Well, I was on the road for 1.5 days (work party for the Community Village at the Oregon Country Fair). As I was driving home, there was a magnitude M 5.6 earthquake in coastal northern California.
https://earthquake.usgs.gov/earthquakes/eventpage/nc73201181/executive
I didn’t realize this until I was almost home (finally hit the sack around 4 am).
This earthquake follows a sequence of quakes further to the northwest, however their timing is merely a coincidence. Let me repeat this. The M 5.6 earthquake is not related to the sequence of earthquakes along the Blanco fracture zone.
Contrary to what people have posted on social media, there was but a single earthquake. This earthquake happened beneath the area of Petrolia, nearby the 1991 Honeydew Earthquake. More about the Honeydew Earthquake can be found here.
This region also had a good sized shaker in 1992, the Cape Mendocino Earthquake, which led to the development of the National Tsunami Hazard Mitigation Program. More about the Cape Mendocino Earthquake can be found on the 25th anniversary page here and in my earthquake report here.
The regional tectonics in coastal northern California are dominated by the Pacific-North America plate boundary. North of Cape Mendocino, this plate boundary is convergent and forms the Cascadia subduction zone (CSZ). To the south of Cape Mendocino, the plate boundary is the right-lateral (dextral) San Andreas fault (SAF). Where these 2 fault systems meet, there is another plate boundary system, the right-lateral strike-slip Mendocino fault (don’t write Mendocino fracture zone on your maps!). Where these 3 systems meet is called the Mendocino triple junction (MTJ).
The MTJ is a complicated region as these plate boundaries overlap in ways that we still do not fully understand. Geologic mapping in the mid- to late-20th century provides some basic understanding of the long term history. However, recent discoveries have proven that this early work needs to be revisited as there are many unanswered questions (and some of this early work has been demonstrated to be incorrect). Long live science!
Last night’s M 5.6 temblor happened where one strand of the MF trends onshore (another strand bends towards the south). But, it also is where the SAF trends onshore. At this point, I am associating this earthquake with the MF (so, a right-lateral strike-slip earthquake). The mechanism suggest that this is not a SAF related earthquake. However, it is oriented in a way that it could be in the Gorda plate (making it a left-lateral strike-slip earthquake). However, this quake is at the southern edge of the Gorda plate (sedge), so it is unlikely this is a Gorda plate event.
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 ≥ 5.0 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 ~north-south trends of these red and blue stripes in the Pacific plate. 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 North America plate, so the magnetic anomalies from the overlying Sunda plate mask the evidence for the Juan de Fuca and Gorda plates.
Magnetic Anomalies
- In a map below, I include a transparent overlay of the Global Strain Rate Map (Kreemer et al., 2014).
- The mission of the Global Strain Rate Map (GSRM) project is to determine a globally self-consistent strain rate and velocity field model, consistent with geodetic and geologic field observations. The overall mission also includes:
- contributions of global, regional, and local models by individual researchers
- archive existing data sets of geologic, geodetic, and seismic information that can contribute toward a greater understanding of strain phenomena
- archive existing methods for modeling strain rates and strain transients
- The completed global strain rate map will provide a large amount of information that is vital for our understanding of continental dynamics and for the quantification of seismic hazards.
- The version used in the poster(s) below is an update to the original 2004 map (Kreemer et al., 2000, 2003; Holt et al., 2005).
Global Strain
- n the upper left corner is a map of the Cascadia subduction zone (CSZ) and regional tectonic plate boundary faults. This is modified from several sources (Chaytor et al., 2004; Nelson et al., 2004)
Below the CSZ map is an illustration modified from Plafker (1972). This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. - In the lower right corner is a map that shows a comparison between the USGS Did You Feel It? reports and the USGS Modified Mercalli Intensity shakemap model. This comparison shows that the model is a decent fit for the reports from real people. If you felt the earthquake, please submit a report to the USGS here.
- In the upper right corner I include a larger scale view of seismicity for this area. I highlight the important historic events (e.g. the 1991 Honeydew Earthquake and the 1992 Cape Mendocino Earthquake sequence.
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.
- Here is the map with a century’s seismicity plotted.
- Here is the map with a century’s seismicity plotted along with the Global Strain Map with a 30% transparency.
- Here is the educational interpretive poster from the 1992 Cape Mendocino Earthquake (report here).
- The USGS has been increasing the list of products that are produced in association with their earthquake pages. One of these products is an earthquake forecast (not a prediction as nobody can predict earthquakes yet) that lists the chance of an earthquake with a given magnitude over a certain period of time. The forecast for the M 5.6 earthquake is found here. These forecasts are updated periodically, so the information will change with time. Below is a table where I present the forecast as it was when I checked the page this morning (would be nice if the USGS would produce an easy to read table).
- More earthquakes than usual (called aftershocks) will continue to occur near the mainshock.
- When there are more earthquakes, the chance of a large earthquake is greater which means that the chance of damage is greater.
- The USGS advises everyone to be aware of the possibility of aftershocks, especially when in or around vulnerable structures such as unreinforced masonry buildings.
- This earthquake could be part of a sequence. An earthquake sequence may have larger and potentially damaging earthquakes in the future, so remember to: Drop, Cover, and Hold on.
- According to our forecast, over the next 1 Week there is a < 1 % chance of one or more aftershocks that are larger than magnitude 5.6. It is likely that there will be smaller earthquakes over the next 1 Week, with 0 to 11 magnitude 3 or higher aftershocks. Magnitude 3 and above are large enough to be felt near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.
- No one can predict the exact time or place of any earthquake, including aftershocks. Our earthquake forecasts give us an understanding of the chances of having more earthquakes within a given time period in the affected area. We calculate this earthquake forecast using a statistical analysis based on past earthquakes.
- Our forecast changes as time passes due to decline in the frequency of aftershocks, larger aftershocks that may trigger further earthquakes, and changes in forecast modeling based on the data collected for this earthquake sequence.
From the USGS:
Be ready for more earthquakes
What we think will happen next
About our earthquake forecasts
- Gosh, almost forgot to include this photo of the seismic waves recorded on the Humboldt State University Department of Geology Baby Benioff seismometer. Photo Credit: Amanda Admire.
USGS Landslide and Liquefaction Ground Failure data products
- Below I present a series of maps that are intended to address the excellent ‘new’ products included in the USGS earthquake pages: landslide probability and liquefaction susceptibility (a.k.a. the Ground Failure data products).
- First I present the landslide probability model. This is a GIS data product that relates a variety of factors to the probability (the chance of) landslides as triggered by this earthquake. There are a number of assumptions that are made in order to be able to produce this model across such a large region, though this is still of great value (like other aspects from teh USGS, e.g. the PAGER alert). Learn more about all of these Ground Failure products here.
- 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). I spend more time discussing landslides and liquefaction in this recent earthquake report.
- This model, like all landslide computer models, uses similar inputs. I review these here:
- Some information about ground shaking. Often, people use Peak Ground Acceleration, though in the past decade+, it has been recognized that the parameter “Arias Intensity” is a better measure of the energy imparted by the earthquake across the land and seascape. Instead of simply accounting for the peak accelerations, AI integrates the entire energy (duration) during the earthquake. That being said, PGA is a more common parameter that is available for people to use. For example, when I was modeling slope stability for the 2004 Sumatra-Andaman subduction zone earthquake, the only model that was calibrated to observational data were in units of PGA. The first order control to shaking intensity (energy observed at any particular location) is distance to the earthquake fault that slipped.
- Some information about the strength of the materials (e.g. angle of internal friction (the strength) and cohesion (the resistance).
- Information about the slope. Steeper slopes, with all other things being equal, are more likely to fail than are shallower slopes. Think about skiing. Beginners (like me) often choose shallower slopes to ski because they will go down the slope slower, while experts choose steeper slopes.
- Areas that are red are more likely to experience landslides than areas that are colored blue. I include a coarse resolution topographic/bathymetric dataset to help us identify where the mountains are relative to the coastal plain and continental shelf (submarine).
- 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.
- The liquefaction susceptibility map for the M 5.6 earthquake did not suggest that there would be possibly much liquefaction from this earthquake (probably due to the small magnitude). I discuss liquefaction more in my earthquake report on the 28 September 20018 Sulawesi, Indonesia earthquake, landslide, and tsunami here.
- Here is a map that shows shaking intensity using the MMI scale (mentioned and plotted in the main earthquake poster maps). I present this here in the same format as the ground failure model maps so we can compare these other maps with the ground shaking model (which is a first order control on slope failure).
Other Report Pages
Some Relevant Discussion and Figures
- Here is a map of the Cascadia subduction zone, modified from Nelson et al. (2006). The Juan de Fuca and Gorda plates subduct norteastwardly beneath the North America plate at rates ranging from 29- to 45-mm/yr. Sites where evidence of past earthquakes (paleoseismology) are denoted by white dots. Where there is also evidence for past CSZ tsunami, there are black dots. These paleoseismology sites are labeled (e.g. Humboldt Bay). Some submarine paleoseismology core sites are also shown as grey dots. The two main spreading ridges are not labeled, but the northern one is the Juan de Fuca ridge (where oceanic crust is formed for the Juan de Fuca plate) and the southern one is the Gorda rise (where the oceanic crust is formed for the Gorda plate).
- This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes.
- Hemphill-Haley, E., 1995. Diatom evidence for earthquake-induced subsidence and tsunami 300 yr ago in southern coastal Washington in GSA Bulletin, v. 107, p. 367-378.
- Nelson, A.R., Shennan, I., and Long, A.J., 1996. Identifying coseismic subsidence in tidal-wetland stratigraphic sequences at the Cascadia subduction zone of western North America in Journal of Geophysical Research, v. 101, p. 6115-6135.
- Atwater, B.F. and Hemphill-Haley, E., 1997. Recurrence Intervals for Great Earthquakes of the Past 3,500 Years at Northeastern Willapa Bay, Washington in U.S. Geological Survey Professional Paper 1576, Washington D.C., 119 pp.
I have compiled some literature about the CSZ earthquake and tsunami. Here is a short list that might help us learn about what is contained within the core that I collected.
- This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. We also can see how a subduction zone generates a tsunami. Atwater et al., 2005.
- Here is an animation produced by the folks at Cal Tech following the 2004 Sumatra-Andaman subduction zone earthquake. I have several posts about that earthquake here and here. One may learn more about this animation, as well as download this animation here.
- Here is a link to the embedded video below, showing the week-long seismicity in April 1992.
- This is the map used in the animation below. Earthquake epicenters are plotted (some with USGS moment tensors) for this region from 1917-2017 with M ≥ 6.5. I labeled the plates and shaded their general location in different colors.
- I include some inset maps.
- In the upper right corner is a map of the Cascadia subduction zone (Chaytor et al., 2004; Nelson et al., 2004).
- In the upper left corner is a map from Rollins and Stein (2010). They plot epicenters and fault lines involved in earthquakes between 1976 and 2010.
- Here is a link to the embedded video below, showing these earthquakes.
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
- 1700.09.26 M 9.0 Cascadia’s 315th Anniversary 2015.01.26
- 1700.09.26 M 9.0 Cascadia’s 316th Anniversary 2016.01.26 updated in 2017 and 2018
- 1992.04.25 M 7.1 Cape Mendocino 25 year remembrance
- 1992.04.25 M 7.1 Cape Mendocino 25 Year Remembrance Event Page
- Earthquake Information about the CSZ 2015.10.08
- 2018.07.24 M 5.6 Gorda plate
- 2018.03.22 M 4.6/4.7 Gorda plate
- 2017.07.28 M 5.1 Gorda plate
- 2016.09.25 M 5.0 Gorda plate
- 2016.09.25 M 5.0 Gorda plate
- 2016.01.30 M 5.0 Gorda plate
- 2015.12.29 M 4.9 Gorda plate
- 2015.11.18 M 3.2 Gorda plate
- 2014.03.13 M 5.2 Gorda Rise
- 2014.03.09 M 6.8 Gorda plate p-1
- 2014.03.23 M 6.8 Gorda plate p-2
- 2018.08.22 M 6.2 Blanco fracture zone
- 2018.07.29 M 5.3 Blanco fracture zone
- 2015.06.01 M 5.8 Blanco fracture zone p-1
- 2015.06.01 M 5.8 Blanco fracture zone p-2 (animations)
- 2018.01.25 M 5.8 Mendocino fault
- 2017.09.22 M 5.7 Mendocino fault
- 2016.12.08 M 6.5 Mendocino fault, CA
- 2016.12.08 M 6.5 Mendocino fault, CA Update #1
- 2016.12.05 M 4.3 Petrolia CA
- 2016.10.27 M 4.1 Mendocino fault
- 2016.09.03 M 5.6 Mendocino
- 2016.01.02 M 4.5 Mendocino fault
- 2015.11.01 M 4.3 Mendocino fault
- 2015.01.28 M 5.7 Mendocino fault
- 2019.06.23 M 5.6 Petrolia
- 2017.03.06 M 4.0 Cape Mendocino
- 2016.11.02 M 3.6 Oregon
- 2016.01.07 M 4.2 NAP(?)
- 2015.10.29 M 3.4 Bayside
- 2018.10.22 M 6.8 Explorer plate
- 2017.01.07 M 5.7 Explorer plate
- 2016.03.19 M 5.2 Explorer plate
- 2017.06.11 M 3.5 Gorda or NAP?
- 2016.07.21 M 4.7 Gorda or NAP? p-1
- 2016.07.21 M 4.7 Gorda or NAP? p-2
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
- Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuju, Y., Eueda, K., and Yamaguchi, D.K., 2005. The Orphan Tsunami of 1700—Japanese Clues to a Parent Earthquake in North America, USGS Professional Paper 1707, USGS, Reston, VA, 144 pp.
- Goldfinger, C., Nelson, C.H., Morey, A., Johnson, J.E., Gutierrez-Pastor, J., Eriksson, A.T., Karabanov, E., Patton, J., Gràcia, E., Enkin, R., Dallimore, A., Dunhill, G., and Vallier, T., 2012 a. Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper # 1661F. U.S. Geological Survey, Reston, VA, 184 pp.
- Dengler, L.A., and McPherson, R.C., 1993. The 17 August 1991 Honeydew Earthquake, North Coast California: A Case for Revising the Modified Mercalli Scale in Sparsely Populated Areas in BSSA, v. 83, no. 4, pp. 1081-1094
- Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
- Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
- Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
- Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
- Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
- 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.
- McCrory, P.A., 2000, Upper plate contraction north of the migrating Mendocino triple junction, northern California: Implications for partitioning of strain: Tectonics, v. 19, p. 11441160.
- McCrory, P. A., Blair, J. L., Oppenheimer, D. H., and Walter, S. R., 2006, Depth to the Juan de Fuca slab beneath the Cascadia subduction margin; a 3-D model for sorting earthquakes U. S. Geological Survey
- 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
- Nelson, A.R., Kelsey, H.M., Witter, R.C., 2006. Great earthquakes of variable magnitude at the Cascadia subduction zone. Quaternary Research 65, 354-365.
- Oppenheimer, D., Beroza, G., Carver, G., Dengler, L., Eaton, J., Gee, L., Gonzalez, F., Jayko, A., Ki., W.H., Lisowski, M., Magee, M., Marshall, G., Murray, M., McPherson, R., Romanowicz, B., Satake, K., Simpson, R., Somerille, P., Stein, R., and Valentine, D., The Cape Mendocino, California, Earthquakes of April, 1992: Subduction at the Triple Junction in Science, v. 261, no. 5120, p. 433-438.
- Patton, J. R., Goldfinger, C., Morey, A. E., Romsos, C., Black, B., Djadjadihardja, Y., and Udrekh, 2013. Seismoturbidite record as preserved at core sites at the Cascadia and Sumatra–Andaman subduction zones, Nat. Hazards Earth Syst. Sci., 13, 833-867, doi:10.5194/nhess-13-833-2013, 2013.
- Plafker, G., 1972. Alaskan earthquake of 1964 and Chilean earthquake of 1960: Implications for arc tectonics in Journal of Geophysical Research, v. 77, p. 901-925.
- Rollins, J.C. and Stein, R.S., 2010. Coulomb stress interactions among M ≥ 5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fault Zone, Cascadia subduction zone, and northern San Andreas Fault: Journal of Geophysical Research, v. 115, B12306, doi:10.1029/2009JB007117, 2010.
- Stein, R.S., Marshall, G.A., Murray, M.H., Balazs, E., Carver, G.A., Dunklin, T.A>, McLaughlin, R.J., Cyr, K., and Jayko, A., 1993. Permanent Ground Movement Associate with the 1992 M=7 Cape Mendocino, California, Earthquake: Implications for Damage to Infrastructure and Hazards to navigation, U.S. Geological Survey Open-File Report 93-383.
- Wang, K., Wells, R., Mazzotti, S., Hyndman, R. D., and Sagiya, T., 2003, A revised dislocation model of interseismic deformation of the Cascadia subduction zone Journal of Geophysical Research, B, Solid Earth and Planets v. 108, no. 1.
References:
Return to the Earthquake Reports page.
This morning (my time) there was a possibly shallow earthquake in western Iran with a magnitude of M = 6.3. This earthquake occurred in the aftershock zone of the 2017.11.12 M 7.3 earthquake. Here is my report for the M 7.3 earthquake. Here are the USGS webpagea for the M 6.3 and M 7.3 earthquakes. 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 ≥ 5.0 in one version.
Simpli”ed map of the Arabian Plate, with plate boundaries, approximate plate convergence vectors, and principal geologic features. Note location of Central Arabian Magnetic Anomaly (CAMA).
Tectonic setting of the Arabian Plate. Red and blue coloured symbols indicate divergence and convergence with overall amount and age, respectively. Green arrows show present-day GPS values with respect to fixed Europa from Iran [21] and white arrow from Oman [22]. a – [23]; b – [20]; c – [18]; d – [19]; e – [14]; f – [15]; g – [8]; h – [16]; i – [17]
Tectonic map of the Zagros Fold Belt showing the position and geometry of the Mountain Front Flexure (MFF). Earthquakes of M ≥ 5 are indicated by small black diamonds. Focal mechanisms from Talebian & Jackson (2004) are also shown, in black (Mw ≥ 5.3) and grey (Mw ≥ 5.3). KH, Khavir anticline; SI, Siah Kuh anticline; ZDF, Zagros Deformation Front.
a) Earthquakes with mb > 5.0 (Jackson and McKenzie, 1984) along seismogenic basement thrusts offset by major strike-slip faults. b) Schematic interpretative map of the main structural features in the Zagros basement. The overall north-south motion of Arabia increases along the belt from NW to SE (arrows with numbers). Central Iran acted as a rigid backstop and caused the strike-slip faults with N-S trends in the west to bulge increasingly eastward. Fault blocks in the north (elongated NW-SE) rotate anticlockwise; while fault blocks in the south (elongated NE-SW) rotate clockwise. c) Simple model involving parallel paper sheets illustrating the observed strike-slip faults in the Zagros. Opening between the sheets (i.e. faults) helped salt diapirs to extrude.
Tectonic map of the Zagros showing the location of the previously published cross-sections with the calculated amount of shortening and the extent of major hydrocarbon fields. The balanced cross-section is marked by the thick black line. M – Mand anticline. Dark grey: Naien-Baft ophiolites (Stöklin, 1968).
Structural cross-sections showing the style of folding across the studied regional transect (see location in Fig. 3). (a) The front of the Zagros Fold Belt along the Anaran anticline above the Mountain Front Flexure (MFF in Emami et al. 2010); (b) the Kabir Kuh anticline, which represents a multi-detachment fold (Vergés et al. 2010); (c) folds developed in the Upper Cretaceous basinal stratigraphy showing much tighter and upright anticlines (modified from Casciello et al. 2009).
The Global Seismic Hazard Map. Peak ground acceleration (pga) with a 10% chance of exceedance in 50 years is depicted in m/s2. The site classification is rock everywhere except Canada and the United States, which assume rock/firm soil site classifications. White and green correspond to low seismicity hazard (0%-8%g), yellow and orange correspond to moderate seismic hazard (8%-24%g), pink and dark pink correspond to high seismicity hazard (24%-40%g), and red and brown correspond to very high seismic hazard (greater than 40%g).
(a) Summary sketch of the tectonic pattern in the Zagros. Overall Arabia–Eurasia motions are shown by the big white arrows, as before. In the NW Zagros (Borujerd-Dezful), oblique shortening is partitioned into right-lateral strike-slip on the Main Recent Fault (MRF) and orthogonal shortening (large gray arrows). In the SE Zagros (Bandar Abbas) no strike-slip is necessary, as the shortening is parallel to the overall convergence. The central Zagros (Shiraz) is where the transition between these two regimes occurs, with anticlockwise rotating strike-slip faults allowing an along-strike extension (black arrows) between Bandar Abbas and Dezful. (b) A similar sketch for the Himalaya (after McCaffrey & N´abˇelek 1998). In this case the overall Tibet-India motion is likely to be slightly west of north. (The India-Eurasia motion is about 020◦, but Tibet moves east relative to both India and Eurasia: Wang et al. 2001). Thrust faulting slip vectors are radially outward around the entire arc (gray arrows). This leads to partitioning of the oblique convergence in the west, where right-lateral strike-slip is prominent on the Karakoram Fault, but no strike-slip in the east, where the convergence and shortening are parallel. The region in between extends parallel to the arc, on normal faults in southern Tibet. (c) A similar sketch for the Java–Sumatra arc, based on McCaffrey (1991). Slip partitioning occurs in the NW, with strike-slip faulting through Sumatra, but not in the SE, near Java. This change along the zone requires the Java–Sumatra forearc to extend along strike.
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.
Significant #earthquake in #Iran, likely an aftershock of the M7.3 Ezgeleh earthquake of November 2017. The difference in focal mechanism reveals slip partitionning in the region. 2 other large strike-slip aftershocks were also recorded last summer pic.twitter.com/P2BOzGI625 — Baptiste Gombert (@BaptisteGomb) November 25, 2018 Mw=6.3, IRAN-IRAQ BORDER REGION (Depth: 10 km), 2018/11/25 16:37:31 UTC – Full details here: https://t.co/YoEYOD1agB pic.twitter.com/u54xzgx8ol — Earthquakes (@geoscope_ipgp) November 25, 2018 strong #earthquake along #Iran #Iraq border, felt #Baghdad, #Kirkuk and #Mosul in Iraq and in #Kermanshah, #Hamadan, #Sulaymaniyah in Iran, even even #Kuwait @LastQuake @Quake_Tracker @JuskisErdbeben @UKEQ_Bulletin pic.twitter.com/NpLVsxxunx — CATnews (@CATnewsDE) November 25, 2018 GFZ moment tensor solution of M6.3 earthquake on Iran-Iraq border https://t.co/ri4JlRyY3K #earthquake pic.twitter.com/VXAO5EdvNO — Aram Fathian (@AramFathian) November 25, 2018 Earthquake in Irak Iran border was widely felt more than 500 km away. Local damage close to the epicentre cannot be excluded, but having struck an area of low population, no widespread damage is expected pic.twitter.com/AaxB5X0ZX8 — EMSC (@LastQuake) November 25, 2018 Mwp6.1 #earthquake Iran – Iraq Border Region 2018.11.25-16:37:34UTC https://t.co/kCIw9Vypa6 — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) November 25, 2018 My thoughts and solidarity to the people affected by #IranEarthquake. Deeply proud of our @Iranian_RCS volunteers and staff, who are ready to support their local communities. pic.twitter.com/Axi1dlRFjQ — Francesco Rocca (@Francescorocca) November 25, 2018 An interesting comparison of the latest M6.3 #Iran #Iraq #earthquake aftershocks and the 2013 #Khanaqin earthquake sequence. Epicenters from IRSC & @IRIS_EPO , focal mechanisms from GFZ pic.twitter.com/xTpds1Ke6V — Sotiris Valkaniotis (@SotisValkan) November 26, 2018 Wrapped interferogram (2.8 cm/1 inch color contours) for M6.3 earthquake near Iran-Iraq border from automatic processing of Copernicus Sentinel-1 SAR by NASA Caltech-JPL ARIA and ESA, with USGS epicenter (star). No sign of surface ruptures, so all fault slip was at depth pic.twitter.com/7eMx6LcpbB — Eric Fielding (@EricFielding) November 26, 2018 #Sentinel1 #InSAR descending interferogram for the M6.3 #Iran #Iraq #earthquake. No clear indications for surface ruptures, most of the slip occured at depth. Processed with DIAPASON at @esa_gep using @CopernicusEU #Sentinel1 data. pic.twitter.com/2Aj9y1759o — Sotiris Valkaniotis (@SotisValkan) November 26, 2018 Simulated coseismic ground deformation map of M6.3 earthquake near Iran/Irap border from our "quickdeform" platform: https://t.co/lrLi8Nrbnt. — Wenbin Xu (@WenbXu) November 27, 2018
Return to the Earthquake Reports page. 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. Well, I was about to head to town and noticed a magnitude M = 5.0 earthquake in Greece. I thought to myself, I wonder if that is a foreshock. It was. 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.
Summary sketch map of the faulting and bathymetry in the Eastern Mediterranean region, compiled from our observations and those of Le Pichon & Angelier (1981), Taymaz (1990), Taymaz et al. (1990, 1991a, b); S¸arogˇlu et al. (1992), Papazachos et al. (1998), McClusky et al. (2000) and Tan & Taymaz (2006). Large black arrows show relative motions of plates with respect to Eurasia (McClusky et al. 2003). Bathymetry data are derived from GEBCO/97–BODC, provided by GEBCO (1997) and Smith & Sandwell (1997a, b). Shaded relief map derived from the GTOPO-30 Global Topography Data taken after USGS. NAF, North Anatolian Fault; EAF, East Anatolian Fault; DSF, Dead Sea Fault; NEAF, North East Anatolian Fault; EPF, Ezinepazarı Fault; PTF, Paphos Transform Fault; CTF, Cephalonia Transform Fault; PSF, Pampak–Sevan Fault; AS, Apsheron Sill; GF, Garni Fault; OF, Ovacık Fault; MT, Mus¸ Thrust Zone; TuF, Tutak Fault; TF, Tebriz Fault; KBF, Kavakbas¸ı Fault; MRF, Main Recent Fault; KF, Kagˇızman Fault; IF, Igˇdır Fault; BF, Bozova Fault; EF, Elbistan Fault; SaF, Salmas Fault; SuF, Su¨rgu¨ Fault; G, Go¨kova; BMG, Bu¨yu¨k Menderes Graben; Ge, Gediz Graben; Si, Simav Graben; BuF, Burdur Fault; BGF, Beys¸ehir Go¨lu¨ Fault; TF, Tatarlı Fault; SuF, Sultandagˇ Fault; TGF, Tuz Go¨lu¨ Fault; EcF, Ecemis¸ Fau; ErF, Erciyes Fault; DF, Deliler Fault; MF, Malatya Fault; KFZ, Karatas¸–Osmaniye Fault Zone.
GPS horizontal velocities and their 95% confidence ellipses in a Eurasia-fixed reference frame for the period 1988–1997 superimposed on a shaded relief map derived from the GTOPO-30 Global Topography Data taken after USGS. Bathymetry data are derived from GEBCO/97–BODC, provided by GEBCO (1997) and Smith & Sandwell (1997a, b). Large arrows designate generalized relative motions of plates with respect to Eurasia (in mm a21) (recompiled after McClusky et al. 2000). NAF, North Anatolian Fault; EAF, East Anatolian Fault; DSF, Dead Sea Fault; NEAF, North East Anatolian Fault; EPF, Ezinepazarı Fault; CTF, Cephalonia Transform Fault; PTF, Paphos Transform Fault; CMT, Caucasus Main Thrust; MRF, Main Recent Fault.
Schematic map of the principal tectonic settings in the Eastern Mediterranean. Hatching shows areas of coherent motion and zones of distributed deformation. Large arrows designate generalized regional motion (in mm a21) and errors (recompiled after McClusky et al. (2000, 2003). NAF, North Anatolian Fault; EAF, East Anatolian Fault; DSF, Dead Sea Fault; NEAF, North East Anatolian Fault; EPF, Ezinepazarı Fault; CTF, Cephalonia Transform Fault; PTF, Paphos Transform Fault.
Simplified map showing the main structural features along the Hellenic arc and trench system, as well as the main active structures in the Aegean area. The mean GPS horizontal velocities in the Aegean plate, with respect to a Eurasia-fixed reference frame, are shown (after Kahle et al., 1998; McClusky et al., 2000). The lengths of vectors are
General simplified structural map of Greece showing the main currently active structures in the five structural regions along the Hellenic Arc, as well as some main pre-existing lineaments. Insets illustrate the main structural features of each region and the period of activity of these structures (for further details see discussion). KFZ—Kefallonia Fault zone; MCL—Mid-Cycladic lineament; NAFZ—North Anatolia fault zone; NAT—North Aegean trough; PF—Pelagonian fault.
Schematic structural map of the central Hellenic Peninsula (Region II), with stress nets showing the orientation of principal stress axes. Stress net explanation as for Figure 3. Also included are cross-sections showing the geometry and kinematics of the External Hellenides in the area (A-A′) and the evolution of the synorogenic basin in the Paleros area (B-B′-B′′). AG—Abelon graben; ALG—Almyros graben; AMG—Amvrakikos graben; CG—Corinth graben; KB—Kymi basin; KF—Klenia fault zone; KFZ—Kefalonia fault zone; LF—Lapithas fault; MG—Megara graben; NG—Nedas graben; P—Parnitha area; PG—Pyrgos graben; PLB—Paleros basin; PTG—Patras graben; RG—Rio graben; S-A.G— Sperchios-Atalanti graben; SEG—South Evoikos graben; TB—Thiva basin; TG—Tithorea graben; TRG—Trihonis graben; VF—Vounargos 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.
M6.8 #earthquake was a truly international quake felt up to 800 km in at least 8 countries (Malta, Libya, Italy, Greece, Macedonia, Albania, Bosnia, Bulgaria, Turkey) pic.twitter.com/gt2oVn5tLS — EMSC (@LastQuake) October 26, 2018 Todays strong #earthquake in Ionian Sea, #Greece, in an area of high seismicity near the junction of Hellenic Arc subduction and Cephalonia Transform Fault. NW-SE/WNW-ESE thrusting in accord. with local tectonic structures. Revised epicenter location (ML 6.4) from NOA. pic.twitter.com/0aqZhsTwOb — Sotiris Valkaniotis (@SotisValkan) October 26, 2018 Sea level changes following M6.8 earthquake are still being observed. Their amplitude remain hopefully limited. Do not go checking your boats there may be strong currents in harbors pic.twitter.com/0WGNjZGnd2 — EMSC (@LastQuake) October 26, 2018 Mw=7.0, IONIAN SEA (Depth: 15 km), 2018/10/25 22:54:51 UTC – Full details here: https://t.co/jXsx6jWEC9 pic.twitter.com/pZiAZvPeKx — Earthquakes (@geoscope_ipgp) October 25, 2018 strong #earthquake offshore Western #Greece near #Zakynthos, also felt in Southern #Italy and #Albania @LastQuake @Quake_Tracker @JuskisErdbeben pic.twitter.com/BF8W44NOjq — CATnews (@CATnewsDE) October 25, 2018 potential #tsunami after #earthquake offshore #Greece, still uncertain, yet a run-up of up to 1.5m can be possible locally, but mostly expected peak coastal wave heights of 20-50cm in Western Greece @LastQuake @JuskisErdbeben @Quake_Tracker4 pic.twitter.com/cejAwCoGgD — CATnews (@CATnewsDE) October 25, 2018 A 6.9 magnitude earthquake took place in Greece today. The epicenter of the quake was reported to be in the Iyon Sea, 250 km west to Athens. Users shared footage on social media of the quake, that happened in a depth of 16.6 km. pic.twitter.com/p4VrGUXT9y — EHA News (@eha_news) October 25, 2018 Faulting mechanism for the M6.8 Greece earthquake (blue beach ball; from the USGS) has a complex oblique mechanism. Past quakes in the area related to the Hellenic subduction thrust. The Cephalonia strike-slip fault lies a little further to the north. Tectonically complex region. pic.twitter.com/asklvRpB7V — Stephen Hicks 🇪🇺 (@seismo_steve) October 25, 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. We continue to learn more each day as people collect additional information. Here is my initial Earthquake Report for this M 7.5 Donggala Earthquake. In short, there was an earthquake with magnitude M = 7.5 on 2018.09.28. Minutes after the earthquake there was a tsunami that hit the coasts of Palu Bay. Possibly during the earthquake, kilometer scale landslides were triggered along the floor of Palu Valley. These three natural disasters would be devastating on their own, but when considered in their totality, this trifecta has led to considerable suffering in central Sulawesi, Indonesia. I will attempt to summarize some of what we have learned in the past couple of weeks. I will begin with the earthquake observations, then discuss the tsunami and landslides. The M=7.5 Donggala earthquake struck along the most active and seismically hazardous fault on the island of Sulawesi (Celebes), Indonesia. The Palu-Koro fault has a slip rate of 42 mm per year (Socquet et al., 2006), has a record of M=7-8 prehistoric earthquakes (Watkinson and Hall, 2017), as well as a record of M>7 earthquakes in the 20th century (Gómez et al., 2000). The seismic hazard associated with this fault was well evidenced prior to the earthquake (Cipta et al., 2016). According to the National Disaster Management Authority (Badan Nasional Penanggulangan Bencana, BNPB), there were around 2.4 million people exposed to earthquake intensity MMI V or greater. The Modified Mercalli Intensity (MMI) scale is a measure of how strongly the ground shaking is from an earthquake. MMI V is described as, “Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.” However, the closer one is to the earthquake source, the greater the MMI intensity. There have been reported observations as large as MMI VIII. 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. Perhaps some of the most phenomenal results from remote sensing analyses are coming from the work of Dr. Sotiris Valkaniotis. Dr. Valkaniotis has been using the open source softare mic-mac to compare pre- and post-earthquake satellite imagery. I will call this “pixel matching” analysis, or optical analysis. Pixels are “picture elements” that comprise what a raster is created out of. Consider a television or computer monitor. The screen is displaying rows and columns of colored light. Each cell of this “raster” display is called a pixel. Basically, the software compares the patterns in the compared imagery to detect changes. If a group of pixels in the image move relative to other pixels, then this motion is quantified. This type of analysis is particularly useful for strike-slip earthquakes as the ground moves side by side. Dr. Valkniotis has used a variety of imagery types. Below are a couple products that they have shared on social media. Please contact Dr. Valkaniotis for more information!
Landsat-8 pixel tracking results (old school with Ampcor!) show a nice stepover in the Indonesia earthquake. This event gives a good perspective on why the valley in which Palu rests even exists in the first place
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. Line-of-sight deformation from ALOS-2 for the Palu earthquake (data provided by JAXA, processed using GMTSAR). Unwrapping is challenging for this earthquake! Some near-fault region is too decorrelated to be trustworthy.
#InSAR map of range or line-of-sight deformation of #PaluEarthquake from NASA Caltech-JPL analysis of JAXA ALOS-2 PALSAR-2 data acquired last week. Red areas moved west or down in this unwrapped interferogram, unreliable phase masked out. Star USGS epicenter.
#InSAR map of range or line-of-sight deformation of #PaluEarthquake from NASA Caltech-JPL analysis of JAXA ALOS-2 PALSAR-2 data acquired last week. Red areas moved west or down in this unwrapped interferogram, unreliable phase masked out. Star USGS epicenter.
There have been observations of tsunami waves recorded by tide gages installed at Pantoloan Port and Mumuju, Sulawesi. Locations are shown on the map above. A tsunami with a 10 cm wave height was recorded at Mumuju tide gage and a wave with a height of about 1.7 meters was recorded at Pantoloan tide gage. Learn more about the tsunami here. Here is my plot of the Pantoloan Port tide gage. 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. While remote sensing methods are useful to locate damage in the region, field observations will be key in the effort to analyze the landscape response to these natural disasters. The Indonesian government and international researchers are already surveying the region and collecting these important observational details. 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. A lateral spread is a translational landslide that occurs over gentle slopes or flat terrain. The failure surface is more planar and less curvy than for rotational slides. The spread is usually caused when a confined layer of sediment is transformed from a solid into a liquid state. In the lateral spread figure below, it is the water that exists in the “silt and sand” deposits that has an increase in pore pressure to generate liquefaction, causing the failure. The overlying sediment is more cohesive, which is why we may have seen landslides move as coherent blocks across the landscape. However, these landslide blocks may disaggregate as they move, sometimes turning into a flow. This entire range of behavior can be seen in the post-earthquake aerial imagery of Palu Valley. 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 has been a large amount of videos posted online via social media and professional news organizations showing the impact of these landslides. Perhaps one of the best places to seek an expert informed view of landslide processes, of all types, is from Dr. David Petley and his blog, The Landslide Blog. Petley has presented a couple summaries of these observations of coseismic (during the earthquake) landslides as triggered by ground shaking from the M=7.5 Donggala earthquake. The company Digital Globe provides high resolution satellite imagery for a fee, but they distribute imagery for free via their open data program following natural disasters. This imagery is available for noncommercial use including disaster impact analysis. Many of the preliminary analyses of impact presented on social media by subject matter experts has been based upon this imagery. Another source of fee based imagery is from Planet Lab that also provides imagery in support of peoples’ response to natural disasters via their disaster data program. Most of the entire Palu Valley has previously been mapped as susceptible to liquefaction due to (1) the underlying materials are sediments and (2) a shallow ground water table (lots of water in the sediment, reaching close to the ground surface). The northern part of the valley is a river delta full of loose and water saturated sediments. Yet, only a small portion of the entire valley failed as these km scale lateral spreads. Why is this? This is probably due to a combination of factors, but the biggest factor may be the heterogeneity of the underlying earth materials. These sediments probably have variation in material properties: strength (“angle of internal friction“), stickiness (“cohesion“), and porosity (spaces between sediment particles that can be filled with water). Below is the liquefaction susceptibility map prepared in 2012. I just noticed that one of the 2 largest landslides actually happened outside of these liquefaction zones. It is also possible that the earthquake intensity (ground shaking and seismic wave energy), that was directed in different directions, may have caused different amounts of “seismic loading” of these slopes. Knowing how these material properties vary spatially is difficult to know as the materials in the subsurface are generally not in plain view (buried under ground). People can drill and sample the material properties (an engineering geologist) and then calculate the strength of these materials (engineer) on a site by site basis. 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.
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.
Just a few hours ago there was a subduction zone megathrust earthquake along the New Britain Trench in the western equatorial Pacific Ocean. 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 ≥ 7.5 in one version.
Topography, bathymetry and regional tectonic setting of New Guinea and Solomon Islands. Arrows indicate rate and direction of plate motion of the Australian and Pacific plates (MORVEL, DeMets et al., 2010); Mamberamo thrust belt, Indonesia (MTB); North Fiji Basin (NFB).
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.
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.
Subduction megathrust earthquake preceded by a foreshock | https://t.co/1twVj9WIVY https://t.co/POB7EYPoXv via #NSFfunded @temblor #temblor #Earthquake — temblor (@temblor) October 11, 2018 First motion mechanism: Mwp7.0 #earthquake New Britain Region, PNG https://t.co/kCIw9Vypa6 pic.twitter.com/bAgtrI8GrD — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) October 10, 2018 Mw=7.0, NEW BRITAIN REGION, P.N.G. (Depth: 48 km), 2018/10/10 20:48:20 UTC – Full details here: https://t.co/u8ZsZMvQD6 pic.twitter.com/UXRjuSJVOK — Earthquakes (@geoscope_ipgp) October 10, 2018 … and then two more M6 aftershocks about 10min and 25min after the M7.0 eventhttps://t.co/1BF5xJVFGQ pic.twitter.com/qzfsSq9iec — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) October 10, 2018
Return to the Earthquake Reports page. 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. 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. Based on what we know about strike-slip fault earthquakes, the portions of the fault to the north and south of today’s sequence may have an increased amount of stress due to this earthquake. Stay tuned for a Temblor.net report about this earthquake where I discuss this further. There are reports of a local tsunami with a run-up about 2 meters. However, the UNESCO Sea Level Monitoring Facility (website) does not show any tsunami observations on tide gage data in the region. 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. Did you feel this earthquake? If so, fill out the USGS “Did You Feel It?” form here. If not, why not? Probably because you were too far away. The closer to an earthquake, the more strong the shaking intensity and the larger chance of infrastructure damage (roads, houses, etc.). The USGS PAGER alert for this earthquake shows that there are ~282,000 people living in Palu, a city near the epicenter. The estimate for shaking intensity is a MMI VI, which could result in light damage for resistant structures and moderate damage for vulnerable structures. More about USGS PAGER alerts here. There exists a possibility that there were more than 100 fatalities from this earthquake. I awakened this morning (my time, obviously) to find that there are over 380 reported deaths from this earthquake and tsunami. More on this later in the day (clouds are preparing to our and i need to put some of my stuff under tarps). I prepared a report for Temblor where we present results of static coulomb stress modeling. Here is that report. Here is a (200 MB) video that I edited slightly. Download here. This was originally posted here. 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. I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.
Regional geodynamic sketch that presents the present day deformation model of Sulawesi area (after Beaudouin et al., 2003) and four main deformation systems around the Central Sulawesi block, highlighting the tectonic complexity of Sulawesi. Approximate location of the Central Sulawesi block rotation pole (P) [compatible with both GPS measurements (Walpersdorf et al., 1998a) and earthquake moment tensor analyses (Beaudouin et al., 2003)], as well as the major active structures are reported. Central Sulawesi Fault System (CSFS) is formed by the Palu–Koro and Matano faults. Arrows correspond to the compression and/or extension directions deduced from both inversion and moment tensor analyses of the focal mechanisms; arrow size being proportional to the deformation rate (e.g., Beaudouin et al., 2003).We also represent the focal mechanism provided by the Harvard CMT database [CMT data base, 2005] for the recent large earthquake (Mw=6.2; 2005/1/23; lat.=0.92° S; long.=120.10° E). The box indicates the approximate location of the Fig. 6 that corresponds to the geological map of the Palu basin region. The bottom inset shows the SE Asia and Sulawesi geodynamic frame where arrows represent the approximate Indo-Australian and Philippines plate motions relative to Eurasia.
Sketch map of the Cenozoic Central Sulawesi fault system. ML represents the Matano Lake, and Leboni RFZ, the Leboni releasing fault zone that connects the Palu–Koro and Matano Faults. Triangles indicate faults with reverse component (triangles on the upthrown block). On this map are reported the fault kinematic measurement sites.
West-looking view of the Palu–Koro fault escarpment SSW of the Palu basin showing faceted spurs and a left-lateral offset of an alluvial fan. At the bottom, sketch of the photograph where white arrows point to the fault trace and black arrows point to the cumulate fan offset along the fault traces.
Simplified geological map of the Palu domain (modified after Sukamto, 1973) where are reported the locations of fission-track samples. 1 — Holocene alluvial deposits; 2 — Quaternary coral reef terraces; 3 — Mio-quaternary molasses, 4 — Mio-quaternary granitic rocks and granodiorites, 5 — Middle to Upper Eocene Tinombo Formation metamorphism, 6 — Tinombo Formation magmatism, 7 and 8 — metamorphic bedrock (7 — Cretaceous Latimonjong Formation; 8 — Triassic-Jurassic Gumbasa Formation).
The area of convergence of the Eurasian, Philippine and Australian plate is characterized by the Sula block motion. Active block boundaries are the North Sulawesi trench *(1)., the Palu-Koro (2), and the Matano (3) faults. The Palu transect is indicated buy the box, with a zoom presented in the inset. Furthermore, the two largest earthquakes (CMT) occurring during the observation period are indicated.
Velocities of the Palu transect stations, with respect to the PALU station. Error ellipses correspond to formal uncertainties of the global solution with a confidence level of 90%.
Transect station velocity components parallel to the fault, with the co-seismic deformation due to the Jan. 1996 earthquake removed. They are indicated in function of their distance to the fault. The dark grey line shows best model values (5.5 cm/yr total velocity, 12 km locking depth). Lighter grey lines correspond to locking depths of 8 and 16 km, marking an uncertainty of +-4 km.
GPS velocities of Sulawesi and surrounding sites with respect to the Sunda Plate. Grey arrows belong to the Makassar Block, black arrows belong to the northern half of Sulawesi, and white arrows belong to non-Sulawesi sites (99% confidence ellipses). Numbers near the tips of the vectors give the rates in mm/yr. The main tectonic structures of the area are shown as well.
Rotational part of the inferred velocity field in the Sulawesi area (relative to the Sunda Plate) as predicted by the Euler vectors of the best fit model (model 2). Error ellipses of predicted vectors show the 99% level of confidence. Also shown are poles of rotation and error ellipses (with respect to the Sunda Plate) from the best fit model. Curved arrows indicate the sense of rotation, and numbers indicate the rotation rate. MAKA, Makassar Block; MANA, Manado Block; ESUL, East Sula Block; NSUL, North Sula Block.
Best fit block model derived from both GPS and earthquakes slip vector azimuth data. Center: Observed (red) and calculated (green) velocities with respect to the Sunda Block (shown are 20% confidence ellipses, after GPS reweighting; see text). The slip rate deficit (mm/yr) for the faults included in the model is represented by a color bar. The profile of Figure 7 is located by the dashed black line. The black rectangles around Palu and Gorontalo faults localize the insets. Top right and bottom left insets show details of the measured and modeled velocities across the Gorontalo and Palu faults. The bottom right inset shows residual GPS velocities with respect to the model. The value of the coupling ratio, j, for the faults included in the model is represented by the color bar. Light blue dots represent the locations of the fault nodes where the coupling ratio is estimated. Nodes along the block boundaries are at the surface of the Earth, and the others are at depth along the fault plane. In this model, j is considered uniform along strike and depth for all the faults, except for Palu Fault and Minahassa Trench, where it is allowed to vary along strike.
Velocity profile across Makassar Trench, Palu Fault, and Gorontalo Fault (profile location in Figure 6) in Sunda reference frame. Observed GPS velocities are depicted by dots with 1-sigma uncertainty bars, while the predicted velocities are shown as curves. The profile normal component (approximately NNW) (i.e., the strike-slip component across the NW trending faults) is shown with black dots and solid line, while the profile-parallel component (normal or thrust component across the fault) is shown with grey dots and a dashed line. Where the profile crosses the faults and blocks is labeled.
(top) GPS velocities in Palu area relative to station WATA. STRM topography is used as background. (bottom) Four parallel elastic dislocations that fit best the velocities in the Palu fault zone. The fault-parallel component of the GPS velocities (with 1-sigma error bars) is plotted with respect to their distance to the main fault scarp, in the North Sula Block reference frame. The black curve represents the fault-parallel modeled velocity of the four strand model. For comparison, the fault-parallel modeled velocity predicted by the single fault model is also plotted (grey dashed curve). The location of the modeled dislocation is represented as vertical bars for each model (black and dashed grey lines, respectively).
Central Sulawesi overview digital elevation model (SRTM), CMT catalogue earthquakes, 35 km depth and structures that show geomorphic evidence of Quaternary tectonic activity. Rivers marked in white. Illumination from NE.
(a) The Palu and Sapu valleys showing structures that with geomorphic evidence of Quaternary tectonic activity, plus topography and drainage. Mountain front sinuosity values in bold italic text. For location, see Figure 4. Major drainage basins for Salo Sapu and Salo Wuno are marked, separated by uplift at the western end of the Sapu valley fault system. (b) View of the Palu–Koro Fault scarp from the Palu valley, showing geomorphic evidence of Quaternary tectonic activity.
Evidence of a cross-basin fault system within the Palu valley Quaternary fill. (a) Overview ASTER digital elevation model draped with ESRI imagery layer. Illumination from NW. Palu River channels traced from six separate images from 2003 to 2015. Inset shows fault pattern developed in an analogue model of a releasing bend, modified after Wu et al. (2009), reflected and rotated to mimic the Palu valley. Sidewall faults and cross-basin fault system are highlighted in the model and on the satellite imagery. (b, c) Laterally confined meander belts, interpreted as representing minor subsidence within the cross-basin fault system. (d) Laterally confined river channels directly along-strike from a Palu–Koro Fault strand seen to offset alluvial fans in the south of the valley. (c, d, e) showESRI imagery.
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.
#Earthquake_alert [UPDATE] – The spread of #epicenters of #Donggala #earthquake on Sep 28, 2018. Map obtained from EMSC App with a slight modification. C.c. @EricFielding @seismo_steve @patton_cascadia @janinekrippner #Indonesia #earthquake #alert #warning #mitigation #Sulawesi pic.twitter.com/NOMPtBBr1B — Desianto F. Wibisono (@TDesiantoFW) September 28, 2018 BREAKING: Video shows tsunami hitting the Indonesian city of Palu pic.twitter.com/XCXXHZwAtu — BNO News (@BNONews) September 28, 2018 This footage shows the catastrophic moment when #tsunami hit the city of Palu after 7.7 magnitude #earthquake shook the city this evening. #prayforpalu #prayforindonesia pic.twitter.com/I8JBi4dZjz — Ramadhani Eko P (@ramadhaniep) September 28, 2018 First motion mechanism: Mwp7.2 #earthquake Minahassa Peninsula, Sulawesi https://t.co/kCIw9Vypa6 pic.twitter.com/PAAwEM8mGX — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 28, 2018 News on major western channels is starting to show up… 4 hours after the earthquake…https://t.co/lcm521Hx1f — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 28, 2018 Source model by @geoscope_ipgp @IPGP_officiel confirms magnitude (Mw7.5) and left-lateral strike-slip mechanism for #earthquake on Palu-Koro FZ #Sulawesi, #Indochina. Hypocenter depth estimate 18-25km.https://t.co/4AvAbHbo4Q pic.twitter.com/G22EAbo5Bc — Robin Lacassin (@RLacassin) September 28, 2018 Left lateral movement along the Palu-Koro fault shown by GPS (figure from Walpersdorf et al. 1998) consistent with NNW nodal plane of Mw 7.4 mainshock focal mechanism. pic.twitter.com/i0Cid1jIyl — JD Dianala (@geoloJD) September 28, 2018 Back Projection for Mw 7.5 MIZAHASSA PENINSULA #EARTHQUAKE, SULAWESI https://t.co/wxc1fnAGWQ #SulawesiTengah pic.twitter.com/RdEfD50Xkz — IRIS Earthquake Sci (@IRIS_EPO) September 28, 2018 Its so close to my city. After earthquakes then we attack by tsunami again. Please pray for us :( #PrayForDonggala #Gempa pic.twitter.com/9Q7fWBuOer — ★ ghy ★ (@ksjnoona) September 28, 2018 Interesting difference between locations of aftershocks of M7.5 Palu earthquake in black and the foreshocks in purple pic.twitter.com/hO7wGh8Cq6 — Jascha Polet (@CPPGeophysics) September 28, 2018 Analisis sementara ahli tsunami dsri ITB berdasarkan modeling dan kajian sebelumnya bahwa tsunami di Palu disebabkan adanya longsoran bawah laut saat gempa 7,7 SR mengguncang Donggala. Teluk Palu dan pesisir Donggala memang rawan tsunami. Masih dilakukan kajian lagi. pic.twitter.com/1YbHEFmTfT — Sutopo Purwo Nugroho (@Sutopo_PN) September 29, 2018 Potential #tsunami impact #Palu, #Minahasa, #Sulawesi, after very strong #earthquake. Based on adjusted @USGS finite fault model and video footage. Numerical model, no observation(!) Any news on wave heights around #Baya or #Mapaga? @UKEQ_Bulletin @JuskisErdbeben @patton_cascadia pic.twitter.com/jF5DP4saL9 — CATnews (@CATnewsDE) September 28, 2018 Analisis sementara ahli tsunami dsri ITB berdasarkan modeling dan kajian sebelumnya bahwa tsunami di Palu disebabkan adanya longsoran bawah laut saat gempa 7,7 SR mengguncang Donggala. Teluk Palu dan pesisir Donggala memang rawan tsunami. Masih dilakukan kajian lagi. pic.twitter.com/1YbHEFmTfT — Sutopo Purwo Nugroho (@Sutopo_PN) September 29, 2018 M7.5 #earthquake and #aftershocks in #Indonesia as detected by the #RaspberryShake #CitizenScience community network. See https://t.co/hbr1xPdgFN and https://t.co/iYdJRU3iub for more details. #Palu #Sulawesi #Philippines #Malaysia pic.twitter.com/WskgV2VNiK — Raspberry Shake (@raspishake) September 28, 2018 I am pretty sure the #tsunami video is at -0.8821, 119.841 – see images. This is part of the waterfront at #Palu. If I am right, and assuming the video was shot today, then it appears that we have a significant tsunami at this location at least. pic.twitter.com/J6boTUrrcm — Dave Petley (@davepetley) September 28, 2018 Donggala as a 7.7 magnitude #earthquake with #tsunami warning occured recently in north of #Palu Sulawesi . #PrayForDonggala 🙏🏼🇮🇩 pic.twitter.com/vcx83UtOlC — Zabihullah Najafi (@zabinajafi) September 28, 2018 Full Video. Semoga Allah SWT memberikan keselamatan dan ketabahan untuk saudara-saudara kita di Sulawesi Tengah. 🙏🏼 — Anggunesia (@Anggunesia) September 28, 2018 #Palu before and after tsunami pic.twitter.com/MdxICg2oC0 — ROBERT VINOD (@RobertVinod) September 28, 2018 Jembatan Palu IV destroyed by the earthquake in #Palu, Central Sulawesi.#gempa #tsunami pic.twitter.com/Q8PKwvE5Hj — Matthew Lanier (@PakMamat) September 28, 2018 Incredible and scary #tsunami video from #Palu, #Indonesia Through google maps I found where it was shot as multiple tsunami waves funneled north to south down a long narrow bay into Palu Shopping district on the beach. Devastating and tragic pic.twitter.com/RIogOlP0IR — Michael Seger (@MichaelSeger) September 28, 2018 Our prayers are always with #Indonesia May Allah help all the brothers and sisters who are suffering because of #earthquake and #tsunami which happened few hours ago. #palu #donggala #prayfordonggala pic.twitter.com/gdVzzMZ6uF — M.Abdulhakim Mahmout (@ahmahmout) September 28, 2018 Another video at moment of #Sunami at #Palu #Sulawesi in Indonesia — Andrea Legarreta (@AndeaLegarreta) September 28, 2018 In a video that appeared to be taken at night, doctor Komang Adi Sujendra said 30 people were killed and had been taken to the hospital.https://t.co/I4fko9mvwo#Quake #Indonesia #Palu #Sulawesi #Tsunami — New Straits Times (@NST_Online) September 29, 2018 The Indonesian news-agency Kompas, states that the Agency for Meteorology, Climatology and Geophysics (BMKG) has said that a 1.5-2m. #Tsunami have hit the areas of #Palu #donggala and #Mamuju — Øystein L. Andersen (@OysteinLAnderse) September 28, 2018 Amazing! Did surface fault rupture pass under (and destroy) Palu Bridge IV? Apparent left-lateral offset of bridge ~~5m in still from video. M7.5 #earthquake #Palu #Indonesiahttps://t.co/Oirdl1oOPE pic.twitter.com/8licQbUufz — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) September 29, 2018 Earthquake triggering a tsunami and likely more shocks in Indonesia | https://t.co/1twVj9F84q https://t.co/tChjMILSd9 via #NSFfunded @temblor #earthquakes #temblor — temblor (@temblor) September 29, 2018 Kondisi jembatan Ponulele di Kota Palu yang hancur akibat gempa 7,7 SR. Jembatan ini sebelumnya sebagai icon Kota Palu. Kondisinya hancur. Pascagempa tsunami menerjang pantai sekitarnya. Permukiman di bawah hancur dan terbawa tsunami. pic.twitter.com/4XrLrzHp1a — Sutopo Purwo Nugroho (@Sutopo_PN) September 28, 2018 BBC News – Indonesia earthquake: Hundreds dead in Palu quake and tsunami https://t.co/r4qnOv6Be6 — patton_cascadia (@patton_cascadia) September 29, 2018 SITUATION UPDATE No. 1 – Sulawesi Earthquake – 29 September 2018 – Our deepest condolences for the affected communities in Sulawesi especially in #Donggala and #Palu. Stay tuned to official channels for further information https://t.co/2dLFwj3Crw … #bnpb #gempa #tsunami pic.twitter.com/toJ08oKBr8 — AHA Centre (@AHACentre) September 29, 2018 From colleagues in #Palu #centralsulawesi following yesterday’s #earthquake and #tsunami 🙏😢 pic.twitter.com/p451qx3ELq — Richard Woods (@RichardWoodsNZ) September 29, 2018 #Peringatan Dini Tsunami di SULTENG,SULBAR, Gempa Mag:7.7, 28-Sep-18 17:02:44WIB, Lok:0.18LS,119.85BT,Kdlmn:10Km#BMKG pic.twitter.com/V9FLnJbdhs — BMKG (@infoBMKG) September 28, 2018 Zoomed in around shoreline. pic.twitter.com/nMJ7oICQmE — Murray Ford (@mfordNZ) September 29, 2018 Quick & rough subpixel optical correlation for images above, using MicMac (no scale or georef), 2D displacement on NS axis. Red is movement towards north, blue towards south. pic.twitter.com/ueUbVxT4Qe — Sotiris Valkaniotis (@SotisValkan) September 29, 2018 From colleagues in #centralsulawesi following yesterday’s #earthquake and #tsunami 🙏😢 #Palu #Donggala pic.twitter.com/hit2B7ZD7V — Richard Woods (@RichardWoodsNZ) September 29, 2018 Aerial photos of #tsunami and #earthquake damage in #Palu have been released by #Indonesia's disaster management agency @BNPB_Indonesia pic.twitter.com/vXtGxa8UZx — Richard Woods (@RichardWoodsNZ) September 29, 2018 Aerial photos of #tsunami and #earthquake damage in #Palu have been released by #Indonesia's disaster management agency @BNPB_Indonesia pic.twitter.com/nhxoPk27Rj — Richard Woods (@RichardWoodsNZ) September 29, 2018 Perhatikan baik² video pasca Gempa Sulawesi ini. Ada 4 point yg bisa kita liat, utk menilai betapa bikin merindingnya dampak gempa ini pic.twitter.com/rFvtnzotIs — Eling Lan Waspada (@Jogja_Uncover) September 29, 2018
Back to the Earthquake Reports page. The earthquakes continue, every day. Today, there was a large earthquake associated with the subduction zone that forms the Kermadec Trench. 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. This is my first earthquake report to utilize the new slab contours (Slab 2.0) from Hayes (2018). There has been a recent sequence of ultra deep earthquakes in the Fiji region, as well as subduction zone related earthquakes along the southern New Hebrides Trench. These links lead to my earthquake reports for those two regions: Fiji and New Hebrides. 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 the Southwest Pacific Ocean showing the regional tectonic setting and location of the two dredged profiles. Depth contours in kilometres. The presently active arcs comprise New Zealand–Kermadec Ridge–Tonga Ridge, linked with Vanuatu by transforms associated with the North Fiji Basin. Colville Ridge–Lau Ridge is the remnant arc. Havre Trough–Lau Basin is the active backarc basin. Kermadec–Tonga Trench marks the site of subduction of Pacific lithosphere westward beneath Australian plate lithosphere. North and South Fiji Basins are marginal basins of late Neogene and probable Oligocene age, respectively. 5.4sK–Ar date of dredged basalt sample (Adams et al., 1994).
Large subduction-zone interplate earthquakes (large open gray stars) labeled with event date, Mw, GCMT focal mechanisms, and GPS velocity vectors (gray arrows and black triangles labeled with station name). GPS velocities are listed in Table 3. Black lines indicate the Tonga–Kermadec and Vanuatu trenches. Note that the 2009/09/29 Samoa–Tonga outer trench-slope event (Mw 8.1) triggered large interplate doublets (both of Mw 7.8; Lay et al., 2010). The Pacific plate subducts westward beneath the Australian plate along the Tonga–Kermadec trench, whereas the Australian plate subducts eastward beneath the Vanuatu arc and North Fiji basin. The opposite orientation between the Tonga–Kermadec and Vanuatu subduction systems is due to complex and broad back-arc extension in the Lau and North Fiji basins (Pelletier et al., 1998).
Regional map of moderate-sized (mb > 4:7) shallow-focus repeating earthquakes and background seismicity along the (a) Tonga–Kermadec and (b) Vanuatu (former New Hebrides) subduction zones. Shallow repeating earthquakes (black stars) and their available Global Centroid Moment Tensor (GCMT; Dziewoński et al., 1981; Ekström et al., 2003) are labeled with event date and doublet/cluster id where applicable. Colors of GCMT are used to distinguish nearby different repeaters. Source parameters for the clusters and doublets are listed in Tables 1 and 2. Background seismicity is shown as gray dots and large interplate earthquakes (moment magnitude, Mw > 7:3) since 1976 are shown as large open gray stars. Black lines indicate the trench (Bird, 2003) and slab contour at 50-km depth (Gudmundsson and Sambridge, 1998). Repeating earthquake clusters in the (a) T1 and T2 plate-interface regions in Tonga and (b) V3 plate-interface region in Vanuatu are used to study the fault-slip rate ( _d). A regional map of the Tonga–Kermadec–Vanuatu subduction zones is
Earthquakes and subducted slabs beneath the Tonga–Fiji area. The subducting slab and detached slab are defined by the historic earthquakes in this region: the steeply dipping surface descending from the Tonga Trench marks the currently active subduction zone, and the surface lying mostly between 500 and 680 km, but rising to 300 km in the east, is a relict from an old subduction zone that descended from the fossil Vitiaz Trench. The locations of the mainshocks of the two Tongan earthquake sequences discussed by Tibi et al.2 are marked in yellow (2002 sequence) and orange (1986 series). Triggering mainshocks are denoted by stars; triggered mainshocks by circles. The 2002 sequence lies wholly in the currently subducting slab (and slightly extends the earthquake distribution in it),whereas the 1986 mainshock is in that slab but the triggered series is located in the detached slab,which apparently contains significant amounts of metastable olive.
A schematic diagram illustrating the slab–plume interaction beneath the Tonga–Kermadec arc. Cyan lines on the surface show trenches, as shown in Fig. 1. HP, Hikurangi Plateau; KT, Kermadec Trench; NHT, New Hebrides Trench; TT, Tonga Trench; VT, Vitiaz Trench. The Samoan plume originates from a Mega ULVZ at the core–mantle boundary (CMB). The buoyancy caused by large stress from the plume at the bottom of the Tonga slab may contribute to the slab stagnation within the mantle transition zone, while the Kermadec slab is penetrating into the lower mantle directly. At the northern end of the Tonga slab, plume materials migrate into the mantle wedge, facilitated by strong toroidal flow around the slab edge induced by fast slab retreat
Boundaries (heavy colored lines) of the New Hebrides (NH), Balmoral Reef (BR), Conway Reef (CR), and Futuna (FT) plates. All are included in the New Hebrides-Fiji orogen because of evidence that they may be deforming rapidly. Surrounding plates are Australia (AU), Tonga (TO), Niuafo’ou (NI), and Pacific (PA). Conventions as in Figure 2, except coastlines are blue. Oblique Mercator projection on great circle passing E-W through (17°S, 174°E).
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.
Focal mechanism from GeoNet regional moment tensor solution with oblique-normal faulting at a depth of 112 km, and stations used to calculate the solution. pic.twitter.com/HksVtcddvF — John Ristau 🇨🇦 🇳🇿 (@SinistralSeismo) September 10, 2018 Displacement waveforms for a few New Zealand stations and Raoul Is (RIZ) from the 10/09/2018 Mw 7.0 Kermadec earthquake, ~750 km north of NZ. We felt this in Upper Hutt as a noticeable wobble, about 40 km north of WEL. pic.twitter.com/12IRY1TDlr — John Ristau 🇨🇦 🇳🇿 (@SinistralSeismo) September 10, 2018 Mw=7.0, SOUTH OF KERMADEC ISLANDS (Depth: 111 km), 2018/09/10 04:18:59 UTC – Full details here: https://t.co/Qw2GzqwyUl pic.twitter.com/r9KE8Ye78e — Earthquakes (@geoscope_ipgp) September 10, 2018
Return to the Earthquake Reports page. 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]. 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. The okhotsk plate is considered part of the North America plate on some maps. The location of the plate boundary of the Okhotsk plate are not well understood (e.g. using GPS plate motion velocities, it is difficult to find the northern boundary with the North America plate). Many of the earthquakes in this region are related to the subduction zone. Most notably is the 2011 Tohoku-oki M 9.1 tsunamigenic earthquake. More background information about the 2011 earthquake can be found here and information about the tsunami can be found here. The 2011 earthquake had lots of aftershocks and was quite complicated. One interesting thing that happened is that there was an extensional earthquake in the Pacific plate to the west of the Japan Trench. This M 7.7 earthquake happened along faults formed as the Pacific plate bends near where it meets the trench. Similar subduction zone / outer rise earthquake pairs are known, including some along the New Hebrides Trench in the western equatorial Pacific ocean, as well as further north along the Kuril subduction zone. I spend time discussing the 2006/2007 Kuril earthquake pair in this report. There was also a subduction zone earthquake in 2003, the Tokachi-oki earthquake, that triggered submarine landslides. These landslides transformed into turbidity currents and these were directly observed with offshore instrumentation. 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. I present more about the basics behind ground shaking, triggered landslides, and possible earthquake triggering on Temblor here: 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.
Maps showing tectonic context around the Japanese Islands (a) and geologic belts in Hokkaido (b; after Kato et al., 1990).
Geologic map around the Umaoi anticline redrawn from Geological Survey of Japan (2002). Location of active fault and/or fold scarps (after Ikeda et al., 2002) are also shown. buQ and bdQ attached on fault traces are upthrown and downthrown sides of faults, respectively. Sampling points of surface paleomagnetic data is after Kodama et al. (1993).
Geological map of Central Hokkaido with our seismic refraction/wide-angle reflection profiles and shot points (stars). Seismic reflection lines of the Hokkaido Transect were laid out from shot L-2 to M-5 on the wide-angle line. Reflection lines carried out from 1994 to 1997 in the southernmost part of the HCZ and refraction/wide-angle reflection lines in 1984 and 1992 are also shown. SYB: Sorachi-Yezo Belt; KMB: Kamuikotan Metamorphic Belt; IB: Idon’nappu Belt; HMB: Hidaka Metamorphic Belt; HB: Hidaka Belt; YB: Yubetsu Belt; TB: Tokoro Belt; HMT: Hidaka Main Trust.
Geological interpretation of the seismic model. KMB: Kamuikotan Metamorphic Belt; IB: Idon’nappu Belt; HMB: Hidaka Metamorphic Belt; Yz: Yezo Super Group; Sr: Sorachi Group; HMT: Hidaka Main Thrust.
Tectonic settings of the study region (black box). The solid sawtooth lines and the black dashed line denote the plate boundaries (Bird 2003). The red triangles denote the active volcanoes. The blue dashed lines and the pink lines denote the depth contours to the upper boundary of the subducting Pacific slab and that of the subducting Philippine Sea slab, respectively (Hasegawa et al. 2009; Zhao et al. 2012). The topography data are derived from the GEBCO_08 Grid, version 20100927, http://www.gebco.net. The ages of oceanic plates are from M¨uller et al. (2008).
(c) Distribution of the 4803 earthquakes used in
Tectonic setting of Kyushu within the Japanese island arc. The locations of active faults and volcanoes that have been active in the last 10,000 years are also shown.
Area affected by landslides in earthquakes of different magnitudes. Numbers beside data points are earthquakes listed in Table 1. Dots = onshore earthquakes; x = offshore earthquakes. Horizontal bars indicate range in reported magnitudes. Solid line is approximate upper bound enclosing all data.
Location and 12May 2008Wenchuan earthquake fault surface rupturemap, and focalmechanisms of the main earthquake (12May) and two of the major aftershocks (13 May and 25 May). Also the epicenters of historic earthquakes are indicated. The following faults are indicated: WMF: Wenchuan–Maowen fault; BF: Beichuan–Yingxiu fault; PF: Pengguan fault; JGF: Jiangyou–Guanxian fault; QCF: Qingchuan fault; HYF: Huya fault;MJF:Minjian fault based on the following sources: (Surface rupture: Xu et al., 2009a,b; Epicenter and aftershocks: USGS 2008; Historic earthquakes: Kirby et al., 2000; Li et al., 2008; Xu et al., 2009a,b).
Distribution of landslide dams triggered by the Wenchuan earthquake, China. The high landslide density zone is defined by a landslide area density >0.1 km−2; also shown are epicenters of historical earthquakes (USGS, 2008) and the historical Diexi landslide dams (Dahaizi, Xiaohaizi and Diexi). White polygons are unmapped due to the presence of clouds and shadows in post-earthquake imagery. WMF: Wenchuan–Maowen fault; YBF: Yingxiu–Beichuan fault; PF: Pengguan fault; JGF: Jiangyou–Guanxian fault; QCF: Qingchuan fault; HYF: Huya fault; MJF: Minjiang fault (after X. Xu et al., 2009). MJR: Minjiang River; MYR: Mianyuan River; JJR: Jianjiang River; QR: Qingjiang River.
Comparison of densities of blocking and non-blocking landslides. (a) Landslide density. (b) Landslide dam point density. White dashed lines are 240-km by 25-km swath profiles. (c). Mean normalized landslide and landslide dam densities along the SW–NE profile. Red lines are Yingxiu-Beichuan fault (YBF) and Pengguan fault (PF). Yellow dash lines are the boundary of the P1–P7 watersheds in the Pengguan Massif. YX, WC, HW, BC, and QC are the cities of Yingxiu, Wenchuan, Hanwang, Beichuan and Qingchuan, respectively. MJR, JJR, FJR, and QR represent Minjiang, Jianjiang, Fujiang and Qingjiang rivers, respectively.
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.
If you need information in English, you can call to Hokkaido Disaster Prevention Information (available 24 hours). Please refer to the link.#Japanearthquake#HokkaidoEarthquake Emergency information for foreigners – News – NHK WORLD – English https://t.co/5mXIWbuYzU — へニキ藤山 (@He2ki) September 6, 2018 Nice example of basin effects around Tokyo! https://t.co/r2UHEixJgK — Emily Wolin (@GeoGinger) September 6, 2018 Japan has more measurable #earthquakes than any other country and has over 100 active volcanoes. These both result from Japan being wedged among four major tectonic plates. Learn more – https://t.co/KGI16OduAI #JapanEarthquake pic.twitter.com/ADbi2T8kGv — IRIS Earthquake Sci (@IRIS_EPO) September 5, 2018 Landslides that seemed be happened by the 6th Sept 2018 M6.7 Hokkaido earthquake pic.twitter.com/eZAiculsHX — Deepa Mele Veedu (@deepameleveedu) September 6, 2018 今、NHKでも中継見てるけど、信じられない光景……。https://t.co/6aOXDKqWtq pic.twitter.com/drZBljla0a — よんます (@yonmas) September 6, 2018 NHK News stream – massive landslides, probably assisted by heavy rain in the previous 30 hours. Some houses were in the wrong place. Hopefully there wasn't anybody home, but at 3:08 am there probably was #Earthquake @LastQuake @TTremblingEarth @Ambassador_SR pic.twitter.com/p5fLJyNEfN — Jamie Gurney (@UKEQ_Bulletin) September 5, 2018 #Sapporo #Hokkaido Massive landslide due M6.6 earthquake @davepetley pic.twitter.com/pOsnQAPVaK — Luis Donoso (@Geo_Risk) September 6, 2018 釧路が停電し、街の明かりが消えていく様子#北海道地震 pic.twitter.com/ySa8Rg1kei — saimon98 (@saimon98se) September 5, 2018 It took 11min 18sec for the first seismic waves from today's M6.6 quake in Japan to reach my @raspishake in Turlock, CA. Picking up quakes from 4,860mi away… NBD. pic.twitter.com/g5y5fsD0Qk — Ryan Hollister (@phaneritic) September 6, 2018 Aerial video shows a landslide burying homes in Hokkaido after a strong magnitude 6.6 earthquake struck the northern Japan island 🎥: @nhk_news pic.twitter.com/pEXYLxnQ5m — BuzzFeed Storm (@BuzzFeedStorm) September 5, 2018 Mw=6.6, HOKKAIDO, JAPAN REGION (Depth: 30 km), 2018/09/05 18:07:58 UTC – Full details here: https://t.co/IS1AVC6Enn pic.twitter.com/WngxJgHQkp — Earthquakes (@geoscope_ipgp) September 5, 2018 This shows bedded marine sediments (turbidites) on plane with sliding. Likely explains it. pic.twitter.com/Ayr9Fp9VDy — Patrick Williams (@quake_science) September 6, 2018 Hundreds of landslides reported after 6.6 magnitude Japan quakehttps://t.co/MvqYg5kEez — Carlo Meletti (@CarloMeletti) September 5, 2018 After A strong 6.6 #earthquake #Terremoto #Temblor a Lightning #storm over Hokkaido #Japón #Japan right now ⚡ pic.twitter.com/nGqf8TKb5o — Teacher From PR 🌧️🌀🌩️ (@MaestroDEPR) September 5, 2018 今朝未明の北海道の地震は、当初は最大震度6強と見られましたが、最大震度7に修正されています。 — ウェザーニュース (@wni_jp) September 6, 2018 Helicopter rescues for those who authorities can reach – now the challenge is getting to those trapped inside the mud (currently nearly 20 missing). Currently 100 injured from the #japanearthquake in Hokkaido. Pics via NHK pic.twitter.com/Sp3bC49H4B — Jake Sturmer (@JakeSturmer) September 6, 2018 3 million without power, all flights to New Chitose Airport cancelled today as 6.7 quake hits Hokkaido (Shindo 6+ in some parts) #Japanearthquake pic.twitter.com/w5SssxpyEd — Jake Sturmer (@JakeSturmer) September 5, 2018 Bullet trains suspended too from the #Japanearthquake pic.twitter.com/dbfdTosIvM — Jake Sturmer (@JakeSturmer) September 5, 2018 Tomari nuclear plant using emergency generators – News – NHK WORLD – English https://t.co/GT1FJ4bIvP — patton_cascadia (@patton_cascadia) September 6, 2018 Near the epicenter, landslides wiped out homes in Atsuma. All of the missing are from this town.Helicopter crews are carrying out rescue operations. pic.twitter.com/MLubmtDTO4 — NHK WORLD News (@NHKWORLD_News) September 6, 2018 震度７を観測した北海道厚真町 NHKがドローンで撮影した映像です — NHKニュース (@nhk_news) September 6, 2018 More details are emerging about the landslides triggered by 6th September 2018 Hokkaido earthquake. The high landslide density may reflect recent rainfall from typhoon Jebi:- https://t.co/tbg1zba6Za pic.twitter.com/wYWid5PZDg — Dave Petley (@davepetley) September 6, 2018 Pre- and post-seismic image of 2018 Hokkaido earthquake. Phenomenal landslides. — Jay Tung (@jaytung_earth) September 6, 2018 ALOS-2 InSAR interferogram of #HokkaidoEarthquake . — Sadra Karimzadeh (@Sadra_Krmz) September 6, 2018 Liquefaction probability map after #HokkaidoEarthquake M 6.6 https://t.co/Or2K7xnZIB pic.twitter.com/Qz5uVGYL0m — Sadra Karimzadeh (@Sadra_Krmz) September 6, 2018 — temblor (@temblor) September 7, 2018 Actualización terremoto #Hoakkaido, Japón🇯🇵. Asciende a 20 cifra de decesos; aún reportan personas desaparecidas. Se observa licuefacción: suelos saturados de agua, que suben a superficie, pierden firmeza por la sacudida del sismo desestabilizando el suelo. Créditos: NHK pic.twitter.com/zHOr1HR1tx — SkyAlert (@SkyAlertMx) September 7, 2018 Death toll rises to 30 in the aftermath of Japan's Hokkaido earthquakehttps://t.co/z9b8LdSvhZ — TIME (@TIME) September 8, 2018 NASA JPL-Caltech ARIA preliminary deformation map from Copernicus Sentinel-1 data for 5 September 2018 Hokkaido earthquake. Total motion is approximate due to very high noise level (low coherence), but deformation signal is between 9 and 14 cm of motion up and east. pic.twitter.com/YoL2IvdjSO — Eric Fielding (@EricFielding) September 9, 2018 Comparison view between 2015 (up) and post-earthquake (below) reveals the extent of co-seismic #landslides from the M6.6 #earthquake near Atsuma, Hokkaido, #Japan. Point cloud data for 2015 & 2018 extracted from aerial imagery provided by Japan Geographical Survey Institute. pic.twitter.com/lriXZt10Za — Sotiris Valkaniotis (@SotisValkan) September 10, 2018 Slippery volcanic soils blamed for deadly landslides during #Hokkaido earthquake, reports @guardianeco https://t.co/BhB0sm8kHW pic.twitter.com/sX8BFAXZfJ — EGU (@EuroGeosciences) September 11, 2018 【地殻変動情報】だいち2号のSARデータを使用した解析による、 #平成30年北海道胆振東部地震 に伴う地殻変動分布図を公開しました。 — 国土地理院 (@GSI_chiriin) September 10, 2018 High quality drone footage has been posted on Facebook providing detailed views of the landslides from the 2018 Hokkaido Eastern Iburi earthquake:- https://t.co/pjMXJOAxkK pic.twitter.com/LZJ1zUzwk2 — Dave Petley (@davepetley) September 11, 2018 Potential liquefaction damage map in urban areas based on LiquickMap, slope map, differential InSAR coherence and weighted overlay analysis (WOA). #hokkaidoearthquake pic.twitter.com/rJejYS2D8Y — Sadra Karimzadeh (@Sadra_Krmz) September 12, 2018 GNSS and ALOS-2 InSAR observations, and fault model for Mj6.7 #HokkaidoEarthquake on Sep 6 by GSI. The depth of the upper edge of the fault is ~15km, much shallower than the hypocenter depth (>30km). https://t.co/iQBE4GwPtL pic.twitter.com/0MX9PhWG5h — Yu Morishita (@Yu__Morishita) September 12, 2018 Slippery volcanic soils blamed for deadly landslides during Hokkaido earthquake https://t.co/s3WAAygPOr — temblor (@temblor) September 16, 2018
Return to the Earthquake Reports page.
Earthquake Report: Iran
The M 7.3 earthquake was a reverse/thrust earthquake associated with tectonics of the Zagros fold and thrust belt. This plate boundary fault system is a section of the Alpide belt, a convergent plate boundary that extends from the west of the Straits of Gibraltar, through Europe (causing uplift of the Alps and subduction offshore of Greece), the Middle East, India (causing the uplift forming the Himalayas), then to end in eastern Indonesia (forming the continental collision zone between Australia and Indonesia).
Some of the earthquakes (including this one) are strike-slip earthquakes (see explanation of different earthquake types below in the geologic fundamentals section). So, one might ask why there are strike-slip earthquakes associated with a compressional earthquake?
As pointed out by Baptiste Gombert, these strike-slip earthquakes are are evidence of strain partitioning. Basically, when relative plate motion (the direction that plates are moving relative to each other) is not perpendicular or parallel to a tectonic fault, this oblique motion is partitioned into these perpendicular and parallel directions.
A great example of this type of strain partitioning is the plate boundary offshore of Sumatra where the India-Australia plate subducts beneath the Sunda plate (part of Eurasia). The plate boundary is roughly N45W (oriented to the northwest with an azimuth of 325°) and the relative plate motion direction is oriented closer to a north-south orientation. The relative plate motion perpendicular to the plate boundary is accommodated by earthquakes on the subduction. These earthquakes are oriented showing compression in a northeast direction. Along the axis of Sumatra is a huge strike-slip fault called the Great Sumatra fault. This fault is parallel to the plate boundary and accommodates relative plate motion parallel to the plate boundary. The Great Sumatra fault is a fault called a forearc sliver fault.
There are other examples of this elsewhere, like here in western Iran/eastern Iraq. Relative plate motion between the Arabia and Eurasia plates is oriented north-south, but the plate boundary is oriented northwest-southeast (just like the Sumatra example). So this oblique relative plate motion is partitioned into fault normal compression (the M 7.3 earthquake) and fault parallel shear (today’s M 6.3 earthquake).
There is also a strike-slip fault in the region of today’s M 6.3, the Khanaqin fault. So, given what we know about the tectonics and historic seismicity, I interpret today’s M 6.3 earthquake to have been a strike-slip earthquake associated with the Khanaqin fault, triggered by changes in stress by the M 7.3 earthquake. I could be incorrect and this earthquake could be unrelated to the > 7.3 earthquake.Below is my interpretive poster for this earthquake
I include an inset map showing seismicity from 2016.11.22 through 2018.11.28 showing the aftershocks from the M 7.3 earthquake. Note the cluster of earthquakes to the south of the aftershock zone. This is a swarm with earthquakes in the lower to mid M 5 range. The earthquakes with mechanisms are compressional, oriented the same as the M 7.3.
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 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
Geologic Fundamentals
Compressional:
Extensional:
Middle East
General Overview
Earthquake Reports
Social Media
UPDATE: 2018.11.26
This website automatically display coseismic deformation maps of recent M >= 6 earthquakes for rapid hazard evaluations. pic.twitter.com/gDqRceAHK7
References:
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: Greece
Then, the M 6.8 mainshock hit while i was out and about, followed by a M = 5.2 aftershock.
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.
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.
There are records of tsunami observed on tide gage data.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.
The poster below includes earthquakes that represent the different plate boundaries and tectonic regimes.
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
proportional to the amount of movement. The thick black arrows indicate the mean motion vectors of the plates. The polygonal areas on the map (dashed lines) define the approximate borders of the five different structural regions discussed in the text. The borders between structural regions are not straightforward, and wide transitional zones probably exist between them. The inset shows a schematic map with the geodynamic framework in the eastern Mediterranean area (modified from McClusky et al., 2000). DSF—Dead Sea fault; EAF—East Anatolia fault; HT—Hellenic trench; KFZ— Kefallonia fault zone; MRAC—Mediterranean Ridge accretionary complex; NAF—North Anatolia fault; NAT—North Aegean trough.
Geologic Fundamentals
Compressional:
Extensional:
Europe
General Overview
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/Landslide/Tsunami Report: Donggala Earthquake, Central Sulawesi: UPDATE #1
M 7.5 Doggala Earthquake
My 2018.10.01 BC Newshour Interview
Optical Analysis
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.
Below are a series of different InSAR analytical results.
Tsunami
Tsunami can be caused by a variety of processes, including earthquakes, volcanic eruptions, landslides, and meteorological phenomena. Earthquakes, eruptions, and landslides cause tsunami when these processes displace water in some way. We may typically associate tsunami with subduction zone earthquakes because these earthquakes are the type that generate vertical land motion along the sea floor. However, we know that strike-slip earthquakes can also generate tsunami (e.g. the 1999 Izmit, Turkey earthquake). But strike-slip earthquakes typically generate tsunami that are smaller in size.
When landslides generate tsunami, they are often localized relative to the location of the landslide. The tsunami size can be rather large near the landslide and the size diminishes rapidly with distance from the landslide. An example of a landslide generated tsunami is the 1998 Papua New Guinea tsunami (an earthquake triggered a landslide, causing a “larger than expected” tsunami to inundate the land there. The size of the tsunami was very large near the landslide.
Based on post-earthquake satellite imagery from Digital Globe, the overwhelming majority of tsunami damage is localized within Palu Bay. The severity of damage is worse in southern Palu Bay where tsunami inundation is on the order of 300 feet. While at the northern part of the bay, inundation is on the order of 50 feet. In the north, most of the buildings that were destroyed by the tsunami were built over the water, though not entirely. While in the south, building damage extends further inland where buildings have been destroyed that were not built over the water. North of the mouth of the bay, there is less evidence for tsunami inundation, but there is localized damage in places.
There was a tsunami recorded at the Pantoloan Port tide gage with an amplitude of about 1 meter. At this location is also a 50 long ship that was lifted up onto a dock at the port. More details about the observations made by the joint Indonesia/Japan post-tsunami survey team cab be found at Temblor here.
M 7.5 Landslide Model vs. Observation Comparison
References:
Earthquake Report: New Britain!
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.
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.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
Here is a visualization of the seismicity as presented by Dr. Steve Hicks.
Geologic Fundamentals
Compressional:
Extensional:
New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports
Earthquake Reports
Social Media
References:
Earthquake Report: Sulawesi (Celebes), Indonesia
UPDATE 2018.09.28 23:00
UPDATE 2018.09.29 07:00
UPDATE 2018.09.29 10:45
UPDATE 2018.09.30 17:00
Below is my interpretive poster for this earthquake
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
Geologic Fundamentals
Compressional:
Extensional:
Indonesia | Sumatra
General Overview
Earthquake Reports
Philippines | Western Pacific
Earthquake Reports
Social Media
After 7.7 SR earthquake strike Palu, then tsunami hit this city. #EarthQuake #Gempa #Tsunami #Palu #PrayForIndonesia #PrayForPalu #PrayForDonggala pic.twitter.com/G3JxTaUZx9
Earthquake just off Sulawesi island, #Indonesia. Triggering a powerful tsunami. Video captured by a local. #tsunami #breakingnews #Televisa Video del momento en el que llego el #Tsunamipic.twitter.com/bZgBUh2bGa
UPDATE 2018.09.29 07:00
References:
Earthquake Report Pages
Earthquake Report: Kermadec
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
shown in the inset figure, with the gray dotted box indicating the expanded region in the main figure.
Geologic Fundamentals
Compressional:
Extensional:
New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports
Earthquake Reports
Social Media
References:
°
≥
ñEarthquake Report: Hokkaido, Japan
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 active crustal faults from the Coordinating Committee for Geoscience Programmes in East and Southeast Asia (CCOP). Note the abundance of north-northwest oriented yellow lines to the east of today’s earthquakes. While today’s earthquake was not on those crustal faults, the earthquakes and these faults are responding to similarly oriented tectonic stresses.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Some Relevant Discussion and Figures
this study. The black crosses denote 3818 events (Group-1) that occurred under the seismic network. The green dots show 228 events (Group-2) that occurred outside the seismic network, selected from the events relocated by Gamage et al. (2009) using sP depth phases. The red dots denote 757 suboceanic earthquakes (Group-3) that are newly relocated in this work using P-wave, S-wave and sP depth-phase data. (d) East–west and (e) north–south vertical cross-sections of the earthquakes shown in (c).
Earthquake Triggered Landslides
Geologic Fundamentals
Compressional:
Extensional:
Japan | Izu-Bonin | Mariana
Earthquake Reports
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震度7を観測した厚真町では土砂崩れが相次ぎ、新千歳空港は閉鎖、札幌市内で液状化現象、全道で停電など広範囲で影響が出ています。
今後も大きな余震に警戒が必要です。https://t.co/Tfi8PeI3gr pic.twitter.com/ZeVKpjduA5
#nhk_news #ドローン #地震 #震度７ #厚真町
#土砂崩れ pic.twitter.com/jaSVW78yupUPDATE 2018.09.06
Credit: https://t.co/Cu6UjVmIpQ pic.twitter.com/sZd7E4MTDT
Source: https://t.co/7K2hfGwqM0
master and slave: 2018/08/23 & 2018/09/06 pic.twitter.com/zuLUM8nlbs
UPDATE 2018.09.07
UPDATE 2018.09.08
UPDATE 2018.09.09
UPDATE 2018.09.10
UPDATE 2018.09.11
今後も地殻変動の監視を続けていきます。
詳細はこちら→https://t.co/vDFA0hYtOd pic.twitter.com/ivFreV1bFL
UPDATE 2018.09.12
UPDATE 2018.09.16
References:
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