the BKSZ with Kamchatka. I discussed this in my earthquake report from 2017 here.
There are a couple analogy earthquakes, but one is the best. There were several strike-slip earthquakes nearby in 1982, 1987, and 1999. However, there was a M = 6.2 earthquake in almost the same location as the M = 7.4 from today. This M = 6.2 earthquake was slightly deeper (33 km) relative to the M = 7.4 (9.6 km).Check out my update here
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Magnetic Anomalies
Age of Oceanic Lithosphere
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
Kamchatka Depression (rift-like tectonic structure, which accommodates the northern end of EVB); SR—Sredinny Range. Distribution of Quaternary volcanic rocks in EVB and SR is shown in orange and green, respectively. Small dots are active vol canoes. Large circles denote CKD volcanoes: T—Tolbachik; K l — K l y u c h e v s k o y ; Z—Zarechny; Kh—Kharchinsky; Sh—Shiveluch; Shs—Shisheisky Complex; N—Nachikinsky. Location of profiles shown in Figures 2 and 3 is indicated. B: Three dimensional visualization of the Kamchatka subduction zone from the north. Surface relief is shown as semi-transparent layer. Labeled dashed lines and color (blue to red) gradation of subducting plate denote depths to the plate from the earth surface (in km). Bold arrow shows direction of Pacific Plate movement.
Geologic Fundamentals
Compressional:
Extensional:
Alaska | Kamchatka | Kurile
General Overview
Earthquake Reports
Social Media
Quake details: https://t.co/sCHEMhsY7g
Tsunami info: https://t.co/kIFgUWkdzj pic.twitter.com/15ixlcPRld
References:
Return to the Earthquake Reports page.
Earthquake Report: Mid Atlantic Ridge
Transform faults are faults that move side-by-side (i.e. strike-slip faults) that offset spreading ridges. Learn more about different types of faults in the geologic fundamentals section below.
The Atlantic Ocean is known for the spreading center, Mid Atlantic Ridge (MAR), which was probably born in the mid Cretaceous Period, about 130 million years ago. We use the age of the oceanic crust at the eastern and western margins of the Atlantic Ocean as a basis for this interpretation.
The Mid Atlantic Ridge also splits apart the island of Iceland, which also overlies a volcanic hot spot. I have always wanted to visit Iceland to see the rocks get older as I might travel east or west from the middle of Iceland.
North of Iceland, the MAR is offset by many small and several large transform faults. The largest transform fault north of Iceland is called the Jan Mayen fracture zone, which is the location for the 2018.11.08 M = 6.8 earthquake.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes. I also include the IPGP focal mechanism as that was available before the USGS moment tensor was available (I included it in my initial poster).
Magnetic Anomalies
Age of Oceanic Lithosphere
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
projection is Universal Transverse Mercator (UTM, WGS 1984, zone 27N).
Geologic Fundamentals
Compressional:
Extensional:
Atlantic
Earthquake Reports
Social Media
References:
Earthquake Report: Explorer plate
I thought I could put together a map in short time as I already had a knowledge base for this area (e.g. earthquake reports from 2017.01.07 and 2016.03.18). However, as I was creating base maps in Google Earth, before I completed making a set (the posters below each take 4 different basemaps displayed at different transparencies), there was the M 6.8 earthquake. Then there was the M 6.6 earthquake. I had to start all over. Twice. Heheh.
This region of the Pacific-North America plate boundary is at the northern end of the Cascadia subduction zone (CSZ). To the east, the Explorer and Juan de Fuca plates subduct beneath the North America plate to form the megathrust subduction zone fault capable of producing earthquakes in the magnitude M = 9 range. The last CSZ earthquake was in January of 1700, just almost 319 years ago.
The Juan de Fuca plate is created at an oceanic spreading center called the Juan de Fuca Ridge. This spreading ridge is offset by several transform (strike-slip) faults. At the southern terminus of the JDF Ridge is the Blanco fault, a transtensional transform fault connecting the JDF and Gorda ridges.
At the northern terminus of the JDF Ridge is the Sovanco transform fault that strikes to the northwest of the JDF Ridge. There are additional fracture zones parallel and south of the Sovanco fault, called the Heck, Heckle, and Springfield fracture zones.
The first earthquake (M = 6.6) appears to have slipped along the Sovanco fault as a right-lateral strike-slip earthquake. Then the M 6.8 earthquake happened and, given the uncertainty of the location for this event, occurred on a fault sub-parallel to the Sovanco fault. Then the M 6.5 earthquake hit, back on the Sovanco fault.
So, I would consider the M 6.6 to be a mainshock that triggered the M 6.8. The M 6.5 is an aftershock of the M 6.6.
Based upon our knowledge of how individual earthquakes can change the stress (or strain) in the surrounding earth, it is unlikely that this earthquake sequence changed the stress on the megathrust. Over time, hundreds of these earthquakes do affect the potential for earthquakes on the CSZ megathrust. But, individual earthquakes (or even a combination of these 3 earthquakes) do not change the chance that there will be an earthquake on the CSZ megathrust. The chance of an earthquake tomorrow is about the same as the chance of an earthquake today. Day to day the chances don’t change much. However, year to year, the chances of an earthquake get higher and higher. But of course, we cannot predict when an earthquake will happen.
So, if we live, work, or play in earthquake country, it is best to always be prepared for an earthquake, for tsunami, and for landslides.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
I include the earthquake mechanisms for 2 special earthquakes that happened in the past two decades along this plate boundary system. In 2001 the M 6.8 Nisqually earthquake struck the Puget Sound region of Washington causing extensive damage. This earthquake was an extensional earthquake in the downgoing JDF plate. The damage was extensive because the earthquake was close to an urban center, where there was lots of infrastructure to be damaged (the closer to an earthquake, the higher the shaking intensity).
In 2012 was a M = 7.8 earthquake along the northern extension of the CSZ. The northern part of the CSZ is a very interesting region, often called the Queen Charlotte triple junction. There are some differences than the Mendocino triple junction to the south, in northern California. There continues to be some debate about how the plate boundary faults are configured here. The Queen Charlotte is a right lateral strike slip fault that extends from south of Haida Gwaii (the large island northwest of Vancouver Island) up northwards, where it is called the Fairweather fault. There are several large strike-slip earthquakes on the Queen Charlotte/Fairweather fault system in the 20th century. However, the 2012 earthquake was a subduction zone fault, evidence that the CSZ megathrust (or some semblance of this subduction zone) extends beneath Haida Gwaii (so the CSZ and QCF appear to over lap).
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Some Relevant Discussion and Figures
Dziak, 2006
Geologic Fundamentals
Compressional:
Extensional:
Cascadia subduction zone
General Overview
Earthquake Reports
Gorda plate
Blanco fracture zone
Mendocino fault
Mendocino triple junction
North America plate
Explorer plate
Uncertain
Social Media
Velocity (above) and acceleration (below, shows higher frequencies)https://t.co/pudAofzBZlhttps://t.co/bNfQHu9bf1 pic.twitter.com/z5YWbHer2R
References:
Earthquake Report: Channel Islands
The Los Angeles region is dominated by the tectonics associated with the North America – Pacific transform plate boundary system of the San Andreas fault (SAF). The SAF accommodates the majority of plate motion between these two plates. There are sister faults where some of the plate boundary motion also goes. This plate boundary extends from the Pacific Ocean eastwards to Utah (the Wasatch fault system).
The SAF is considered a “mature” strike-slip fault because it is straight along most of the system. We think that strike-slip faults start out as smaller faults that develop as tectonic strain enters a region that is different from prior strain. As time passes, these smaller faults join each other, to align with the great circle aligned to the euler pole (the axis of rotation for plates).
The SAF does bend in some places, most notably in southern CA. This bend creates complexities in the fault, but also results in north-south compression (and thrust faults) forming the Transverse Ranges north of the LA Basin. Recent work by the California Geological Survey has been focusing on these thrust faults as they strike (trend) through Hollywood. These thrust faults are oriented east-west.
There are also additional faults offshore of LA in what is called the borderlands. Many of these faults are sub-parallel to the SAF. The best example is the Newport Inglewood fault (NIF), the locus of the 1933 Long Beach Earthquake. This fault is offshore, but also extends onshore. The NIF is generally a northwest-southeast striking right lateral strike-slip fault just like the SAF.
Some of the east-west faults also extend offshore. Onshore, they are generally thrust faults, but less is known about what they do offshore (i.e. they could have some strike-slip motion too).
Today’s earthquake happened south of Santa Catalina Island, where there is a major fault system that runs through the island: the Santa Cruz Island fault. This fault is mostly a left-lateral strike-slip fault, with a small portion of reverse (compression) motion (Pinter et al, 1998, 2001).
To the north of SC Island, is the Santa Barbara Basin, an oceanic basin that preserves an excellent record of flood and earthquake triggered sedimentary deposits.
If today’s M 5.3 is possibly related to the faults that form the Santa Cruz Basin. I provide some maps of this region below the interpretive poster. Based upon the work conducted by Schindler for their MS Thesis, Today’s earthquake appears associated with the East Santa Cruz Basin fault system (supporting that this was a left-lateral strike-slip earthquake). This is not included in the USGS active fault and fold database, but today’s earthquake suggests that it could be added.
These sedimentary basins are most likely formed from extension when the orientation of strike slip faults is not parallel to the plate motion. These are called “pull apart” basins and are a result of “transtension.” Do an internet search for more about transtension and how pull apart basins can form.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 5.3 earthquake, in addition to some relevant historic earthquakes.
I include some inset figures.
USGS Earthquake Pages
These are from this current sequence
Some Relevant Discussion and Figures
This series of block diagrams shows how the subduction zone along the west coast of North America transformed into the San Andreas Fault from 30 million years ago to the present. Starting at 30 million years ago, the westward- moving North American Plate began to override the spreading ridge between the Farallon Plate and the Pacific Plate. This action divided the Farallon Plate into two smaller plates, the northern Juan de Fuca Plate (JdFP) and the southern Cocos Plate (CP). By 20 million years ago, two triple junctions began to migrate north and south along the western margin of the West Coast. (Triple junctions are intersections between three tectonic plates; shown as red triangles in the diagrams.) The change in plate configuration as the North American Plate began to encounter the Pacific Plate resulted in the formation of the San Andreas Fault. The northern Mendicino Triple Junction (M) migrated through the San Francisco Bay region roughly 12 to 5 million years ago and is presently located off the coast of northern California, roughly midway between San Francisco (SF) and Seattle (S). The Mendicino Triple Junction represents the intersection of the North American, Pacific, and Juan de Fuca Plates. The southern Rivera Triple Junction (R) is presently located in the Pacific Ocean between Baja California (BC) and Manzanillo, Mexico (MZ). Evidence of the migration of the Mendicino Triple Junction northward through the San Francisco Bay region is preserved as a series of volcanic centers that grow progressively younger toward the north. Volcanic rocks in the Hollister region are roughly 12 million years old whereas the volcanic rocks in the Sonoma-Clear Lake region north of San Francisco Bay range from only few million to as little as 10,000 years old. Both of these volcanic areas and older volcanic rocks in the region are offset by the modern regional fault system. (Image modified after original illustration by Irwin, 1990 and Stoffer, 2006.)
Geologic Fundamentals
Compressional:
Extensional:
Social Media
NO INDICATION of local tsunami generated from offshore M5.3 earthquake. pic.twitter.com/flm0ALVJag
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
Southern CA
Earthquake Reports
References:
Earthquake Report: New Ireland!
The main transform fault (Weitin fault) is ~40 km to the west of the USGS epicenter. There was a very similar earthquake on 1982.08.12 (USGS website).
This earthquake is unrelated to the sequence occurring on the island of New Guinea.
Something that I rediscovered is that there were two M 8 earthquakes in 1971 in this region. This testifies that it is possible to have a Great earthquake (M ≥ 8) close in space and time relative to another Great earthquake. These earthquakes do not have USGS fault plane solutions, but I suspect that these are subduction zone earthquakes (based upon their depth).
This transform system is capable of producing Great earthquakes too, as evidenced by the 2000.11.16 M 8.0 earthquake (USGS website). This is another example of two Great earthquakes (or almost 2 Great earthquakes, as the M 7.8 is not quite a Great earthquake) are related. It appears that the M 8.0 earthquake may have triggered teh M 7.8 earthquake about 3 months later (however at first glance, it seemed to me like the strike-slip earthquake might not increase the static coulomb stress on the subduction zone, but I have not spent more than half a minute thinking about this).Here are the USGS websites for the earthquakes discussed here.
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 6.8 earthquake, in addition to some relevant historic earthquakes.
I include some inset figures.
Main Interpretive Poster
Main Interpretive Poster with emag2
Earthquakes M≥ 6.5
Earthquakes M≥ 6.5 with emag2
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Social Media
New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec
General Overview
Earthquake Reports
References:
Earthquake Report: Gulf of Alaska!
This earthquake appears to be located along a reactivated fracture zone in the GA. There have only been a couple earthquakes in this region in the past century, one an M 6.0 to the east (though this M 6.0 was a thrust earthquake). The Gulf of Alaska shear zone is even further to the east and has a more active historic fault history (a pair of earthquakes in 1987-1988). The magnetic anomalies (formed when the Earth’s magnetic polarity flips) reflect a ~north-south oriented spreading ridge (the anomalies are oriented north-south in the region of today’s earthquake). There is a right-lateral offset of these magnetic anomalies located near the M 7.9 epicenter. Interesting that this right-lateral strike-slip fault (?) is also located at the intersection of the Gulf of Alaska shear zone and the 1988 M 7.8 earthquake (probably just a coincidence?). However, the 1988 M 7.8 earthquake fault plane solution can be interpreted for both fault planes (it is probably on the GA shear zone, but I don’t think that we can really tell).
This is strange because the USGS fault plane is oriented east-west, leading us to interpret the fault plane solution (moment tensor or focal mechanism) as a left-lateral strike-slip earthquake. So, maybe this earthquake is a little more complicated than first presumed. The USGS fault model is constrained by seismic waves, so this is probably the correct fault (east-west).
I prepared an Earthquake Report for the 1964 Good Friday Earthquake here.
UPDATES Below is a list of all the reports associated with this earthquake sequence.Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 7.9 earthquake, in addition to some relevant historic earthquakes.
I include some inset figures.
Some Relevant Discussion and Figures
Social Media
Alaska | Kamchatka | Kurile
General Overview
Earthquake Reports
References: