Early this morning I received some notifications of earthquakes along the Tonga trench (southwestern central Pacific Ocean). It was about 2am my local time.
I work on the tsunami program for the California state tsunami program (CTP) and we respond to tsunami to (1) help local communities do their first response activities so that they can help reduce suffering and to (2) document the impact of these tsunami.
Because of this work, our team is “at the ready” 24 hours a day, 7 days a week, to respond to these events. Luckily, this event was unlikely to generate a tsunami that would impact California. I went back to sleep.
This morning I put together a report and checked to see if there was a tsunami generated. Here is one place that I check for tsunami records as observed on tide gages http://www.ioc-sealevelmonitoring.org/map.php. I did not see anything convincing.
This earthquake, from last night my time, has a magnitude of M 7.3.
https://earthquake.usgs.gov/earthquakes/eventpage/us7000ip0l/executive
This area of the Earth has a plate boundary fault system called a subduction zone. A subduction zone is a convergent plate boundary, which means that the plates on either side of the boundary move towards each other.
Here, the Pacific plate dives westwards beneath the Australia plate, forming the Tonga trench. Below is a schematic illustration showing what these plates may look like if we cut into the Earth and viewed this subduction zone from the side. Note the Pacific plate on the right and the Australia plate on the left, with the megathrust subduction zone fault where they meet.
This illustration shows where earthquakes may happen along this plate boundary. There could be interface earthquakes along the megathrust fault (megathrust earthquakes). These are what most people are familiar with when they are thinking about tsunami (e.g., the 2011 Great East Japan Earthquake and Tsunami).
In the upper plate (the Australia plate), there can be crustal fault earthquakes. In the lower plate (the Pacific plate) there can be slab earthquakes (events within the crust, aka the slab), and there can be outer rise earthquakes).
The outer rise is a part of the plate that is warping up and down because of the forces adjacent to the subduction zone. This warping can cause extension in the upper part, and compression in the lower part, of this plate.
This 11 Nov 2022 M 7.3 earthquake was a compressional (reverse) earthquake in the outer rise region of this plate boundary. It was pretty deep (for oceanic crust) so fits nicely in the correct place in this illustration:
But megathrust earthquakes are not the only type of earthquake that can cause a tsunami. The 2009 magnitude M 8.1 extensional (normal) fault earthquake near Samoa and American Samoa caused a tsunami that inundated the nearby islands (causing lots of damage and human suffering). This tsunami also travelled across the Pacific Ocean to impact California! (This is why the California Tsunami Program monitors tsunami across the Pacific Basin, so that we can help reduce suffering through the evacuation of coastal areas. Remember, the entire coast of California is a Tsunami Hazard Area.)
Below is my interpretive poster for this earthquake
- I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1922-2022 with magnitudes M ≥ 7.0 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.
- A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
- Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.
- In the upper left corner is a map that shows the plates, their boundaries, and a century of seismicity.
- In the lower right corner is a map that shows the ground shaking from the earthquake, with color representing intensity using the Modified Mercalli Intensity (MMI) scale. The closer to the earthquake, the stronger the ground shaking. The colors on the map represent the USGS model of ground shaking. The colored circles represent reports from people who posted information on the USGS Did You Feel It? part of the website for this earthquake. There are things that affect the strength of ground shaking other than distance, which is why the reported intensities are different from the modeled intensities.
- To the left is a plot that shows how the shaking intensity models and reports relate to each other. The horizontal axis is distance from the earthquake and the vertical axis is shaking intensity (using the MMI scale, just like in the map to the right: these are the same datasets).
- Further to the left is a diagram that shows the different types of earthquakes that can occur along a subduction zone.
- In the upper right corner is a map that shows some of the historic earthquakes in the region, with the earthquake mechanisms. I labeled these events for the type of event that I interpret them to be.
- In the upper left center is a map from Richards et al. (2011) that shows earthquake locations (epicenters) with color representing depth. I place a yellow star in the general location of today’s M 7.3 earthquake. These colors help us visualize how the Pacific plate dips deeper towards the left (yellow are shallow events and purple are deep events). The 2000.01.08 M 7.2 earthquake is an intermediate depth earthquake (see the map in the upper right corner).
- In the right center is a map from Timm et al (2013) that also shows the depth to the slab (the downgoing Pacific plate). I place a yellow star in the general location of today’s M 7.3 earthquake.
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
- Well, I just looked at Pago Pago and the record is clear. I am kinda surprised since this gage is on the nodal plane for this event. I will plot these data up.
- Here is a screenshot:
- Here are the two plots for the gages listed above. The Pago pago record is quite clear. However, the Nukualofa gage is pretty noisy. I don’t have much confidence in the measurements of the wave size.
- Data from both gages show a background wave sequence that makes it difficult to know when the tsunami ends. Someone who can filter out that wave series could probably do a better job at locating when the tsunami ends, at least for the Pago Pago data.
- Pago Pago (American Samoa) https://webcritech.jrc.ec.europa.eu/SeaLevelsDb/Device/959
- Nukualofa (Tonga Island) https://webcritech.jrc.ec.europa.eu/SeaLevelsDb/Device/950
Other Report Pages
Some Relevant Discussion and Figures
- Here is the map from Timm et al., 2013.
Bathymetric map of the Tonga–Kermadec arc system. Map showing the depth of the subducted slab beneath the Tonga–Kermadec arc system. Louisville seamount ages are after Koppers et al.49 ELSC, eastern Lau-spreading centre; DSDP, Deep Sea Drilling Programme; NHT, Northern Havre Trough; OT, Osbourn Trough; VFR, Valu Fa Ridge. Arrows mark total convergence rates.
- Here is the oblique view of the slab from Green (2003).
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. 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 olivine
- Here are figures from Richards et al. (2011) with their figure captions below in blockquote.
- The main tectonic map
- Here is the map showing the current configuration of the slabs in the region.
- This is the cross section showing the megathrust fault configuration based on seismic tomography and seismicity.
- Here is their time step interpretation of the slabs that resulted in the second figure above.
bathymetry, and major tectonic element map of the study area. The Tonga and Vanuatu subduction systems are shown together with the locations of earthquake epicenters discussed herein. Earthquakes between 0 and 70 km depth have been removed for clarity. Remaining earthquakes are color-coded according to depth. Earthquakes located at 500–650 km depth beneath the North Fiji Basin are also shown. Plate motions for Vanuatu are from the U.S. Geological Survey, and for Tonga from Beavan et al. (2002) (see text for details). Dashed line indicates location of cross section shown in Figure 3. NFB—North Fiji Basin; HFZ—Hunter Fracture Zone.
Map showing distribution of slab segments beneath the Tonga-Vanuatu region. West-dipping Pacifi c slab is shown in gray; northeast-dipping Australian slab is shown in red. Three detached segments of Australian slab lie below the North Fiji Basin (NFB). HFZ—Hunter Fracture Zone. Contour interval is 100 km. Detached segments of Australian plate form sub-horizontal sheets located at ~600 km depth. White dashed line shows outline of the subducted slab fragments when reconstructed from 660 km depth to the surface. When all subducted components are brought to the surface, the geometry closely approximates that of the North Fiji Basin.
Previous interpretation of combined P-wave tomography and seismicity from van der Hilst (1995). Earthquake hypocenters are shown in blue. The previous interpretation of slab structure is contained within the black dashed lines. Solid red lines mark the surface of the Pacifi c slab (1), the still attached subducting Australian slab (2a), and the detached segment of the Australian plate (2b). UM—upper mantle;
TZ—transition zone; LM—lower mantle.
Simplified plate tectonic reconstruction showing the progressive geometric evolution of the Vanuatu and Tonga subduction systems in plan view and in cross section. Initiation of the Vanuatu subduction system begins by 10 Ma. Initial detachment of the basal part of the Australian slab begins at ca. 5–4 Ma and then sinking and collision between the detached segment and the Pacifi c slab occur by 3–4 Ma. Initial opening of the Lau backarc also occurred at this time. Between 3 Ma and the present, both slabs have been sinking progressively to their current position. VT—Vitiaz trench; dER—d’Entrecasteaux Ridge.
- Here is the tectonic map from Ballance et al., 1999.
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).
- Here is a great summary of the fault mechanisms for earthquakes along this plate boundary (Yu, 2013).
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
shown in the inset figure, with the gray dotted box indicating the expanded region in the main figure.
- 2022.11.11 M 7.3 Tonga
- 2022.09.10 M 7.6 Papua New Guinea
- 2021.03.04 M 8.1 Kermadec
- 2021.02.10 M 7.7 Loyalty Islands
- 2019.06.15 M 7.2 Kermadec
- 2019.05.14 M 7.5 New Ireland
- 2019.05.06 M 7.2 Papua New Guinea
- 2018.12.05 M 7.5 New Caledonia
- 2018.10.10 M 7.0 New Britain, PNG
- 2018.09.09 M 6.9 Kermadec
- 2018.08.29 M 7.1 Loyalty Islands
- 2018.08.18 M 8.2 Fiji
- 2018.03.26 M 6.9 New Britain
- 2018.03.26 M 6.6 New Britain
- 2018.03.08 M 6.8 New Ireland
- 2018.02.25 M 7.5 Papua New Guinea
- 2018.02.26 M 7.5 Papua New Guinea Update #1
- 2017.11.19 M 7.0 Loyalty Islands Update #1
- 2017.11.07 M 6.5 Papua New Guinea
- 2017.11.04 M 6.8 Tonga
- 2017.10.31 M 6.8 Loyalty Islands
- 2017.08.27 M 6.4 N. Bismarck plate
- 2017.05.09 M 6.8 Vanuatu
- 2017.03.19 M 6.0 Solomon Islands
- 2017.03.05 M 6.5 New Britain
- 2017.01.22 M 7.9 Bougainville
- 2017.01.03 M 6.9 Fiji
- 2016.12.17 M 7.9 Bougainville
- 2016.12.08 M 7.8 Solomons
- 2016.10.17 M 6.9 New Britain
- 2016.10.15 M 6.4 South Bismarck Sea
- 2016.09.14 M 6.0 Solomon Islands
- 2016.08.31 M 6.7 New Britain
- 2016.08.12 M 7.2 New Hebrides Update #2
- 2016.08.12 M 7.2 New Hebrides Update #1
- 2016.08.12 M 7.2 New Hebrides
- 2016.04.06 M 6.9 Vanuatu Update #1
- 2016.04.03 M 6.9 Vanuatu
- 2015.03.30 M 7.5 New Britain (Update #5)
- 2015.03.30 M 7.5 New Britain (Update #4)
- 2015.03.29 M 7.5 New Britain (Update #3)
- 2015.03.29 M 7.5 New Britain (Update #2)
- 2015.03.29 M 7.5 New Britain (Update #1)
- 2015.03.29 M 7.5 New Britain
- 2015.11.18 M 6.8 Solomon Islands
- 2015.05.24 M 6.8, 6.8, 6.9 Santa Cruz Islands
- 2015.05.05 M 7.5 New Britain
New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports
General Overview
Earthquake Reports
Social Media
#EarthquakeReport for M 7.3 #Earthquake along outer rise near the Tonga trench
reverse (compressional) mechanism
south of analogues incl tsunamigenic 2009 M 8.1 (tho that was extensional)https://t.co/gQEdISt9eD
learn more abt regional tectonics herehttps://t.co/eDsUON2Mly pic.twitter.com/DvMnY4rWck
— Jason "Jay" R. Patton (@patton_cascadia) November 11, 2022
#EarthquakeReport for M 7.3 #Earthquake near the Tonga trench
thrust (compressional) earthquake along the outer rise
no #Tsunami observed on tide gages
report here includes my interpretation and a regional tectonic summary:https://t.co/ze2s3bb7Vn pic.twitter.com/2M3SZaYE19
— Jason "Jay" R. Patton (@patton_cascadia) November 11, 2022
The region near todays M7.3 earthquake is incrediblely active due to the high rates of convergence between the Australian and Pacific Plates. Since 1900, 40 M7.5+ earthquakes have been recorded, as well as at least 3 M8+ events. https://t.co/avVOX0LcGH pic.twitter.com/dN9mIrwgwN
— Wendy Bohon, PhD 🌏 (@DrWendyRocks) November 11, 2022
Fri Nov 11 10:48:00 2022 UTC
Mag: 7.5 Depth: 33
Coords: 19.322 S 172.01 W
Location: TONGA ISLANDS REGION* HAZARDOUS TSUNAMI WAVES FROM THIS EARTHQUAKE ARE POSSIBLE WITHIN 300 KM OF THE EPICENTER ALONG THE COASTS OF
NIUE AND TONGA pic.twitter.com/lm1RMEJ0o8— よっしみ~☆🌏 (@yoshimy_s) November 11, 2022
Seismic waves from the Tonga 7.3 #earthquake, as arriving at a @raspishakEQ station of the @GEO3BCN_CSIC educational network in NE Iberia pic.twitter.com/K6YZPQf1JU
— Jordi Diaz Cusi (@JDiazCusi) November 11, 2022
Recent Earthquake Teachable Moment for the M7.3 Tonga earthquake https://t.co/PJBT5jgOTy pic.twitter.com/h0kTCejygS
— IRIS Earthquake Sci (@IRIS_EPO) November 11, 2022
Global surface and body wave sections from the M7.3 earthquake near Tongahttps://t.co/mz6A6vgD9F pic.twitter.com/0psyiRcDum
— IRIS Earthquake Sci (@IRIS_EPO) November 11, 2022
Mw=7.3, TONGA ISLANDS REGION (Depth: 43 km), 2022/11/11 10:48:42 UTC – Full details here: https://t.co/vqxit49tby pic.twitter.com/m16qoCB5wK
— Earthquakes (@geoscope_ipgp) November 11, 2022
Watch the waves from the M7.3 earthquake near Tonga roll across seismic stations in North America (THREAD 🧵) pic.twitter.com/hupVx0WfpQ
— IRIS Earthquake Sci (@IRIS_EPO) November 11, 2022
Section from today's M7.3 earthquake in the Tonga region at 2022-11-11 10:48:45UTC recorded on the worldwide @raspishake network. See: https://t.co/LS1S4JlAqX. Uses @obspy and @matplotlib. pic.twitter.com/Jdz1FlEZN2
— Mark Vanstone (@wmvanstone) November 11, 2022
A cross-section of seismicity, with the focal mechanisms projected into the vertical plane, shows the three deep quakes with purple outlines. These events were close to the deepest quakes in this area, where the subducted slab possibly is deflected by the 670 km discontinuity. pic.twitter.com/V09EYGWJRd
— Jascha Polet (@CPPGeophysics) November 11, 2022
- 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>
- Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
- 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.
- 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
- Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
- Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
- Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198
- Richards, S., Holm, R., and Barber, G., 2011. Skip Nav Destination When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region in Geology, c. 39, no. 8, p. 787-790, https://doi.org/10.1130/G31937.1
- Timm, C., Bassett, D., Graham, I. et al. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga–Kermadec arc. Nat Commun 4, 1720 (2013). https://doi.org/10.1038/ncomms2702
References:
Basic & General References
Specific References
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There have not been that many large earthquakes this year. This is good for one main reason, there is a lower potential for human suffering. Therefore, there are fewer Earthquake Reports for this year. This morning (my time) there was a magnitude M 6.9 earthquake along the Romanche transform fault, a right-lateral strike-slip fault system that offsets the Mid Atlantic Ridge in the equatorial Atlantic Ocean. The fault is part of the Romanche fracture zone. https://earthquake.usgs.gov/earthquakes/eventpage/us7000i53f/executive The transform faults in this part of the Mid Atlantic Ridge plate boundary have a pattern of earthquakes that seem to max out in the lower 7 magnitudes. This may be (at least partly) due to the maximum length of these faults (?). The Romanche fault is about 900 kilometers long. The Chain fault is about 250 km long. The St. Paul fault is about 350 km long. Using empirical (data) based relations between earthquake subsurface rupture length and earthquake magnitude (Wells and Coppersmith, 1994), I calculate the maximum earthquake magnitude we may get on these three faults listed above. Here are the data that Wells and Coppersmith use to establish these relations.
(a) Regression of subsurface rupture length on magnitude (M). Regression line shown for all-slip-type relationship. Short dashed line indicates 95% confidence interval. (b) Regression lines for strike-slip relationships. See Table 2 for regression coefficients. Length of regression lines shows the range of data for each relationship.
Here are the magnitude estimates for each of these fault systems. Looking at the interpretive poster, we can see that there have not been any temblors that approach the sizes listed in this table. The largest historic earthquake was M 7.1 (there were several). So, we may ask ourselves one of the most common questions people ask regarding earthquakes. Was this M 6.9 a foreshock to a larger earthquake? Obviously, we cannot yet know this. Nobody can predict the future (at least not yet). However, based on the incredibly short historic record of earthquakes, we may answer this question: “no, probably not.” This answer is tempered by the very short seismic record. If magnitude 8 earthquakes occur, on average, every 1000 years, then our ~100 year record might be too short to “notice” one of these M 8 events. So, given the historic record, it sure seems likely that there may be another M6-7 earthquakes in the region of the fault sometime in the next couple of months. And, given our lack of knowledge about the long term behavior of these faults, it is also possible that there could be a larger M 8 event.
A: Multibeam topography of Romanche region, showing north-south profiles where sampling was carried out. Black dots and red numbers indicate estimated age (in million years) of lithosphere south of Romanche Transform, assuming spreading half-rate of 17 mm/yr within present-day ridge and transform geometry. White dots indicate epicenters of teleseismically recorded 1970–1995 events (magnitude . 4). FZ is fracture zone. B: Topography and petrology at eastern intersection of Romanche Fracture Zone with Mid-Atlantic Ridge. Data were obtained during expeditions S-16, S-19, and G-96 (Bonatti et al., 1994, 1996). C: Location of A along Mid-Atlantic Ridge.
Seismotectonic context. The map location is given by the red rectangle on the inset globe. Focal mechanisms are shown for events with Mw > 6 (ref. 30). Mw > 7.0 events are labelled. Stations of the PI-LAB ocean bottom seismometer network are indicated by triangles. Our relocated hypocentre and low-frequency RMT of the 2016 earthquake are shown by the red star and red beach ball, respectively. The orange beach ball is a colocated Mw 5.8 used for the Mach cone analysis. The black rectangle shows the location of the map in Fig. 2. ISC Bulletin, Bulletin of the International Seismological Centre.
Interpretation of rupture dynamics for the 2016 Romanche earthquake. Top: perspective view of bathymetry along the Romanche FZ. Bottom: interpretive cross-section along the ruptured fault plane. Colours show a thermal profile based on half-space cooling. The green line denotes the predicted transition between velocity-strengthening and velocity-weakening frictional regimes (as expressed by the a – b friction rate parameter) from Gabbro data35. The numbers show the key stages of rupture evolution: (1) rupture initiation (star) in the oceanic mantle, (2) initiation phase has sufficient fracture energy to propagate upwards to the locked section of fault, (3) weak subshear rupture front travels east in the lower crust and/or upper mantle, (4) rupture reaches the locked, thinner crustal segment close to the weaker RTI (SE1), (5) sufficient fracture energy for a westward supershear rupture in the crust along the strongly coupled fault segment (SE2) and (6) rupture possibly terminated by a serpentinized and hydrothermally altered fault segment.
#EarthquakeReport for M 6.9 #Earthquake along the equatorial Mid Atlantic Ridge plate boundary a right-lateral strike-slip earthquake along the Romanche transform faulthttps://t.co/LkglWJgBvD read the report herehttps://t.co/8ZGxTJEU9v pic.twitter.com/axcwlSPDSI — Jason "Jay" R. Patton (@patton_cascadia) September 5, 2022 Mw=7.0, CENTRAL MID-ATLANTIC RIDGE (Depth: 25 km), 2022/09/04 09:42:18 UTC – Full details here: https://t.co/MaNnp6eDAU pic.twitter.com/Gv39KoU3KQ — Earthquakes (@geoscope_ipgp) September 4, 2022 Magnitude 6.9 #earthquake on the mid-Atlantic ridge a couple of hours ago (2022-09-04Z09:42) https://t.co/GwKH4H1yON Predominantly strike-slip (as expected there). Amazing T-phases on the Ascension island hydrophones (data via @IRIS_EPO) coming after the weaker converted P-wave. pic.twitter.com/rCwawAet0W — Dr. Steven J. Gibbons (@stevenjgibbons) September 4, 2022 Major M6.9 right lateral fault #eartquake in oceanic Romanche fracture zone, offsetting central Mid-Atlantic Ridge (3cm/y). Large one for geologic setting, but no surface impact; no tsunami. Textbook behavior. #geohazards https://t.co/F3hXqtkikg pic.twitter.com/KcHL6p1nca — 🌎 Prof Ben van der Pluijm ⚒️ (@vdpluijm) September 4, 2022 Magnitude 6.9 earthquake on the Mid-Atlantic ridge, recorded in New England – detected in Maine, Massachusetts and the Westport Observatory's seismic equipment 4,340 miles from the epicenter in the middle of the Atlantic ocean. @Weston_Quakes https://t.co/dS9MJOU3ow pic.twitter.com/wUJwQ8XBqh — WestportAstroSociety (@westportskyguys) September 4, 2022 2022-09-04 strong M6.9 Central Mid-#Atlantic Ridge #earthquake recorded by online high quality data #RaspberryShakes + 3D trace from Canindé de São Francisco, #Brazil (2031.6km away) + area historical seismicity.#Python @raspishake @matplotlib #CitizenScienc pic.twitter.com/QYqq7lJPaW — Giuseppe Petricca (@gmrpetricca) September 4, 2022
In the middle of the night (my time) I got a notification from the EMSC earthquake notification service. I encourage everyone to download and use this app. There was an intermediate depth magnitude M 7.5 earthquake in Peru. The tectonics in this region of the world are dominated by the convergent plate boundary, a subduction zone formed by the convergence of the oceanic Nazca and continental South America plates. https://earthquake.usgs.gov/earthquakes/eventpage/us7000fxq2/executive As the Nazca plate subducts, it dips below the South America plate at different dip angles. In this region of Peru, the dip angle is shallow and we term this flat-slab subduction. This M 7.5 earthquake occurred in the downgoing Nazca plate, so was not a subduction zone megathrust event, but a “slab” event (for being in the Nazca slab). I prepared a much more extensive report for a M 8.0 earthquake in a nearby location that happened on 26 May 2019. Read more about the tectonics of this region in that report here. Was this M 7.5 an aftershock of the M 8.0? Probably not, based on the USGS M 8.0 slip model. However this M 7.5 could have been triggered by changes in static coulomb stress following the M 8.0. I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events. Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here. I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events. Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here. Last afternoon (my time) there was an M 7.0 earthquake near Acapulco, Mexico. This event generated a tsunami, landslides, building damage, casualties (one fatality as I write this), and many emotions. https://earthquake.usgs.gov/earthquakes/eventpage/us7000f93v/executive I present my interpretive poster and a few figures. Read more about the tectonics of this region here, in a report for an M 7.4 earthquake in 2020.
I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events. Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here. On 14 August ’21 there was a magnitude M 7.2 oblique strike-slip earthquake in Haiti. This earthquake was along the Enriquillo-Plantain Garden fault zone, which also ruptured in 2010. Here is my report for the 2010 Haiti earthquake (see more about the tectonics of this region of the world). https://earthquake.usgs.gov/earthquakes/eventpage/us6000f65h/executive 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. My original Tweet: #EarthquakeReport for M7.2 #TremblementDeTerre #Terrremoto #Earthquake in #Haiti #HaitiEarthquake #HaitiEarthquake2021 updated poster: compare shaking intensity MMI and aftershock regions between 2010 M 7.0 & 2021 M 7.2 read more about 2010 M 7 Event https://t.co/KDzf1PtjyE pic.twitter.com/wIURgKsbOa — Jason "Jay" R. Patton (@patton_cascadia) August 15, 2021 Haiti's 1860 Jour de Pâques earthquakes may have released strain in key fault zone https://t.co/JKBJiHZ5jo #RSESpapers Stacey Martin & Susan Hough https://t.co/hz1uosClX3 pic.twitter.com/n2N6nblQui — ANU Earth Sciences 🌏 (@anuearthscience) July 14, 2022 Given the larger magnitude and farther west location of this 2021 Haiti quake relative to the 2010 earthquake, it is also worth noting the short time elapsed between the last historical sequence of large quakes on this fault. Fig from our 2012 paperhttps://t.co/zLQ8wSbtWr pic.twitter.com/ux17G6bz2F — Austin Elliott (@TTremblingEarth) August 14, 2021 Why was there a gap between the 2010 and 2021 Haiti earthquakes? Because a sequence of moderate quakes in 1860 released strain in the gap! https://t.co/rpuXfEw78G — Dr. Susan Hough 🦖 (@SeismoSue) July 15, 2022 I was excited to see & have a chance to comment on a study published in Science yesterday, discussed here. The response to the 2021 Nippes, Haiti, earthquake was very different from the response in 2010, 1/https://t.co/y6l3jjsAYQ — Dr. Susan Hough 🦖 (@SeismoSue) March 11, 2022 Saturday's M7.2 earthquake in Haiti was close to the 2010 M7.0 earthquake. Both events are devastating on their own but compounded by ongoing problems the region faces. Compare @IRIS_EPO's Teachable Moments: 2010 M7.0: https://t.co/FgYVeGH6Zy 2021 M7.2: https://t.co/z007x1QxC4 pic.twitter.com/VpkCSo90G2 — Southern California Earthquake Center (@SCEC) August 16, 2021 Here is a comparison of Peak Ground Acceleration (perceived shaking) for the January 2010 M7.0 and August 2021 M7.2* events. Note the notable difference at Port-au-Prince. #Haiti #Earthquake *ShakeMap (version 5) remains preliminary and subject to USGS updates. pic.twitter.com/AiH2FU1NeU — Steve Bowen (@SteveBowenWx) August 14, 2021
A few days ago, I was passed out on my couch (sleep apnea) and for some reason I awoke and noticed that I had gotten a CSEM notification of a large earthquake offshore of Alaska. Well, after looking into that, I sent my boss, Rick, a text message: “8.2.” So let’s take a look at the things that may have affected the size of the tsunami from this 2021 M 8.2 earthquake. Below is an educational video from the USGS that presents material about subduction zones and the 1964 earthquake and tsunami in particular. This is a map from Haeussler et al. (2014). The region in red shows the area that subsided and the area in blue shows the region that uplifted during the earthquake. These regions were originally measured in the field by George Plafker and published in several documents, including this USGS Professional Paper (Plafker, 1969).
Above: Rupture zones of earthquakes of magnitude M > 7.4 from 1925-1971 as delineated by their aftershocks along plate boundary in Aleutians, southern Alaska and offshore British Columbia [after Sykes, 1971]. Contours in fathoms. Various symbols denote individual aftershock sequences as follows: crosses, 1949, 1957 and 1964; squares, 1938, 1958 and 1965; open triangles, 1946; solid triangles, 1948; solid circles, 1929, 1972. Larger symbols denote more precise locations. C = Chirikof Island. Below: Space-time diagram showing lengths of rupture zones, magnitudes [Richter, 1958; Kanamori, 1977 b; Kondorskay and Shebalin, 1977; Kanamori and Abe, 1979; Perez and Jacob, 1980] and locations of mainshocks for known events of M > 7.4 from 1784 to 1980. Dashes denote uncertainties in size of rupture zones. Magnitudes pertain to surface wave scale, M unless otherwise indicated. M is ultra-long period magnitude of Kanamori 1977 b; Mt is tsunami magnitude of Abe[ 1979]. Large shocks 1929 and 1965 that involve normal faulting in trench and were not located along plate interface are omitted. Absence of shocks before 1898 along several portions of plate boundary reflects lack of an historic record of earthquakes for those areas.
Proposed tectonic model for southern Chile. Partitioning of the oblique convergence vector between the Nazca plate and South American plate results in a dextral strike-slip fault zone in the magmatic arc and a northward moving forearc sliver. Modified after Lavenu and Cembrano (1999).
In 2016, there was an earthquake along the Alaska Peninsula, a M 7.1 on 2016.01.24. Here is my earthquake report for this earthquake. Here is a map for the earthquakes of magnitude greater than or equal to M 7.0 between 1900 and today. This is the USGS query that I used to make this map. One may locate the USGS web pages for all the earthquakes on this map by following that link. I plot tide gage data for gages in the north and northeast Pacific Ocean. These data are from NOAA Tides and Currents, though are also available via the eu tide gage website here. The scale for the tsunami wave height is on the right side of the chart. Below are surface deformation data generated by the USGS based on their finite fault model. The three panels show surface deformation in the north, east, and vertical directions. 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.
Digitized marigrams from 1938 Alaskan earthquake recorded in Crescent City, San Diego, and San Francisco. The tidal componenht asn ot beenr emoved.S tartt ime listedf or each record is the time in minutes from the origin time of the earthquaketo the startt ime of the digitizedr ecord.
Location of subfaults used in inversion of tsunami waveforms. Graph shows slip distribution in meters.
Observed and synthetic waveforms from inversion for four subfaults. Start time of each record is different. The arrows indicate the parts of the waveforms used for the inversion.
Example slip distributions for two of the slip models, shallow eastern and shallow far eastern. For each model the slip is the product of a function f(x) representing the along-strike variation and g(y) representing the downdip variation, and then scaled to a constant magnitude MW 8.25. The functions f(x) and g(y) are based on relations in Freund and Barnett [1976]. For the central and western models, the rupture area is the same as for the eastern model, but the area of higher slip is shifted to the west. For the mid-depth and deep models, the main area of high slip is shifted downdip.
Vertical seafloor displacements caused by representative slip scenarios. On the left side, the slip is concentrated in the east and the deep, mid-depth and shallow slip distribution scenarios are shown. On the right, the Western, Central and Far Eastern slip distribution scenarios are shown assuming the shallow rupture. Displacements are in meters. Red contours show depth to the plate interface from 0 to 80 km with a 10 km increment.
Tide gauge data and model predictions for the eastern and far eastern source models.
Here is an animation from one of the Ferymueller et al. (2021) models for the 1938 M 8.2 tsunami.
A) Location of Chirikof Island within the plate tectonic setting of the Alaska-Aleutian subduction zone. Rupture areas for great twentieth century earthquakes on the megathrust are in pink. (B) Velocity field of the Alaska Peninsula and the eastern Aleutian Islands observed by global positioning system (GPS) (Fournier and Freymueller, 2007). Colors show inferred rupture areas for earthquakes in 1788 (green) and 1938 (orange). Both A and B are modified from Witter et al. (2014). The section of the megathrust between Kodiak Island and the Shumagin Islands has been referred to as the Semidi segment (e.g., Shennan et al., 2014b). (C) Physiography of Chirikof Island (Google Earth image, 2012) showing the location of our study area at Southwest Anchorage, a prominent moraine, a fault scarp (facing southeast) that probably records the 1880 earthquake, the New Ranch valley reconnaissance core site, and UNAVCO GPS station AC13 (http:// pbo .unavco .org /station /overview /AC13). In the eighteenth and nineteenth centuries, Chirikof Island was known to native Alutiiq and Russians as Ukamuk Island.
Age probability distributions for probable (red) and possible (orange) tsunami deposits at Southwest Anchorage (labels as in Fig. 11) compared with age distributions for possible tsunami deposits at Sitkinak Island (Briggs et al., 2014a) and with age estimates for great earthquakes and tsunamis on Kodiak Island (from studies referenced on this figure; #EarthquakeReport for M8.2 #Earthquake and probable #Tsunami offshore of #Alaskahttps://t.co/mFtEoigFQB read more about the tectonics herehttps://t.co/L4RHgNdex7 pic.twitter.com/Kgp6HxzSQ6 — Jason "Jay" R. Patton (@patton_cascadia) July 29, 2021 From @BNONews — Desianto F. Wibisono (@TDesiantoFW) July 29, 2021 #EarthquakeReport preliminary interpretive poster for M 8.2 #Earthquake #tsunami offshore of #Alaska in region 1938 M 8.2 generated #Tsunami with wave hts 5-10cm in #California (Johnson and Satake, '96)https://t.co/mFtEoigFQB — Jason "Jay" R. Patton (@patton_cascadia) July 29, 2021 Watch the waves from the M8.2 earthquake just offshore Alaska roll across the seismic stations in North America. (Credit @IRIS_EPO) pic.twitter.com/8qQeV4qBZY — Dr. Kasey Aderhold (@KaseyAderhold) July 29, 2021 Here's the #USGS MT for the recent M 8.2 on Fig. 1 of Freymueller et al. 2021 (https://t.co/FN8owbDqEY). Orange outline is aftershocks of the 1938 M 8.2. Red lines are 1 m contours of 1938 slip models. Grey is slip deficit inferred from geodesy. Obvious similarities 1938 -> 2021! pic.twitter.com/DIUh4YVhXc — Rich Briggs (@rangefront) July 29, 2021 UPDATE: The timing and form of this signal looks like it is the DART response to the seismic waves directly from the earthquake, NOT to a tsunami wave. pic.twitter.com/bxeF5TPqjv — Anthony Lomax 😷🇪🇺🌍 (@ALomaxNet) July 29, 2021 Small tsunami waves continue arriving at Sand Point & other coastal areas of Alaska. Tomorrow these waves will create swirly currents in boat harbors up & down the west coast, so tie up your boats real good. pic.twitter.com/nofvKqJoU5 — Brian Olson (@mrbrianolson) July 29, 2021 And since I have a drone workshop to attend tomorrow, I will bow out now and get some sleep. — Jascha Polet (@CPPGeophysics) July 29, 2021 @NOAA Tsunami Warning System has issued a tsunami watch for the West Coast. The warning for Hawaii has been cancelled, because the waves are focused east of Hawaii and the event isn't that large. @NWS_NTWC pic.twitter.com/h2KRBmOKNL — Dr. Lucy Jones (@DrLucyJones) July 29, 2021 A Tsunami Warning remains in effect. A Tsunami Advisory also remains in effect. pic.twitter.com/QLTiROkiri — NWS Anchorage (@NWSAnchorage) July 29, 2021 What a tsunami warning sounds like… they tested this earlier today too but this time is for real! M8.2, looks like on the subduction zone interface. (and look at those pretty peonies! 🌸) pic.twitter.com/1HPy8tBUC2 — Dr. Kasey Aderhold (@KaseyAderhold) July 29, 2021 Records of tsunami deposits show significant tsunamis in 1788, 1880 and 1938 (https://t.co/NsFfTuqigs), indicating recurrence intervals of large earthquakes in the Semidi segment every 58-92 years. We are now 83 years since 1938, so that seems roughly consistent. pic.twitter.com/CGIM40Fv0g — Dr Stephen Hicks 🇪🇺 (@seismo_steve) July 29, 2021 #EarthquakeReport for M 8.2 #Earthquake and #Tsunami offshore of #Alaska updated poster with Sand Point tide gage data@USGS_Quakes slip model — Jason "Jay" R. Patton (@patton_cascadia) July 29, 2021 Preliminary finite fault for this morning's M8.2 earthquake is available. Rupture primarily to the NE of the hypocenter, away from the Shumagin Gap.https://t.co/dVkYuR2kPC pic.twitter.com/idGBqxRhbX — Dr. Dara Goldberg (@dara_berg_) July 29, 2021 All #Tsunami alerts for the #Alaska coastline have been cancelled. Remember, strong and unusual currents may continue for several hours. If you have damage, please report it to your local officials. Stay safe, get some rest, and we'll keep the watch for you. Good night. https://t.co/wzUBu4ysK3 — NWS Tsunami Alerts (@NWS_NTWC) July 29, 2021 Tonight's M8.2 event occurred close to the rupture area of the 2020 M7.8 earthquake and was the largest U.S. earthquake in 50 years. We'll continue to update as this sequence unfolds, but here is a short piece on our website with what we know so far. https://t.co/PzHaaQ8Zbl pic.twitter.com/vcM8fq9IV7 — Alaska Earthquake Center (@AKearthquake) July 29, 2021 Some Perryville M 8.2 thoughts: One of the arresting things about Chirikof coastal geology is that the island is clearly sinking like a stone today, evident in geodesy and coastal geology. Figure from Nelson et al. 2015 https://t.co/vGKDp0WYuN *BUT* that isn't the entire story pic.twitter.com/LAWLqE1Su3 — Rich Briggs (@rangefront) July 29, 2021 The two closest sites to the M8.2 Alaska earthquake today show some decent surface wave signals. There are several other closer sites that should give us better insight. @UNAVCO pic.twitter.com/lN22i7arEP — Brendan Crowell (@bwcphd) July 29, 2021 8.2 Earthquake is the largest in Alaska since 1965. I was sitting in the upper wheelhouse of my 125' steel schooner ALEUTIAN EXPRESS at Chignik Harbor and the whole boat bounced and vibrated for about a minute. 14' range of gradual Tsunami one foot every 4 minutes both directions pic.twitter.com/IlYox48ejg — John Clutter (@AleutianExpress) July 29, 2021 Interesting look at the tide gauge in Eureka this morning. That perturbation over the last couple of hours is likely associated with the small tsunami waves from Alaska. This is a great reminder that tsunami danger can last well after the specific 'arrival time' #cawx pic.twitter.com/JloflW8aa5 — NWS Eureka (@NWSEureka) July 29, 2021 Additional Information about the M 8.2 earthquake that occurred 50 miles south of the Alaska Peninsula last night. https://t.co/2Jn2DLAV8M #Earthquake #Alaska pic.twitter.com/s1DDPmmaXG — USGS (@USGS) July 29, 2021 Alaska has a M7 earthquake every 2 years on average. So why the big deal about this M8.2? There is a BIG DIFFERENCE between a M7 and a M8. Use this “spaghetti magnitude” scale to visualize the difference. #AlaskaQuake pic.twitter.com/DT3tBzRkxs — Dr. Wendy Bohon (@DrWendyRocks) July 29, 2021 Preliminary Finite Fault Model of the Mw 8.2 Alaska event. @dara_berg_ @geosmx pic.twitter.com/WZNgmu9HWo — Sebastian Riquelme (@accelerogram) July 29, 2021 Clear NE propagation from the M8.2 in Alaska, but look at 102 sec- action to E way updip by the trench. Early aftershock or where rupture finally expired? It's small amplitude, but coherent and seen by 4 very different arrays. I await better analyses.https://t.co/6hFfZ64Elw pic.twitter.com/hacucSnOil — Alex Hutko (@alexanderhutko) July 29, 2021 Good morning all! The tsunami waves are still bouncing around the Aleutian Islands in Alaska (max height measured was ~2 feet). The tsunami turned out not to be very big & all @NWS_NTWC alerts for the US west coast are CANCELLED. 🚨NO alerts for CA, OR, WA. #earthquake pic.twitter.com/uEHSdzzvv9 — Brian Olson (@mrbrianolson) July 29, 2021 Waves from the recent M8.2 #Alaska #earthquake rolling through North America. Different colors correspond to different types of seismic waves. @IRIS_EPO pic.twitter.com/RJBlGh7zFg — UMN Seismology (@UMNseismology) July 29, 2021 Good morning PNW- ICYMI, last night there was a M8.2 earthquake off the Alaska Peninsula. Here, you can see waves from it (bottom) compared to a nearby Alaskan M6.8 (top, similar to our 2001 Nisqually M6.8) at station LEBA near the SW Washington coast. pic.twitter.com/GCCAjbYpII — PNSN (@PNSN1) July 29, 2021 Here I show the cross-section through the Alaska seismicity with projected mechanisms. The largest two events are yesterday's M8.2 quake and last year's M7.8, both subduction interface events. For reference, a cartoon of the shallow subduction zone from https://t.co/Gces1m71C8 pic.twitter.com/bgchTpPT5n — Jascha Polet (@CPPGeophysics) July 29, 2021 You may not have felt it, but a groundwater well in Washington County, Maryland did! An 8.2 magnitude earthquake rocked southern Alaska overnight and the water level in our well sloshed almost a foot. https://t.co/kafsMsaaph. For more real-time well data https://t.co/w56ACDNk4h pic.twitter.com/87fVSz0MLz — @USGS_MD_DE_DC (@USGS_MD_DE_DC) July 29, 2021 15 second sample rate data for AB13 is now available for the M8.2 Alaska earthquake, we see a pretty appreciable SE offset with 10 cm of subsidence. The event started NE of AC12 and ruptured to the NE, so this site is in the middle of it all. @UNAVCO pic.twitter.com/8nTTZstIDX — Brendan Crowell (@bwcphd) July 30, 2021 The largest earthquake to hit the U.S. in the last few decades took place in Alaska yesterday. The Mw 8.2 quake broke the Aleutian megathrust in the Shumagin seismic gap. The rupture did not propagate to the trench, causing only a minor tsunami. Figure by @QQtecGeodesy pic.twitter.com/02ylFet8P6 — Sylvain Barbot (@quakephysics) July 30, 2021 Recent Earthquake Teachable Moment for the M8.2 #AlaskaEarthquakehttps://t.co/2sFE9QDrNb pic.twitter.com/aLtYLIm61i — IRIS Earthquake Sci (@IRIS_EPO) July 30, 2021 14+ hours after the #alaska earthquake and there is still a tsunami bouncing around at the closest tide gauge (small tsunami) pic.twitter.com/3xtjS4hhge — Bill Barnhart (@SeismoSARus) July 29, 2021 There was a bit of confusion and misinformation with the Alaska earthquake last night, so how about us geoscientists put together a thread of seismologists/tsunami experts to follow. I'll start: @CPPGeophysics @SeismoSue @seismo_steve #Earthquake #alaskaearthquake pic.twitter.com/nfbQvfbnQy — Dr Janine Krippner (@janinekrippner) July 29, 2021 As of 12 hours following the M8.2 we've located ~140 aftershocks. The locations and magnitudes are subject to change upon further review, but look to be occurring to the east of 2020 sequence. The map here shows 2020 in gray and the recent aftershocks in red. pic.twitter.com/hQ93k7HVUZ — Alaska Earthquake Center (@AKearthquake) July 29, 2021 Last night's magnitude 8.2 earthquake serves as a powerful reminder of the restlessness of our planet's surface—and it presents an exciting opportunity to peer deeper at our planet’s inner workings. Learn more about Alaska's shakes in my latest @NatGeo https://t.co/gnPANhqWW1 — Dr. Maya Wei-Haas (@WeiPoints) July 29, 2021 Our event page for last night's M8.2 earthquake in Alaska is posted and will be updated as data are made available: https://t.co/XSq1nVyBuU pic.twitter.com/NcUqOKBdGT — UNAVCO (@UNAVCO) July 29, 2021 Slip contours for the July 2020 and 2021 megathrust #earthquakes One begins where the other ends. @bwcphd @dara_berg_ pic.twitter.com/URdqVX2r2R — Sean (@tsuphd) July 29, 2021 (1/3) The "Lame Monster": Today's largest US earthquake in >50 years did not make a large tsunami. Why? These are computer models of the tsunami from the M8.3 earthquake in Alaska#AlaskaQuake #alaskatsunami pic.twitter.com/QlJSWJMaqG — Amir Salaree (@amirsalaree) July 29, 2021 🌊The entire #California coast is a #tsunami hazard area. 🌊The July 27 M8.2 earthquake in #Alaska generated minor tsunami waves that are still being recorded on tide gages here. 🌊Head to ➡️https://t.co/UUkQsqYcAk to learn more about your tsunami risk. pic.twitter.com/pHjrTeOv5o — California Department of Conservation (@CalConservation) July 30, 2021 GPS receivers can be used as seismometers. In blue are the 5 Hz velocities recovered on Kodiak Island with the variometric approach for the M8.2 earthquake yesterday. In red, the collocated accelerometer, S19K, downsampled to 5 Hz. pic.twitter.com/jxJR1v7Fj1 — Brendan Crowell (@bwcphd) July 30, 2021 A notable characteristic of the M8.2 Alaska earthquake is that it was relatively deep and doesn’t appear to have ruptured the shallow plate boundary. Could overpressured sediments on the shallow plate boundary inhibited shallow slip? Check out this seismic image updip of event. pic.twitter.com/HRQEPxrAZk — Donna Shillington (@djshillington) July 30, 2021 We finally have some preliminary coseismic offsets for the M8.2 Alaska earthquake. AB13 has a 43 cm offset to the SE. pic.twitter.com/RSttwW4nBl — Brendan Crowell (@bwcphd) July 30, 2021 While the M8.2 was the largest earthquake in the U.S. in 50 years, Alaska has experienced some significantly sized events during that time. The plot here shows the largest Alaska earthquake magnitude each year since 1964. Since 2000, we're experienced at least a M6.4 annually. pic.twitter.com/Iq9pFanPqi — Alaska Earthquake Center (@AKearthquake) July 30, 2021 Whopper M8.2 earthquake in Alaska moved GPS stations, revealing the broad pattern and extent of deformation. — Bill Hammond (@BillCHammond) July 30, 2021 (1/6) DART Seismology: How the tsunami sensors near Alaska picked up the seismic surface waves from the M8.3 Alaska earthquake! The tails in the records are mixes of surface waves and the tsunami.#alaskaearthquake #alaska_tsunami @NOAAResearch @NWS_PTWC @IRIS_EPO pic.twitter.com/OWI7e47dNq — Amir Salaree (@amirsalaree) July 31, 2021 #EarthquakeReport and #TsunamiReport for M8.2 #Earthquake offshore of #Alaska updated interpretive poster '21 sequence matches '38 sequence for both ~slip patch and ~tsunami size https://t.co/pE3zA9HHFShttps://t.co/mFtEoigFQB — Jason "Jay" R. Patton (@patton_cascadia) August 2, 2021 #Sentinel1 co-seismic interferograms (ascending track) over western Alaska, show ground deformation towards the southern coast, above the main M8.2 #earthquake fault rupture. Aftershock epicenters (yellow) from USGS. pic.twitter.com/RtavuJZGSZ — Sotiris Valkaniotis (@SotisValkan) August 2, 2021 The M 8.2 Chignik earthquake that occurred off the Alaskan Peninsula on July 28 was the largest US earthquake in 50 years. This 2013 simulation from the same region shows how a hypothetical M 9.1 (almost 30x stronger!) earthquake can create a far-reaching tsunami. @USGS_Quakes pic.twitter.com/tLtxWxoal7 — USGS Coastal Change (@USGSCoastChange) July 30, 2021 Updated finite fault model (joint inversion of regional and teleseismic data) is now available: https://t.co/K0kXumE6Pv pic.twitter.com/y7Z9vIF6Lu — Dr. Dara Goldberg (@dara_berg_) August 3, 2021 #EarthquakeReport & #TsunamiReport for M8.2 Perrysville #Earthquake and transpacific #Tsunami updated poster including @USGS_Quakes @dara_berg_ updated slip model also, surface deformation data I prepared a report and will update morehttps://t.co/y1RwyZjKOA pic.twitter.com/lj8qIk7vQl — Jason "Jay" R. Patton (@patton_cascadia) August 4, 2021
I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events. This year we look back and remember what happened ten years ago in Japan and across the entire Pacific Basin. Here are all the pages for this earthquake and tsunami: I have several reports from previous years that have reviews of the earthquake and tsunami. I focus mostly on new material I prepared for the following report. Use this map to see the magnitudes of different earthquakes experienced in Japan. The map shows earthquake epicenters for large-magnitude historic events of the past century. It also includes epicenters for all aftershocks and triggered earthquakes for a year after the M 9.1 earthquake, and an outline of the aftershocks, which illustrates the area of the fault that slipped during the M 9.1 earthquake. Earthquake intensity is a measure of how strongly earthquake shaking is felt by people and objects. The further away from the epicenter, the lower the earthquake intensity. Seismologists use computer models to estimate what the intensity will be from an earthquake. The U.S. Geological Survey uses its “Did You Feel It?” (DYFI) system to collect observations about how strongly people in different places felt an earthquake. Use this map to see the level of intensity people felt in different parts of Japan. The map displays the USGS intensity model for the M 9.1 earthquake as transparent colors. The map also shows, as colored circles, the “Did You Feel It?” report results from people who experienced shaking from this earthquake. 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. Use this map to see tsunami wave data as recorded by tide gages across the entire Pacific Basin. Click on a white triangle and there is a link to open the tide gage data as a graphic. 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. #EarthquakeReport for #OTD 2011 M9.1 Tōhoku-oki #Earthquake #Tsunami #Landslides decade remembrance with some updated maps and web maps report here:https://t.co/n5UI6Co1iv main report w/tectonic details:https://t.co/0jo9XuHxdE pic.twitter.com/MkEAbQkTXe — Jason "Jay" R. Patton (@patton_cascadia) March 11, 2021 #EarthquakeReport #OTDearthquake 2011.03.11 M 9.0 Tohoku-oki earthquake and tsunami. #JapanEarthquake first observed 50+ m slip, fault offset at trench, heatflow from fault-slip friction, triggered outer-rise EQs etc. Many discoveries MORE here:https://t.co/0jo9XuHxdE pic.twitter.com/6gNFZWitDn — Jason "Jay" R. Patton (@patton_cascadia) March 11, 2018
Yesterday as I was signing into work, my colleague Jackie Bott (a seismologist, seismic hazard/geology mapper, and on my tsunami team at CGS) mentioned the outer rise earthquake offshore of Chile that caused a small tsunami.
PAGER provides shaking and loss estimates following significant earthquakes anywhere in the world. These estimates are generally available within 30 minutes and are updated as more information becomes available. Rapid estimates include the number of people and names of cities exposed to each shaking intensity level as well as the likely ranges of fatalities and economic losses.
Yesterday’s M 6.4 is a strike-slip earthquake (look at the earthquake mechanism legend on the top center of the poster) and appears to have slipped along the Petrinja fault. This fault has different names in different papers (which is common), but this name comes from the European Database of Seismogenic Faults. 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.
Location of the South Balkan extensional system (SBER) withing the eastern European region. The system today is within the southern Balkan region north of the North Anatolian fault (NAF), shown by the horizontal line patter. Retreating subduction zones and related backarc extensional areas for the Mediterranean region are shown in blue , and advancing subduction zones an related are a of backarc shortening are shown in red). Backarc extensional regions are shown by dotted pattern. KF = Kefalonia fault zone.
Map of the most important seismogenic faults
Digital terrain model of the Pannonian basin to show its position within the Alpine mountain belt and the location of different subunits.
Block model depicting the present position of the Alcapa and Tisza-Dacia terranes in the Carpathian embayment and the associated lithospheric and asthenosphericprocesses down to the upper mantle transition zone (inspired after Ustaszewski et al., 2008).
Map of the Neogene Pannonian Basin, showing depocenters of the subbasins. The associated Transylvanian (TR) and Vienna (V) basins are shown. Modified from Horvath (1985a).
Tectonic map of the Pannonian Basin and surrounding regions showing the main extensional faults of Neogene age. After Rumpler and Horvath (1988). Area of Pannonian Basin Tertiary rocks within the Alpine-Carpathian fold belts shown as white.
Model geometry and boundary conditions used in the finite element procedure. Note that a larger framework was created to minimize edge effects and errors. As a result, the ‘free’ edges are buffered but can be deformed on a small scale. For further discussion see text. The Adria–Europe rotation pole was taken from Ward (1994).
Best-fitting resultant stress pattern reflecting the combined effects of the applied boundary conditions (see insets), changing crustal thickness and two predefined weakness zones. (a), ( b) The edge at the Bohemian Massif is fixed and slightly deforming, respectively. In order to make direct comparison possible, the smoothed (observed) and calculated stress directions are superimposed.
Cartoon summarizing the main stress sources in the Alpine–Carpathian–Pannonian–Dinaric system applied in our finite element models. Buttresses are rigid crustal blocks indenting or blocking their surroundings. Dashed lines represent faults that were included during modelling. The kinematics of some major faults showing present-day activity are also shown (after Gerner et al. 1997) 1: Molasse belt; 2: Flysch belt; 3: internal units; 4: Neogene and Quaternary #EarthquakeReport poster for M6.4 strike-slip #Earthquake in #Croatia https://t.co/nWCoPdKZ68 high chance for liquefaction likely ruptured the Petrinja fault, thought to be capable of M6.5 eventshttps://t.co/4Agp4cBnrz pic.twitter.com/TLJkADieQZ — Jason "Jay" R. Patton (@patton_cascadia) December 30, 2020 today's epicenter of the earthquake pic.twitter.com/OTZN5jrRWJ — Tomislav Kelekovic (@tkelekovic) December 29, 2020 Here is some more liquefaction on video https://t.co/EPOygT9shI — Marko (@Marko61511524) December 29, 2020 Photo of a sand boil(?) (indicating subsurface liquefaction) from the M6.4 #CroatiaEarthquake near #Petrinja. Seismic shaking increases pressure in water-filled pores between sand grains until the lose contact w/ each other, start acting like liquid (Photo from @LastQuake app) pic.twitter.com/09aoP2Hl03 — Brian Olson (@mrbrianolson) December 29, 2020 Preliminary automatic scenario of expected permanent deformations for the M 6.4 #Croatia #Earthquake. Waiting for other solutions and, of course, InSAR data. With @antandre71 pic.twitter.com/I78q9lpJ1Z — Simone Atzori (@SimoneAtzori73) December 29, 2020 #ERCC #DailyMap: 2020-12-30 ⦙ <p>Croatia | 6.4M Earthquake of 29 December</p> ▸https://t.co/OWf76WHpXL pic.twitter.com/Y4YsXLxEIy — Copernicus EMS (@CopernicusEMS) December 30, 2020 Best candidate fault structure for today's M6.4 #earthquake near Petrinja & Sisak, Croatia; NW-SE trending Petrinja fault zone (red arrows – HRCS027 in SHARE db) clearly visible in the terrain morphology. Epicenters (yellow) from @EMSC, foc mechs from GFZ. pic.twitter.com/dgeCep2ZUF — Sotiris Valkaniotis (@SotisValkan) December 29, 2020 This video compilation of footage from the M6.3 in Croatia has quite a number of remarkable perspectives, including — Austin Elliott (@TTremblingEarth) December 30, 2020 Sentinel-1 coseismic interferogram of the M6.3 Petrinja/Sisak earthquake #potres from ascending track @SotisValkan @EricFielding @gfun @LastQuake @JosipStipcevic pic.twitter.com/wreomZH1QG — Marin Govorcin (@Govorcin) December 30, 2020 M6.4 Petrinja, Croatia (2020.12.29)https://t.co/J82bValkmu Sentinel path 146 (2020.12.24-2020.12.30) pic.twitter.com/NfLG80tLWJ — gCent (@gCentBulletin) December 30, 2020 #EarthquakeReport for M6.4 #Earthquake in #Croatia #CroatiaEarthquake videos confirm liquefaction as suggested by USGS #liquefaction susceptibility model tectonic background here:https://t.co/ie8S2LGJeT pic.twitter.com/01ZKZD5bAI — Jason "Jay" R. Patton (@patton_cascadia) December 31, 2020 Magnitude 6.4 Earthquake in Croatia Kills at Least 7, Cuts Power and Water for Tens of Thousands https://t.co/Zaxkke9Dyg — Democracy Now! (@democracynow) December 31, 2020 #Sentinel-1 co-seismic deformation map and 3D displacement view (exaggerated) of 29.12.2020 M 6.4 #Petrinja, #Croatia #earthquake. Positive values (blue) indicate upward displacements. InSAR data obtained from COMET-LiCS database. pic.twitter.com/rGCO2otqHG — Reza Saber (@Geo_Reza) December 31, 2020 Today's 2020-12-29 M6.4 #Croatia #earthquake waves as seen from #Europe's #seismograph network via Ground Motion Visualization. The video does not reflect the actual speed of the waves. Time is shown at the bottom right. Code by @IRIS_EPO, with some preprocessing. @EGU_Seismo pic.twitter.com/EJAtqyqAFb — Giuseppe Petricca (@gmrpetricca) December 29, 2020 Enough with pain, loss and disasters in 2020. — Asieh Namdar (@asiehnamdar) December 30, 2020 #30Dicembre #30December #December30 2020 Earthquake Mw 6.4 Shakemovie – Animations of seismic wave propagation on the earth's surface (source INGV Italy)#earthquake #potres #terremoto #Petrinja #Croatia #Croazia #Hrvatska pic.twitter.com/4UeO74zwkT — geocappiello (@geocappiello) December 30, 2020 The largest onshore earthquake rupture in Europe since Norcia 2016. Copernicus #Sentinel1 co-seismic interferogram (ascending) for the M6.4 Petrinja, Croatia #earthquake. Shallow NW-SE 15-20km rupture along the fault scarp just west of Petrinja. pic.twitter.com/kB5bTuFV5X — Sotiris Valkaniotis (@SotisValkan) December 30, 2020 A number of large #landslides were triggered (with a few cm of displacement) by the M6.4 Petrinja, Croatia #earthquake – identifiable in the #Sentinel1 interferogram in distances as far as 30km from the earthquake rupture. pic.twitter.com/BBR8lgjwCH — Sotiris Valkaniotis (@SotisValkan) December 31, 2020 A damaging M6.4 #earthquake rattled #Croatia today, centered near Petrinja. It appears to have struck on a strike slip fault. This quake came a day after a M5.2 quake struck just to the northwest. Today’s quake was felt throughout the region. https://t.co/Zhezg7qu4U — temblor (@temblor) December 29, 2020 Efforts to assess the damage from yesterday’s magnitude-6.4 earthquake in Central Croatia continue. https://t.co/tMTXrys1RH — temblor (@temblor) December 30, 2020 — Marin Govorcin (@Govorcin) December 31, 2020 Here is a newly received picture following #CroatiaEarthquake It is liquefaction. Please read previous tweets for explanations pic.twitter.com/2iTjSse1Co — EMSC (@LastQuake) January 1, 2021 #EarthquakeReport update for #Croatia #CroatiaEarthquake #Earthquake see aftershocks and intensities for both 22 March '20 M 5.3 and 29 Dec '20 M 6.4 events the rest of the original report:https://t.co/ie8S2LGJeT pic.twitter.com/JnVzX7xmzI — Jason "Jay" R. Patton (@patton_cascadia) January 3, 2021 [Update] We're studying the evolution of the #Croatia #seimic sequence after the #earthuqake a few days ago, and thought it could be worthwhle to share. — iunio iervolino (@iuniervo) January 2, 2021 A bit of #MondayDataViz. — Dr Stephen Hicks 🇪🇺 (@seismo_steve) January 4, 2021 Report on the M6.4 Petrinja #earthquake, Croatia (29/12/2020), by the Geological Survey of Croatia https://t.co/L3gRZztvZm pic.twitter.com/NLmJukz4m3 — Stéphane Baize (@stef92320) January 4, 2021 Aftershocks of this week’s damaging M6.4 #Petrinja #earthquake are migrating onto a mapped fault that cuts through the capital city of #Zagreb. https://t.co/bA9j0UARKp — temblor (@temblor) January 2, 2021 🗺 New map: [#EMSR491] Petrinja Town: Grading Product, version 1, release 1, Vector Package [v1, 1:] — Copernicus EMS (@CopernicusEMS) December 31, 2020
I awakened to be late to attending the GSA meeting today. I had not checked the time. 7am is too early, but i understand the time differences… To the north is a strike-slip plate boundary localized along the North Anatolia fault system. This is a right lateral fault system, where the plates move side by side, relative to each other. See the introductory information links below to learn more about different types of faults.
Seismicity of the Eastern Mediterranean region and surroundings reported by USGS–NEIC during 1973–2007 with magnitudes for M . 3 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).
Tectonic map of the Aegean and eastern Mediterranean region showing the main plate boundaries, major suture zones, fault systems and tectonic units. Thick, white arrows depict the direction and magnitude (mm a21) of plate convergence; grey arrows mark the direction of extension (Miocene–Recent). Orange and purple delineate Eurasian and African plate affinities, respectively. Key to lettering: BF, Burdur fault; CACC, Central Anatolian Crystalline Complex; DKF, Datc¸a–Kale fault (part of the SW Anatolian Shear Zone); EAFZ, East Anatolian fault zone; EF, Ecemis fault; EKP, Erzurum–Kars Plateau; IASZ, Izmir–Ankara suture zone; IPS, Intra–Pontide suture zone; ITS, Inner–Tauride suture; KF, Kefalonia fault; KOTJ, Karliova triple junction; MM, Menderes massif; MS, Marmara Sea; MTR, Maras triple junction; NAFZ, North Anatolian fault zone; OF, Ovacik fault; PSF, Pampak–Sevan fault; TF, Tutak fault; TGF, Tuzgo¨lu¨ fault; TIP, Turkish–Iranian plateau (modified from Dilek 2006).
Present-day kinematic and tectonic map encompassing the Central and Eastern Mediterranean, summarizing our main results and interpretations. Our kinematic model includes rigid-block motions as well as localized and distributed strain. Central-SW Aegean block (CSW AEG block) and East Anatolian block (East Anat. block) are purely kinematic and directly results from strain modeling (Figure 5). AP-IO Block is our Apulian-Ionian block with tentative tectonic boundaries. Rotation pole of this Apulian-Ionian block relative to Nubia (Nu WAp-Io) and to Eurasia (Eu WAp-Io) are shown with their 95% confidence ellipse.
Geological map showing the distribution of the Menderes Extensional Metamorphic Complex (MEMC), Oligocene–Miocene volcanic and sedimentary units and volcanic centers in the Aegean Extensional Province (compiled from geological maps of Greece (IGME) and Turkey (MTA), and adapted from Ersoy and Palmer, 2013). Extensional deformation field with rotation (rotational extension) is shown with gray field, and simplified from Brun and Sokoutis (2012), Kissel et al. (2003) and van Hinsbergen and Schmid (2012). İzmir–Balıkesir Transfer zone (İBTZ) give the outer limit for the rotational extension, and also limit of ellipsoidal structure of the MEMC. MEMC developed in two stages: the first one was accommodated during early Miocene by the Simav Detachment Fault (SDF) in the north; and the second one developed during Middle Miocene along the Gediz (Alaşehir) Detachment Fault (GDF) and Küçük Menderes Detachment Fault (KMDF). Extensional detachments were also accommodated by strike-slip movement along the İBTZ (Ersoy et al., 2011) and Uşak–Muğla Transfer Zone (Çemen et al., 2006; Karaoğlu and Helvacı, 2012). Other main core complexes in the Aegean, the Central Rhodope (CRCC), Southern Rhodope (SRCC), Kesebir–Kardamos Dome (KKD) and Cycladic (CCC) Core Complexes are also shown. The area bordered with dashed green line represents the surface trace of the asthenospheric window between the Aegean and Cyprean subducted slabs (Biryol et al., 2011; de Boorder et al., 1998). See text for detail.
Mantle flow pattern at Aegean scale powered by slab rollback in rotation around vertical axis located at Scutary-Pec (Albania). A: Map view of fl ow lines above (red) and below (blue) slab. B: Three-dimensional sketch showing how slab tear may accommodate slab rotation. Mantle fl ow above and below slab in red and blue, respectively. Yellow arrows show crustal stretching.
A: Tectonic map of the Aegean and Anatolian region showing the main active structures
C: GPS velocity field with a fixed Eurasia after Reilinger et al. (2010) D: the domain affected by distributed post-orogenic extension in the Oligocene and the Miocene and the stretching lineations in the exhumed metamorphic complexes.
E: The thick blue lines illustrate the schematized position of the slab at ~150 km according to the tomographic model of Piromallo and Morelli (2003), and show the disruption of the slab at three positions and possible ages of these tears discussed in the text. Velocity anomalies are displayed in percentages with respect to the reference model sp6 (Morelli and Dziewonski, 1993). Coloured symbols represent the volcanic centres between 0 and 3 Ma after Pe-Piper and Piper (2006). F: Seismic anisotropy obtained from SKS waves (blue bars, Paul et al., 2010) and Rayleigh waves (green and orange bars, Endrun et al., 2011). See also Sandvol et al. (2003). Blue lines show the direction of stretching in the asthenosphere, green bars represent the stretching in the lithospheric mantle and orange bars in the lower crust.
G: Focal mechanisms of earthquakes over the Aegean Anatolian region.
Input GPS velocities of the model. Velocities are in Eurasia fixed reference frame with their respective 95% confidence ellipse. Velocity vectors are color coded relative to the study they have been taken from (see paper for more details). (a) GPS velocities of the entire Nubian plate used to constrain the Nubia–Eurasia relative motion. Nubia–Eurasia rotation pole defined in this and previous studies are shown with their 1s confidence ellipse: circle, Calais et al. [2003]; diamond, Le Pichon and Kreemer [2010]; open square, D’Agostino et al. [2008]; triangle, Argus et al. [2010]; filled square, Reilinger et al. [2006]; red star, present study. Parameters of these rotation poles are summarized in Table 2. (b) Focus on the GPS velocities in the Central and Eastern Mediterranean region.
Input seismic moment tensors of the model. Fault plane solutions are from the Harvard CMT catalog (from 1976 to 2007) and the Regional Centroid Moment Tensor (RCMT) catalog (from 1995 to 2007). Location and hypocenter depth of the events are relocalized according to the Engdahl et al. [1998] catalog.
Outline geological map of western Anatolia showing Neogene and Quaternary basins [simplified from Bingo1 (1989).
Simplified geological map of the northern margin of the Btiytik Menderes Graben in the area between Germencik and Umurlu.
Geological cross-section of the northern margin of the Bt~yt~k Menderes Graben (see Fig. 6b for location) based on fig. llb of Cohen et al. (1995). This cross-section indicates a total of c. 5 km of extension. Assuming a uniform extension rate, the age of the fault zone is (c. 5 km/1 mm a -1) 5 Ma. More details in the paper.
Geology map of the study area (simplified from MTA 1: 500,000 scale geology map) and location of the seismic lines. Active faults are marked onland with bold lines.
Time migrated seismic sections, offshore Teke and Karaburun, showing active normal faults marked with white lines and strike-slip faults with black lines (see Fig. 3A for locations). Vertical exaggeration is ~2. Observed vertical displacement on the seafloor and basement surface by normal fault (marked with bold circle on Line-10) looks the same, thus this normal fault is Quaternary age. On line-18, vertical displacement seen on basement units are greater than displacement on Pliocene–Quaternary deposits due to fault marked with a bold circle thus this normal fault can be interpreted as Later Miocene–Pliocene age.
(A) The correlations between offshore and onshore active fault systems in the study region. N–S, NE–SW and NW–SE oriented lines and dashed-lines show interpreted active strike-slip faults and their possible extensions. These faults are annotated with dNT for those at north and dST for those at south. E–W oriented lines and dashed lines show interpreted active normal faults and their possible continuations, with footwalls indicated by the plus symbol. (B) Simplified active fault map of the study area. The bold lines show the master active faults. (C) Pureshear model can explain the development of active structures in the study area.
Geological map of western Turkey showing the Menderes massif and its subdivision into the AG Alasehir graben, the BMG Büyük Menderes graben, the CMM Central Menderes massif, the KMG Küçük Menderes graben, the NMM Northern Menderes massif and the SMM Southern Menderes massif, modified from Sengör and Bozkurt (2013).
(a) A conceptual model of geothermal circulation in the study area, (b) a deep seismic profile with the N–S direction taken from a 30 km west of study area (Nazilli region) (Çifçi et al., 2011). Roman numerals indicate the different sedimentary sequences.
Simplified geological map of the KMG showing the positions of geological cross-sections.
Series of geological cross-sections showing various sectors of the KMG depicting horst and graben structures overprinted onto the huge synclinal structure (see Fig. 3 for positions of geological cross-sections).
Schematic tentative cross-sections showing the Miocene to Quaternary evolution of the KMG (modified from Erinç [66]). Note the continuing extension since Miocene.
Simplified tectonic map of the Mediterranean region showing the plate boundaries, collisional zones, and directions of extension and tectonic transport. Red lines A through G show the approximate profile lines for the geological traverses depicted in Figure 2. MHSZ—mid-Hungarian shear zone; MP—Moesian platform; RM—Rhodope massif; IAESZ— Izmir-Ankara-Erzincan suture zone; IPS—Intra-Pontide suture zone; ITS—inner Tauride suture zone; NAFZ—north Anatolian fault zone; KB—Kirsehir block; EKP—Erzurum-Kars plateau; TIP—Turkish-Iranian plateau.
Simplified tectonic cross-sections across various segments of the broader Alpine orogenic belt.
Late Mesozoic–Cenozoic geodynamic evolution of the western Anatolian orogenic belt as a result of collisional #EarthquakeReport for #Earthquake #Deprem and #Tsunami in the eastern #AegeanSea offshore of #Turkey poster is now updated with aftershocks from @LastQuake report here:https://t.co/vNuRdWw0Gs pic.twitter.com/SnYXwg2n3T — Jason "Jay" R. Patton (@patton_cascadia) October 31, 2020 #EarthquakeReport #TsunamiReport for M7 offshore of #Turkey small sized tsunami observed across the #AegeanSea https://t.co/i1lZJ0pkb3 analog event in 2017 and more tectonic background herehttps://t.co/jwwXh0SpXl pic.twitter.com/sk1HVbbCKD — Jason "Jay" R. Patton (@patton_cascadia) October 30, 2020 Unfortunately, with the source so close to the coast, any Tsunami Early Warning System (#TEWS) has little room to warn the population in advanced to save lives. Prepareness/education is then the key ingredient. — Jorge Macías Sánchez (@JorgeMACSAN) October 30, 2020 İzmir #deprem Alaçatı #tsunami #deliklikoy pic.twitter.com/Fo74diHpBJ — ulaş tuzak (@ulastuzak) October 30, 2020 M6.9 #earthquake (#deprem) strikes 66 km SW of #İzmir (#Turkey) 21 min ago. Updated map of its effects: pic.twitter.com/Kh3WMz6Hxi — EMSC (@LastQuake) October 30, 2020 Video forwarded by a friend pic.twitter.com/P5g7H7LInn — Tiernan Henry (@tiernanhenry) October 30, 2020 I'd be cautious. A similar EQ occurred offshore Bodrum, SW Turkey, in 2017 (Mw 6.6). Many assumed it ruptured the big mapped normal fault, but careful analysis showed it ruptured a smaller conjugate fault that would've been missing from this database. https://t.co/zEKYatNi1O — Edwin Nissen (@faulty_data) October 30, 2020 #deprem geçmiş olsun İzmir 2020 son hızıyla devam ediyor. pic.twitter.com/cZc3rgWV0e — jojomiyo (@jojomiyo1) October 30, 2020 Fully automatic processing (beta-version) of the expected permament deformation and #InSAR fringes for the M 7.0 #earthquake in #dodecanese (#Greece), 11:51 (UTC). Focal mechanism from USGS, both nodal planes used. With @antandre71 pic.twitter.com/TQiaoDgYf7 — Simone Atzori (@SimoneAtzori73) October 30, 2020 Absolutely terrible scenes coming out of Turkey after the M7.0 earthquake. My thoughts are with all of the people impacted by this event. 💔 https://t.co/gs8Wj8Cj5a — Dr. Wendy Boo – hon 👻 (@DrWendyRocks) October 30, 2020 The October 30 M7 EQ offshore Samos Island, Greece, occurred as the result of normal faulting at a shallow crustal depth within the Eurasia tectonic plate in the E Aegean Sea. This indicates N-S oriented extension that is common in the Aegean Sea. 🍫 https://t.co/r5i9Ni1S1B pic.twitter.com/C6CyLDOlZ1 — USGS Earthquakes (@USGS_Quakes) October 30, 2020 Η #Σάμος άντεξε στο τρομακτικό μέγεθος των 6,7 ρίχτερ ευτυχώς δεν έχουμε θύματα!! #Σεισμός pic.twitter.com/Sd00bTBOd5 — Θεοδόσης Ζερβουδάκης (@tzervoudakis) October 30, 2020 El terremoto de Turquía de hace un rato llevó a un desastre tremendo. Uno que se da por la falta de preparación ante algo así, sobre todo en la parte ingenieril. Tendrá magnitud 7, pero a 10 km de profundidad golpea fuerte a las ciudades cercanas, que estaban mal paradas pic.twitter.com/vomUd3Xauu — Cristian Farías (@cfariasvega) October 30, 2020 30 Ekim 2020 #Seferihisar açıkları (#İzmir)/Sisam (M6.6/6.9) #depremi anaşokundan itibaren 1.0 ile 5.1 arasında değişen toplam 85 deprem oldu. Depremler D-B doğrultulu normal fay boyunca dağılım göstermektedir. pic.twitter.com/65ULhiqEq2 — Dr. Ramazan Demirtaş (@Paleosismolog) October 30, 2020 İzmir'de su seviyesi yükseldi. Tsunami benzeri görüntüler ortaya çıkıyor.#deprem pic.twitter.com/dbxCCgks5C — Politikaloji🇹🇷 (@politikaloji) October 30, 2020 Location of Samos Mw7 #earthquake on Aegean Sea seismo-tectonic sketch. In yellow, grabens / major extension zones. Today's earthquake happened on a major normal fault bounding one of these grabens. Map from Armijo et al. GJI, 1996 pic.twitter.com/qx46D6peTS — Robin Lacassin (@RLacassin) October 30, 2020 Seferihisar'da tsunami… — FORUM ATMOSFER (@forumatmosfer) October 30, 2020 Watch the waves from the M7.0 #earthquake near Turkey roll across seismic stations in Europe. https://t.co/SoZMmJHvCU (THREAD) pic.twitter.com/8YKQHaj2yf — IRIS Earthquake Sci (@IRIS_EPO) October 30, 2020 Map of extension responsible for today's Mw 7.0 earthquake in the Aegean (red star). GPS vectors show motion relative to Anatolia plate. NW Turkey moves N, SW Turkey moves S, so western Turkey stretches N-S. Graph shows how W Turkey opens up like spreading the fingers of a hand pic.twitter.com/JpWklc7YZY — Edwin Nissen (@faulty_data) October 30, 2020 🌊🇬🇷 Vathí es otra localidad al norte de la isla de #Samos que también registró los efectos del tsunami, inundando las zonas más baja de la ciudad. Se observan estragos menores en el registro. Vídeo: @atta_fareid pic.twitter.com/CnZzN6c48l — EarthQuakesTime (@EarthQuakesTime) October 30, 2020 More @NERC_COMET LiCSAR results for yesterday's Aegean earthquake, including filtered/unwrapped interferograms and kmz files for viewing in google earth: https://t.co/TY8ijrUoml — Tim Wright (@timwright_leeds) October 31, 2020 Helpful map showing tectonic setting of today's M7.0 #IzmirEarthquake (yellow dot). The African Plate is subducting under the South Aegean/Anatolian Plate, which is extending as it overrides. The fault that broke today is a "pull-apart" fault (normal fault). #EarthquakeIzmir pic.twitter.com/31Hw4EFWze — Brian OLSON (@mrbrianolson) October 30, 2020 30 Ekim 2020 / İzmir pic.twitter.com/OYzy0n9hF5 — Son Dakika TV (@sondakikativi) October 30, 2020 GPS velocity & direction of surface monitoring stations in the area of today's M7.0 #IzmirEarthquake showing SSW-directed extension towards the African Plate. The stations near the epicenter are moving ~0.9 – 1.3 inches per year (relative to stable African P.) Data via @UNAVCO pic.twitter.com/iVJJO93Gtl — Brian OLSON (@mrbrianolson) October 30, 2020 Today's Mw 7.0 #earthquake near the Greek island of Samos ruptured near the Menderes Graben in Western Turkey, a region with a long history of strike-slip and normal faulting. pic.twitter.com/9FiOreCK2R — Sylvain Barbot (@quakephysics) October 30, 2020 #EarthquakeReport for #Earthquake #Deprem and #Tsunami in the eastern #AegeanSea offshore of #Turkey poster is now updated with aftershocks from @LastQuake report here:https://t.co/vNuRdWw0Gs pic.twitter.com/SnYXwg2n3T — Jason "Jay" R. Patton (@patton_cascadia) October 31, 2020 AGGIORNAMENTO: Terremoto Mw 7.0 a Nord di Samos (Grecia) del 30 ottobre 2020 https://t.co/pnhYLioLb1 — INGVterremoti (@INGVterremoti) October 30, 2020 It is a bit late in the game, but here is a simulation of yesterdays Turkey/Greece tsunami: pic.twitter.com/HrSnsCl2mA — Amir Salaree (@amirsalaree) October 31, 2020 My thoughts are with the bereaved, injured and homeless after yesterday's earthquake in Turkey. The size of the quake is shown on these responses from @raspishake seismometers across the globe. The plot is made using @obspy. pic.twitter.com/wrD1Xhfcx8 — Mark Vanstone (@wmvanstone) October 31, 2020 Map of ground displacements calculated from @CopernicusData Sentinel-1 radar (InSAR) by NASA-JPL ARIA project. Western Samos island moved up (blue tones), small area of coast moved down (red) due to M7.0 earthquake yesterday. Other areas affected by atmosphere. pic.twitter.com/26rFem82YN — Eric Fielding (@EricFielding) October 31, 2020 Jason, also the ~1 days @LastQuake aftershocks distribution seems to be in agreement with the positive stress change related to the @usgs preliminary finite fault model pic.twitter.com/7FNr52Aat2 — Jugurtha Kariche (@JkaricheKariche) October 31, 2020 The red curve below represents the intensity (i.e. shaking and damage level) vs epicentral distance for yesterday M7 #Izmir #Samos #earthquake #deprem. The blue dots are individual felt reports shared by eyewitnesses via LastQuake app. — EMSC (@LastQuake) October 31, 2020 Preliminary teleseismic finite fault model of the 30 Oct Mw 7 Greece #earthquake for both planes. Method= Ji et al. (2002). Here rupture started from the KOERI hypocenter (H=10 km). Rupture moved bilaterally; most of the high slip and its peak located up-dip in the shallow depth. pic.twitter.com/7E4jpwJzvu — Dimas Sianipar (@SianiparDimas) November 1, 2020 Regional tectonics of the area where the M7.0 Samos #earthquake occurred pic.twitter.com/XaWmKMsrlA — IRIS Earthquake Sci (@IRIS_EPO) November 2, 2020 A bit of lunchtime #dataviz. — Stephen Hicks 🇪🇺 (@seismo_steve) November 2, 2020 Damage Proxy Map from ARIA shows surface changes that may be due to damage measured with radar images. Maps on NASA Disasters Portal: https://t.co/Q4JA2ezU8R — Advanced Rapid Imaging & Analysis (ARIA) (@aria_hazards) November 2, 2020 The "GEER-069: 2020 #Samos Island (Aegean Sea) #earthquake Report" by @HAEE_ETAM, @DepremVakfi, #TDMD, @EERI_tweets and #GEER has been published and is available online (https://t.co/7pb7V8kSMx) ! pic.twitter.com/zpNehqIrTg — EQUIDAS (@equidas) January 3, 2021
Earthquake Report: M 6.9 Mid Atlantic Ridge
Earthquake magnitude is controlled by three things:
If we continue to look at the historic record, we will see that there appear to be three instances where one of these M 6.5-7 earthquakes had a later earthquake of a similar magnitude.
When an earthquake fault slips, the crust surrounding the fault squishes and expands, deforming elastically (like in one’s underwear). These changes in shape of the crust cause earthquake fault stresses to change. These changes in stress can either increase or decrease the chance of another earthquake.
I wrote more about this type of earthquake triggering for Temblor here. Head over there to learn more about “static coulomb stress triggering.”
In the poster, I label these earthquakes as “Linked Earthquakes.” Perhaps the later of each earthquake pair (or triple) was triggered by the change in static coulomb stress.
Here are the three sets of “Linked Earthquakes:”
Since we cannot yet know the real answer to this question, we are reminded of the advice that educators and emergency response people provide: If one lives in Earthquake Country, get earthquake prepared. Just a little effort to get better prepared makes a major difference in the outcome.
Head over to Earthquake Alliance where there are some excellent brochures about how to be better prepared and more resilient to earthquake and tsunami hazards. Living on Shaky Ground is one of my favorites!Below is my interpretive poster for this earthquake
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
Atlantic
General Overview
Earthquake Reports
Social Media
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: M 7.5 in Peru
Below is my interpretive poster for this earthquake
I include some inset figures.
Chile | South America
General Overview
Earthquake Reports
Social Media
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report Lite: M 7.0 near Acapulco, Mexico
Below is my interpretive poster for this earthquake
I include some inset figures.
Tide Gage Data – Acapulco
Earthquake Intensity
Mexico | Central America
General Overview
Earthquake Reports
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: M 7.2 in Haiti
Below is my interpretive poster for this earthquake
I include some inset figures.
Earthquake Aftershocks
Potential for Ground Failure
Caribbean
General Overview
Earthquake Reports
Social Media
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: M 8.2 near Perryville, Alaska
https://earthquake.usgs.gov/earthquakes/eventpage/us6000f02w/executive
Rick Wilson runs the tsunami program at the California Geological Survey (CGS) and works with the California Governor’s Office of Emergency Services (Cal OES) to use official forecasts of tsunami size from the National Tsunami Warning Center (NTWC) to alert coastal emergency managers about the level of potential evacuation that they may want to act upon.
More about this process can be found here. Take a look at the CGS Special Report 236 to learn about the Tsunami Playbooks and the “FASTER” approach for tsunami evacuation guidance. Evacuation is something that is done at the local level, so CGS and Cal OES can only provide recommendations.
Needless to say, we were both at the ready to respond. Rick has hourly phone calls with the NTWC and follows up with phone calls and emails to specific interested parties (e.g. the emergency managers). We each went into tsunami response mode. I manage the Tsunami Event Response Team, which may be activated to collect observations of tsunami inundation or ocean currents.
I started looking at tide gage and DART Buoy data to see how large the tsunami was in the epicentral region. The M 8.2 was in the region of the 1938 M 8.2 earthquake which generated a transoceanic tsunami. I also looked into the literature about the 1938 tsunami, to see what size that tsunami was. The 1938 tsunami had a decimeter scale wave height (peak to trough) for gages in Alaska and in California (Johnson and Satake, 1994). Jeff Freymueller et al. (2021) had also recently worked on the 1938 earthquake source area and tsunami modeling as well.
The nearest tide gage for this 2021 event is at Sand Point, but the nearest gage in 1938 was in Unalaska. So, in order to get a modest comparison between 1938 and 2021, I felt a need to wait for the Unalaska data to trickle in. This may give us some idea whether the 1938 tsunami recorded in Crescent City and San Francisco might be a decent analogue. Of course, we need to get the official forecast from the NTWC prior to sending out any information. But, that process can take hours (over 3 hours in this case). So, we need to get our minds wrangled around the possibilities in the absence of more information.
Earthquake and Tectonic Background:
The plate boundary in the north Pacific is a convergent (pushing together) plate boundary where the Pacific plate on the south ‘subducts’ northwards beneath the North America plate on the north. The Alaska-Aleutian subduction zone forms a deep sea trench which can be seen in maps of the region. The subduction zone fault dips into the Earth, getting deeper to the north.
Between earthquakes (the interseismic period), the megathrust fault is seismogenically coupled (i.e. ‘locked’) just like velcro has the ability to hold together one’s wallet. The plates are always moving towards each other. Because the fault is locked, the crust surrounding the fault bends elastically to accommodate this convergent motion.
As the crust bends and flexes, it stores energy (i.e. tectonic strain). The part of the fault closest to the seafloor (the southernmost part of this subduction zone fault) gets pulled downwards, while the part of the crust further to the north flexes upwards.
The materials along the earthquake fault have properties that resist motion (like the velcro). But, as the plates converge and increase the amount of energy stored, the forces on the fault may exceed the strength of the fault. At this time, the fault slips, causing an earthquake.
The part of the fault that was being pulled downwards gets pushed upwards during the earthquake (the coseismic period), while the crust that was being flexed upwards between earthquakes thus subsides downwards during the earthquake.
The Alaska-Aleutian subduction zone has a history of subduction zone earthquakes and tsunami, plus there exists a prehistory of earthquakes and tsunami in some parts of this plate boundary. Geologists are often asked to determine the potential hazard of future earthquakes and tsunami and their answers are based on what we know from the past (using both historic and prehistoric data).
The 2021 M 8.2 earthquake happened in the same location as a 1938 M 8.2 earthquake, just to the east of a sequence of earthquakes from last year (22 July and 19 October 2020).
Tsunami:
When the earthquake fault slips, and the upper plate deforms, the vertical motion of the plate can elevate (or lower) the overlying ocean water. After the water changes position, it seeks to return to sea-level (an equipotential surface). If elevated, the water drops downwards and then oscillates up and down. This is the process that generates waves that radiate from the area with seafloor deformed by the earthquake.
Things that make a tsunami larger are [generally]:
First of all, based on the earthquake slip models (estimates of how the earthquake slipped, in meters, and how that slip varied along the fault) suggest that a majority of the largest slip happened beneath the continental shelf. The water depth on the shelf is similar to many shelfs worldwide, shallower than about 200 meters. How does this affect the size of the tsunami?
Well, I guess that is the main point, the ground deformation that generated the tsunami was beneath shallow water.
These slip models are based on a variety of data and most of the data are seismic data. Some tsunami are generated by slow slip (not generating seismic waves) on the shallow part of the fault. These are called tsunami earthquakes.
Because tsunami earthquakes may be generated by slip in this way, slip models using seismic data cannot resolve the location of the slip on the fault that created these tsunami. However, the tsunami from this 2021 M 8.2 earthquake were small. Therefore the updip part of the fault probably did not contribute significantly to the tsunamigenic ground deformation.Below is my interpretive poster for this earthquake
I include some inset figures. Some of the same figures are located in different places on the larger scale map below. I present 3 posters, each with slightly different information.
Tectonic Overview
Youtube Source IRIS
mp4 file for downloading.
Credits:
Here is a cross section showing the differences of vertical deformation between the coseismic (during the earthquake) and interseismic (between earthquakes).
This figure, from Atwater et al. (2005) shows the earthquake deformation cycle and includes the aspect that the uplift deformation of the seafloor can cause a tsunami.
Here is a figure recently published in the 5th International Conference of IGCP 588 by the Division of Geological and Geophysical Surveys, Dept. of Natural Resources, State of Alaska (State of Alaska, 2015). This is derived from a figure published originally by Plafker (1969). There is a cross section included that shows how the slip was distributed along upper plate faults (e.g. the Patton Bay and Middleton Island faults).
Here is a graphic showing the sediment-stratigraphic evidence of earthquakes in Cascadia, but the analogy works for Alaska also. Atwater et al., 2005. There are 3 panels on the left, showing times of (1) prior to earthquake, (2) several years following the earthquake, and (3) centuries after the earthquake. Before the earthquake, the ground is sufficiently above sea level that trees can grow without fear of being inundated with salt water. During the earthquake, the ground subsides (lowers) so that the area is now inundated during high tides. The salt water kills the trees and other plants. Tidal sediment (like mud) starts to be deposited above the pre-earthquake ground surface. This sediment has organisms within it that reflect the tidal environment. Eventually, the sediment builds up and the crust deforms interseismically until the ground surface is again above sea level. Now plants that can survive in this environment start growing again. There are stumps and tree snags that were rooted in the pre-earthquake soil that can be used to estimate the age of the earthquake using radiocarbon age determinations. The tree snags form “ghost forests.
This is a photo that I took along the Seward HWY 1, that runs east of Anchorage along the Turnagain Arm. I attended the 2014 Seismological Society of America Meeting that was located in Anchorage to commemorate the anniversary of the Good Friday Earthquake. This is a ghost forest of trees that perished as a result of coseismic subsidence during the earthquake. Copyright Jason R. Patton (2014). This region subsided coseismically during the 1964 earthquake. Here are some photos from the paleoseismology field trip. (Please contact me for a higher resolution version of this image: quakejay at gmail.com)
This is another video about the 1964 Good Friday Earthquake and how we learned about what happened.
Tsunami Data
Each plot includes three datasets:
Note the all tsunami wave height plots are the same vertical scale, except for Sand Point.
I measured the largest wave heights for each site, displayed in yellow.
Alaska
Here are the data from the DART buoy nearest the M 8.2. People often mistake these data for tsunami data, but this is generated by seismic waves.
One way to test one’s hypothesis about whether these buoy data are seismic waves or tsunami waves, one simply need to take a look at the time that the wave begins to be recorded by the DART buoy.
Seismic waves travel through water at about 1.5 kms per second. While tsunami wave velocity (based on the shallow water wave equation) for depths ranging from 200-4000 meters is between ~0.02 to 0.2 kms per second, much slower than seismic waves.
Surface Deformation
North, East, and Up are positive (blue) while South, West, and Down are negative (red).
Note the upper panel and how the Pacific plate is moving to the north and the North America is moving south. Does this make sense?
The middle panel is interesting too, but skip to the lower panel, vertical. The accretionary prism (forming the continental slope), directly above the aftershocks and mainshock, rises up during the earthquake. The upper North America plate landward of the slip patch subsides. Does this make sense?
Earlier in this report we took a look at the geologic evidence for megathrust subduction zone earthquakes, evidence that records this “coseismic” subsidence.
Shaking Intensity and Potential for Ground Failure
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.
Some Relevant Discussion and Figures
Fig. 1). Dotted horizontal lines show our correlation of evidence for some younger earthquakes and tsunamis. Times of great earthquakes inferred from episodes of village abandonment determined from archaeological stratigraphy in the eastern Alaska-Aleutian megathrust region are also shown (Hutchinson and Crowell, 2007).
Alaska | Kamchatka | Kurile
General Overview
Earthquake Reports
Social Media
BREAKING: Tsunami sirens sound in Kodiak, Alaska after a major magnitude 8.2 earthquake struck off the coast; risk being evaluated for the Pacific pic.twitter.com/amxpLGX70s
tectonic background:https://t.co/L4RHgNdex7 pic.twitter.com/uQ2ur85EaC
My initial guess that today's event may have been similar to the 1938 M8.2 earthquake still looks like it has some merit.
Follow https://t.co/A1MNRg1WKF for updates on tsunami warnings. pic.twitter.com/g4qME2w0SI
tsunami prehistory and history for region doi:10.1130/GES01108.1https://t.co/mFtEoigFQB
more background here https://t.co/L4RHgNdex7 pic.twitter.com/HXpQUVSWFE
B/c most of elastic energy was released deeper in the Earth.
Stations near Denali NP ~900 km moved a few mm… See https://t.co/4zpOW4m1pJ for more info and data. pic.twitter.com/j1GSIazVfJ
tectonic background here:https://t.co/L4RHgNdex7 pic.twitter.com/iTMmm5u2LQ
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report M 6.7 in Panama
Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here.
https://earthquake.usgs.gov/earthquakes/eventpage/us6000exs5/executiveBelow is my interpretive poster for this earthquake
I include some inset figures.
Mexico | Central America
General Overview
Earthquake Reports
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.
Earthquake Report: Tōhoku-oki Earthquake Ten Years Later
There are numerous web experiences focused on this type of reflection. Here is a short list, some of which I have been involved in.
Updated Interpretive Poster
I include some inset figures.
Seismicity
Web Map
Earthquake Intensity
Web Map
Tsunami
We think that the earthquake slipped at least 50 meters (165 feet) during several minutes. This is the largest coseismic measurement of any subduction zone earthquake (so far).
When the fault slipped, it caused the seafloor to deform and move. This motion also displaced the overlying water column.
As the water column is elevated, it gains potential energy. As this uplifted water expends this energy by oscillating up and down, it radiates energy in the form of tsunami waves.
Tsunami were observed across the entire Pacific Basin, causing extensive damage and casualties in Japan, but also in other places too. There was about $100 million damage to coastal infrastructure in California alone.
This is an animated model of the Great East Japan tsunami of ten years ago. The warmer the colors, the larger the wave. The first surges reached the closest Japan coasts in about 25 minutes. The first surges reached Crescent City in 9.5 hours. (modified text from Dr. Lori Dengler)
This is the same map used as an overlay in the web map below.
Here is the tide gage record from Crescent City, California, USA.
Time is represented by the horizontal axis and elevation is represented on the vertical axis. The darker blue line in this image represents NOAA’s tidal forecast. The data recorded by the tide gage are represented by the light blue colored lines. Wave height is the distance measured between the wave crest and trough. Wave amplitude is the level of water above sea level.
Some of these data came from the IOC sea level monitoring website.
Web Map
There is an overlay of color that represents the size of the tsunami as it travelled across the ocean. Learn more about these data here.
Ground Failure
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.
Use this map to see the magnitudes of different earthquakes experienced in Japan. The map shows earthquake epicenters for large-magnitude historic events of the past century. It also includes epicenters for all aftershocks and triggered earthquakes for a year after the M 9.1 earthquake, and an outline of the aftershocks, which illustrates the area of the fault that slipped during the M9.1 earthquake.
Web Map
Japan | Izu-Bonin | Mariana
General Overview
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check out the tide gage plots, about 50 of them
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Earthquake Report: Croatia!
https://earthquake.usgs.gov/earthquakes/eventpage/us6000d3i9/executive
I checked this out and found a 20 cm wave height tsunami observed on a tide gage directly east of the earthquake epicenter. This was interesting as the earthquake was an “outer rise” event (seaward of the subduction zone trench, where the Nazca plate flexes downward prior to being subducted.
As the plate flexes downward, the upper part of the plate gets stretched and extensional faults can form here (or cause pre-existing faults to be reactivated as extensional/normal faults). For more background about different types of faults, head here: Earthquake Plate Tectonic Fundamentals page.
And, this M 6.7 earthquake was a normal fault earthquake (based on the earthquake mechanism). The largest tsunami waves can be generated by landslides or subduction zone faults, but other fault types can generate tsunami too (albeit smaller in size). Interesting indeed (there is more, like it is in a region of a triggered outer rise events following the 1960 M 9.5 Chile earthquake; is this M 6.7 an aftershock?, probably not).
BUT, this earthquake report is about the earthquake in Croatia that Jackie also mentioned in her email. Upon quick review, looking at the USGS PAGER Alert page, I knew that there was a high likelihood for casualties.
https://earthquake.usgs.gov/earthquakes/eventpage/us6000d3zh/executive
According to the database, the Petrinja fault is capable of a M 6.5 earthquake.Below is my interpretive poster for this earthquake
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
UPDATE: 2021.01.03 Aftershocks and Intensity Comparison.
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Shaking Intensity and Potential for Ground Failure
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.
Seismic Hazard and Seismic Risk
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Some Relevant Discussion and Figures
volcanites; 5: Pieniny Klippen Belt; 6: strike-slip faults; 7: normal faults; 8: thrust faults.
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Focal mechanism from GFZ Geofon (https://t.co/6E9hLx3oaI), both planes are considered.
*on a lake*
*inside a church*
*on a street with bricks toppling*
*across from a damaged barn crumbling*
and … on a cooking show?https://t.co/TvihBKsdov
EQ Intensity exceed MMI 8
Petrinja, Croatia – one day after a destructive and deadly earthquake.#CroatiaEarthquake
📷 Antonio Bronic pic.twitter.com/aNzfueKWO1
Petrinja, Croatia 🇭🇷
Local time 12:19:54 2020-12-29
Earthquake caught on live camera during interview about earthquakes at Trending Views
potential magnitudes from eg https://t.co/4Agp4cBnrz
[Data source @EMSC; elaborations @robBaras] pic.twitter.com/VOMpUKCevx
Temporal evolution of the foreshock and aftershock sequences associated with last week's magnitude 6.4 Croatia earthquake. pic.twitter.com/F68nSP4QOg
🔗 https://t.co/4JoOJLRoIm — #earthquake #grading in #Croatia#Copernicus #CEMS #RapidMapping #EUCivPro
References:
Basic & General References
Specific References
earthquake and its strongest aftershock of 24 May 1979 (Mw 6.2) in Tectonophysics, v. 421, p. 129-143, http://dx.doi.org/10.1016/j.tecto.2006.04.009Return to the Earthquake Reports page.
Earthquake Report: Turkey!
As i was logging into Zoom, my coworker emailed our Tsunami Unit group about a M7 in the eastern Mediterranean. So, I shifted gears a bit. But i had my poster to present, so i had to stay somewhat focused on that.
https://earthquake.usgs.gov/earthquakes/eventpage/us7000c7y0/executive
Today, in the wee hours (my time in California), there was a M 7.0 earthquake offshore of western Turkey in the Icarian Sea. The earthquake mechanism (i.e. focal mechanism or moment tensor) was for an extensional type of an earthquake, slip along a normal fault.
I immediately thought about some quakes/deprems that happened there several years ago. This area is an interesting and complicated part of the world, tectonically.
To the south is a convergent plate boundary (plates are moving towards each other) related to (1) the Alpide Belt, a convergent plate boundary formed in the Cenozoic that extends from Australia to Morocco. On the southern side of Greece and western Turkey, there are subduction zones where the Africa plate dives northward beneath the Eurasia and Anatolia plates.
The region of today’s earthquake is in a zone of north-south oriented extension. This extension appears to be in part due to gravitational collapse of uplifted metamorphic core complexes.
There are several “massifs” that were emplaced in the past, lifted up, creating gravitational potential. The normal faults may have formed as the upper crust extended. It is complicated here, so i am probably missing some details. But, with the references i provide below, y’all can read more on your own. Feel free to contact me if i wrote something incorrect. I love my peer reviewers (you).
So, this N-S extension creates east-west oriented valleys/basins with E-W striking (trending) faults. There are south dipping faults on the north sides and north dipping faults on the south side of these valleys.
These structures are called rifts. A famous rift is the East Africa Rift.
There are two main rifts in western Turkey, the Büyük Menderes Graben and the Küçük Menderes Graben Systems. If we project these rifts westward, we can see another rift, the rift that forms the Gulf of Corinth in Greece, the Gulf of Corinth Rift. This is one of the most actively spreading rifts in the world.
In addition to the large earthquake, which caused lots of building damage and also caused over a dozen deaths so far (sadly), there was recorded a tsunami on the tide gages in the region. I use the IOC website to obtain tide gage data. This is an excellent service. There are only a few national tide gage online websites that rival this one.
It is also highly likely that there were landslides or that there was liquefaction somewhere in the region. The USGS models i present below show a high likelihood for these earthquake triggered processes.Below is my interpretive poster for this earthquake
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
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Some Relevant Discussion and Figures
(black lines), the main sutures zones (thick violet or blue lines), the main thrusts in the Hellenides where they have not been reworked by later extension (thin blue lines), the North Cycladic Detachment (NCDS, in red) and its extension in the Simav Detachment (SD), the main metamorphic units and their contacts; AlW: Almyropotamos window; BD: Bey Daglari; CB: Cycladic Basement; CBBT: Cycladic Basement basal thrust; CBS: Cycladic Blueschists; CHSZ: Central Hellenic Shear Zone; CR: Corinth Rift; CRMC: Central Rhodope Metamorphic Complex; GT: Gavrovo–Tripolitza Nappe; KD: Kazdag dome; KeD: Kerdylion Detachment; KKD: Kesebir–Kardamos dome; KT: Kephalonia Transform Fault; LN: Lycian Nappes; LNBT: Lycian Nappes Basal Thrust; MCC: Metamorphic Core Complex; MG: Menderes Grabens; NAT: North Aegean Trough; NCDS: North Cycladic Detachment System; NSZ: Nestos Shear Zone; OlW: Olympos Window; OsW: Ossa Window; OSZ: Ören Shear Zone; Pel.: Peloponnese; ÖU: Ören Unit; PQN: Phyllite–Quartzite Nappe; SiD: Simav Detachment; SRCC: South Rhodope Core Complex; StD: Strymon Detachment; WCDS: West Cycladic Detachment System; ZD: Zaroukla Detachment. B: Seismicity. Earthquakes are taken from the USGS-NEIC database. Colour of symbols gives the depth (blue for shallow depths) and size gives the magnitude (from 4.5 to 7.6).
Those Rifts
Regional Cross Sections
necking and asthenospheric upwelling have produced locally well-developed alkaline volcanism (e.g., Sardinia). Slab tear or detachment in the Calabria segment of Adria, as imaged through seismic tomography (Spakman and Wortel, 2004), is probably responsible for asthenospheric upwelling and alkaline volcanism in southern Calabria and eastern Sicily (e.g., Mount Etna). Modified from Séranne (1999), with additional data from Spakman et al. (1993); Doglioni et al. (1999); Spakman and Wortel (2004); Lentini et al. (this volume).
and extensional processes in the upper plate of north-dipping subduction zone(s) within the Tethyan realm. See text
for discussion.
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complicated tectonics
also a plot of tide gage data from the region
Arrival times as prediceted by #Tsunami–#HySEA#IzmirEarthquake pic.twitter.com/8UEwItsLal
Deniz suyu ilçeyi kapladı…
İzmir Seferihisar'da 6.6 büyüklüğündeki depremin ardından tsunami meydana geldi.#İzmir #deprem #izmirdedeprem #Tsunami pic.twitter.com/kCugei77Zj
Unwrapped data (below) easier to interpret. Main subsidence (red) is offshore N of Samos. pic.twitter.com/eGGCHL6LXx
complicated tectonics
also a plot of tide gage data from the region
1/n pic.twitter.com/cBn4sew2xx
Aftershock sequence of the M7.0 Western Turkey as it stands.
Catalogue: @LastQuake pic.twitter.com/5oUa0fyXpL
Data also on ARIA-share: https://t.co/CDz2xn2gFo pic.twitter.com/uu5iYqi6WA
References:
Basic & General References
Specific References
Return to the Earthquake Reports page.