Earthquake Report: Taiwan Update #1

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People have been busy documenting the damage from the M 6.4 earthquake in Taiwan. Here is my initial Earthquake Report for this earthquake.

Here is the interpretive map that I put together for my initial Earthquake Report.

Here is a large scale (zoomed in) view of the region with the Modified Mercali Intensity (MMI) contours plotted. Find out more about the MMI scale here and here.

Here is a great general overview of the tectonics of the region from Shyu et al. (2005). I include their figure caption below the image as a blockquote.

A neotectonic snapshot of Taiwan and adjacent regions. (a) Taiwan is currently experiencing a double suturing. In the south the Luzon volcanic arc is colliding with the Hengchun forearc ridge, which is, in turn, colliding with the Eurasian continental margin. In the north both sutures are unstitching. Their disengagement is forming both the Okinawa Trough and the forearc basins of the Ryukyu arc. Thus, in the course of passing through the island, the roles of the volcanic arc and forearc ridge flip along with the flipping of the polarity of subduction. The three gray strips represent the three lithospheric pieces of Taiwan’s tandem suturing and disarticulation: the Eurasian continental margin, the continental sliver, and the Luzon arc. Black arrows indicate the suturing and disarticulation. This concept is discussed in detail by Shyu et al. [2005]. Current velocity vector of the Philippine Sea plate relative to the Eurasian plate is adapted from Yu et al. [1997, 1999]. Current velocity vector of the Ryukyu arc is adapted from Lallemand and Liu [1998]. Black dashed lines are the northern and western limits of the Wadati-Benioff zone of the two subducting systems, taken from the seismicity database of the Central Weather Bureau, Taiwan. DF, deformation front; LCS, Lishan-Chaochou suture; LVS, Longitudinal Valley suture; WF, Western Foothills; CeR, Central Range; CoR, Coastal Range; HP, Hengchun Peninsula. (b) Major tectonic elements around Taiwan. Active structures identified in this study are shown in red. Major inactive faults that form the boundaries of tectonic elements are shown in black: 1, Chiuchih fault; 2, Lishan fault; 3, Laonung fault; 4, Chukou fault. Selected GPS vectors relative to the stable Eurasian continental shelf are adapted from Yu et al. [1997]. A,Western Foothills; B, Hsueshan Range; C, Central Range and Hengchun Peninsula; D, Coastal Range; E, westernmost Ryukyu arc; F, Yaeyama forearc ridge; G, northernmost Luzon arc; H, western Taiwan coastal plains; I, Lanyang Plain; J, Pingtung Plain; K, Longitudinal Valley; L, submarine Hengchun Ridge; M, Ryukyu forearc basins.

This figure from Shyu et al. (2005) shows their interpretation of the different tectonic domains in Taiwan. This is a complicated region that includes collision zones in different orientations as the Okinawa Trough, Ryukyu Trench, and Manila Trench (all subduction zones) each intersect beneath and adjacent to Taiwan. I include their figure caption below the image as a blockquote.

Map of major active faults and folds of Taiwan (in red) showing that the two sutures are producing separate western and eastern neotectonic belts. Each collision belt matures and then decays progressively from south to north. This occurs in discrete steps, manifested as seven distinct neotectonic domains along the western belt and four along the eastern. A distinctive assemblage of active structures defines each domain. For example, two principal structures dominate the Taichung Domain. Rupture in 1999 of one of these, the Chelungpu fault, caused the disastrous Chi-Chi earthquake. The Lishan fault (dashed black line) is the suture between forearc ridge and continental margin. Thick light green and pink lines are boundaries of domains.

This map from Shyu et al. (2005) shows the earthquake slip regions for various historic earthquakes. I include their figure caption below the image as a blockquote.

Proposed major sources for future large earthquakes in and around Taiwan. Thick red lines are proposed future ruptures, and the white patches are rupture planes projected to the surface. Here we have selected only a few representative scenarios from Table 1. Earthquake magnitude of each scenario is predicted value from our calculation.

Here is Table 1 from Shyu et al. (2005).



Here is a map from Jascha Polet, Seismologist at Cal Poly Pomona. Dr. Polet plotted focal mechanism from historic earthquakes from this region, with the M 6.4 earthquake enlarged. These focal mechanisms are colored for depth. More on focal mechanisms is presented on my initial Earthquake Report here.

The Institute of Earth Sciences, Academia Sinica, has produced some excellent visualizations from this devastating earthquake. Below are a series of their visualizations.

This map shows their estimate of deformation due to displacement on the fault that ruptured during this earthquake. This is not a measurement of vertical deformation, but a numerical model.

This map shows their modeled estimates for ground shaking using the Modified Mercalli Intensity Scale. More on the MMI can be found here.

Another measure of the effects from an earthquake is a quantification of Peak Ground Acceleration (PGA). This refers to the maximum accelerations possibly felt at the ground surface due to shaking from the earthquake. PGA is measured in units of gravity (g) where 1 g (gal) = acceleration of gravity at sea level. While gravity varies spatially, so is generally not this value at sea level, is defined to be 9.8 m/sec^2. In the figure below, 1000 = 1 g.

Here is a cool low angle oblique version of the MMI shake map.

The following three images show the east, north, and vertical components of motion measured on seismopraphs in Taiwan.





And, my favorite, shows the seismic waves propagating across the landscape.

    Here is a video showing observations of the ground shaking, posted to yt here.

  • Here is a link to the mp4 file embedded below (6.5 MB mp4)
    Here are two videos from drone footage of the large building collapse. These were captured from news feeds on twitter. [source]

  • Here is a link to the mp4 file embedded below (0.3 MB mp4)
  • Here is a link to the mp4 file embedded below (0.3 MB mp4)
    Finally, here is some drone footage of a lateral spread (a type of landslide) triggered by the earthquake (rather, the ground shaking from the earthquake). [source]

  • Here is a link to the mp4 file embedded below (0.3 MB mp4)
    Here is a visualization of the seismic waves propagating through USArray seismometers in the USA. [source] Above is a screenshot:

  • Here is a link to the mp4 file embedded below (66 MB mp4)

This map from here shows the basement geology of Taiwan. Note the accretionary belts, including the forearc basin. This is a compilation from Teng et al. (2001) and Hsiao et al. (199Smilie: 8) as presented in Ustaszewski et al. (2012).

This shows how as additional DYFI reports were submitted, there were more reports from further distances. The upper image was acquired yesterday morning (Pacific Time) and the lower image was acquired last night (Pacific Time).



Posted in asia, College Redwoods, collision, earthquake, education, HSU, pacific, plate tectonics, subduction

Earthquake Report: Taiwan!

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We just had an earthquake in southern Taiwan. Here is the USGS website for this M 6.4 earthquake. In April 2015, there was a series of earthquakes in the northeast of Taiwan. Here is my earthquake report for those earthquakes. In 1999 there was a devastating M 7.7 earthquake in Taiwan called the Chi Chi earthquake. Here is a brief summary of this earthquake from the USGS.

Below is a map that has the epicenter located as a yellow star, with Modified Mercalli Intensity Scale contours plotted. Here is a map showing the shaking intensity that uses the Modified Mercalli Intensity (MMI) scale. The MMI scale is a qualitative scale of the ground motions. There is more about the MMI here. I place the USGS moment tensor on the map. This moment tensor suggests that this is a compressional earthquake with slight oblique motion. It is well resolved as a double couple (98%), probably due to its shallow depth. Currently, the depth is listed as 10 km (though this is a default depth, so it is probably not 10 km).

There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.

More on the complicated tectonics of this region can be found here.


This earthquake was felt broadly, including the China mainland. The colors in this map are also using the MMI color scale and are based upon reports from people who used the USGS “Did You Feel It?” (DYFI) web site. There is more about this DYFI system here.


The MMI contours in the above map are based upon numerical simulations of ground motions based upon “Ground Motion Prediction Equations.” The GMPEs are empirical relations between ground shaking intensity and distance from the earthquake. These relations are regressed for thousands of earthquakes and filtered for different geological settings. Below is a plot of the DYFI report responses (green dots are individual reports). Also shown are the GMPE estimates for ground motions based upon the models developed for the central and eastern US (orange) and for California (green). Does Taiwan “behave” more like the central and eastern US, or more like California?


Here is an oblique view of the plate configuration in this region. This is from Chang (2001).

Here is a great interpretation showing how the Island of Taiwan is being uplifted and exhumed. This is from Lin (2002).

Needless to say, this is an excellent map showing the complicated faulting of this region. This is from Theunissen et al. (2012).

Here is another tectonic interpretation map from here.

Here is a map that shows the three earthquake epicenters from 2015 as they relate to these plate boundary faults.

Here is the USGS poster for seismicity from 1900-2012 in this region. USGS Open File Report 2010-1083-M, Smoczyk et al. (2013).

Here is a plot of focal mechanisms from this region, as prepared by Jascha Polet, Professor of Geophysics at Cal Poly Pomona.


Posted in asia, College Redwoods, collision, earthquake, education, geology, HSU, pacific, plate tectonics, subduction

Earthquake Report: Kamchatka!

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We just had an earthquake located along the Kamchatka Peninsula. Here is the USGS website for this M 7.2 earthquake. This earthquake was fairly deep and approximately east of a large and very deep earthquake from 2013. Here is my earthquake report for the 2013 M 8.3 earthquake and a second report for some triggered earthquakes updip of the M 8.3.

Below I present a summary poster for this earthquake. This earthquake appears to have occurred in the downgoing Pacific plate. Below is my interpretive poster where I plot the USGS moment tensor. This earthquake is an extensional earthquake with extension in the north-south direction. The downgoing plate experiences extension in two ways, from bending in the upper part of the plate and from tension due to slab pull (as the downgoing oceanic lithosphere is pulling the plate into the mantle). The orientation of the extension during this earthquake is interesting because it is not perpendicular to the plate boundary. The 2013.05.24 M 8.3 deep earthquake was oriented in the expected direction. I also include the region of Alaska that just had a M 7.1 earthquake. Here is my Earthquake Report for the Alaska earthquake.

I include labels for the plate boundary fault systems in the region and include generic focal mechanisms for these fault systems. There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.

I include an inset map from the USGS (also included below). This map shows slip patches for some historic earthquakes. I used these slip patches to approximately place labels in green for these historic earthquakes.

I also include an inset map that shows the epicenters for historic earthquakes with USGS magnitudes greater than or equal to M 8.0. I label the dates and magnitudes of these earthquakes. Here is the query that I used to create this map. There is an interesting earthquake pair from 2006 and 2007. In 2006 there was a M 8.3 subduction zone earthquake that generated a Pacific-wide tsunami. The 2006 tsunami caused about $20 million in damage in Crescent City, CA. About a year later, there was a M 8.1 earthquake in the downgoing Pacific plate that was southeast of the trench. Dr. Erica Emery worked on this for her research.


Here is the tectonic summary poster from the USGS. This shows epicenters for earthquakes from 1900-2014, plus the slab contours from Hayes et al. (2012). These slab contours are estimate for the location of the subduction zone fault and it is based upon the 3-D location of earthquakes. There is considerable uncertainty with this model, but it is the best that we have. Hayes and his colleagues are currently updating these global slab models.


The USGS prepared a more comprehensive summary poster for this region. This poster has some plots of seismicity in cross sectional view. Here is the poster, but I include some sections of the poster below that are relevant for this earthquake.


Here is a map for the southern Kamchatka Peninsula. Earthquakes are plotted with diameter scaled to magnitude. The cross section C-C’ is labeled, as are the Hayes et al. (2012) slab contours. I place the epicenter for this earthquake as a green circle. The diameter is scaled approximately to magnitude and the location is approximate.


Here I place the hypocenter for this earthquake on the cross section from the USGS poster. The location is approximate.


Even though this is a very deep earthquake, due to its magnitude, it may lead to some casualties. Here is the PAGER alert, which is an estimate of the damage to people and their belongings (e.g. infrastructure). This is generated from a numerical model which overlays estimates of ground shaking with a geospatial database of people and infrastructure. This is only an estimate and it helps organizations plan for aid and assistance.


Here is a map from Lay et al. (2009) where they plot focal mechanisms for the 2006-2007 Kuril earthquake series. Note how the earthquakes in the Pacific plate are generally extensional. These earthquakes are in the outer rise, where the plate is flexed upward due to the forces exerted from subduction. The other interesting thing is that in 2009, there was a compressional earthquake in this same region. I include their figure caption as a blockquote.


Map showing regional bathymetry and tectonic features, along with global centroid moment tensor (CMT) solutions for the larger earthquakes in the 2006 –2007 Kuril Islands sequence (focal mechanisms), and NEIC epicenters of activity prior to the doublet (gray circles) between the two largest events (yellow circles), and following the 13 January 2007 event (orange circles). The gray shaded focal mechanisms are CMT solutions for foreshocks of the 15 November 2006 event, the red-shaded mechanisms occurred after the 15 November 2006 event, and events after 13 January 2008, including the trench slope 15 January 2009 event are green shaded. Focal mechanisms are plotted at the NEIC epicenters. The white stars indicate the CMT centroid locations for the two main shocks, which are shifted seaward relative to the NEIC locations. The arrow shows the estimated plate motion direction with a rate of 80 mm/yr computed using model NUVEL-1 [De Mets et al., 1990] with North America fixed.

Here is a map from Lay et al. (2009) that shows their interpretation of the tectonic regime of the outer rise of the Pacific plate prior to the 2006-2007 series. I include their figure caption as a blockquote.


Shallow seismicity distribution (NEIC epicenters) and all CMT solutions for events along the central Kuril Island region prior to the 15 November 2006 event. CMT centroid locations have an overall location bias somewhat toward the southeast. The approximate aftershock zones of the great 1963 Kuril Islands (Mw = 8.5) and 1952 Kamchatka (Mw = 9.0) earthquakes are outlined in red, and the epicenter of the 1915 (MS 8.0) event is shown by a red asterisk. The alongstrike extent of the 2006 –2007 great doublet is shown by the dashed red line with arrowheads. Outer rise activity of extensional or compressional nature is highlighted. The outer rise compressional mechanisms in red are from Christensen and Ruff [1988] with the 16 March 1963 event being labeled.

This shows their slip models for this earthquake pair, projected to the surface of the seafloor. I include their figure caption as a blockquote.


Surface map projection of coseismic slip for the 15 November 2006 (average slip 6.5 m) and the northwest dipping plane for 13 January 2007 (average slip 6.7 m at depths less than 25 km) events (NEIC epicenters, yellow circles, and CMT centroid epicenters, stars). Figure 15 indicates the relative position of the slip surfaces at depth. CMT mechanisms (centered on NEIC epicenters) for large events between June 2006 and May 2007 are shown; enlarged versions with first motions for the doublet events. Gray mechanisms indicate events before the 15 November 2006 event; red mechanisms indicate events after that rupture. The focal mechanism and epicenter of the 16 March 1963 (blue mechanism) and 15 January 2009 (green mechanism) compressional trench slope events (hexagons) are included. The arrow indicates the direction of the Pacific plate motion at 80 mm/yr.

Here Lay et al. (2009) present their interpretation for the earthquake cycle and how the tectonic regime changed during this period of a few decades. I include their figure caption as a blockquote.


Strain accumulation and release scenario for the great Kuril doublet. (a) During the interseismic period, the Pacific –North America (Okhotsk) plate interface is locked along the megathrust. Because of relative strength contrast between subducting and overriding plates, the elastic strain may preferentially accumulate within the elastic layer of the Pacific plate. Below the elastic layer, viscous strain accommodates the deformation and there is along-strike loading by underthrusting of the adjacent region of the arc. (b) During the 2006 earthquake, slip along the megathrust interface allows that segment of the Pacific plate to recover the accumulated slip deficit, and relaxation of accumulated compression or slab pull places the updip shallow region into an extensional strain environment causing the great 2007 extensional event. The region at the elastic-ductile transition (dotted line) deforms by viscous processes during the low strain rate interearthquake period, but will behave elastically during the high strain rate underthrusting event, helping to delay strain release in the overlying elastic lithosphere.

Posted in asia, College Redwoods, earthquake, education, geology, HSU, plate tectonics, subduction

Earthquake Animation: Gorda Plate 1900-2016 M >+ 4.5

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Following the earthquake pair today, I put together an animation showing the seismicity for this region between 1900 and 2016.01.30. I searched the USGS NEIC database for earthquakes of magnitude greater than or equal to M = 4.5. Here is my earthquake report for those earthquakes.

Here is a screenshot of the video.


Here is a download link for the video embedded below (2 MB mp4).

Here is my interpretive map for the two Gorda plate earthquakes.


Posted in cascadia, College Redwoods, earthquake, education, geology, gorda, HSU, plate tectonics

Cascadia subduction zone: M 9.0 tsunami simulation video

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NOAA Center for Tsunami Research just released an animation that shows a numerical simulation of what a tsunami may appear like when the next Cascadia subduction zone earthquake occurs. I present a summary about the CSZ tectonics on a 316th year commemoration page here. I include a yt link and embedded video and an mp4 embedded video and download link.

Here is a screenshot from the video:


    Here is the YT video:

  • This is the yt link for the embedded video below
  • Here is the mp4 video (same video):

  • This is the mp4 link for the embedded video below (15 MB mp4)

Posted in cascadia, College Redwoods, education, geology, HSU, humboldt, tsunami

Earthquake Report: Gorda!

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There was just a pair of earthquakes near the Gorda rise. There was first an earthquake of magnitude M = 5.0, followed by a M = 4.9. The 5.0 appears to be within the GP, but the 4.9 seems to be at the eastern boundary of the ridge. These two earthquakes do not pose a tsunami risk for northern California (or elsewhere). Nor do they likely have an affect upon the likelihood of a Cascadia subduction zone earthquake.

**UPDATE: 2016.01.29 20:00 PST
The USGS has prepared a moment tensor for the M 5.0 earthquake. I have updated the map. It is clear now that this is an extensional (normal) earthquake. I include an updated map below the original map.
/end update

    Here are the USGS web pages for these two earthquakes

  • 2016.01.30 M 5.0
  • 2016.01.30 M 4.9

Below is an interpretive map showing these two earthquakes as red circles, as well as other seismicity for the past week. I include an inset map of the Cascadia subduction zone (after Chaytor et al., 2004; Nelson et al., 2004), an inset map from Chaytor et al. (2004), and from Rollins and Stein (2010). I explain these inset maps below.

I include labels for the plate boundary fault systems in the region and include generic focal mechanisms for these fault systems. There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.

Based on the locations of these earthquakes, along with our knowledge of the local tectonics, I interpret the M 5.0 to possibly be a northeast striking left-lateral strike-slip fault earthquake. The M 4.9 could either be like that, or be an extensional earthquake (like the 2014.03.13 earthquake listed below). I summarized the regional tectonics of the Cascadia subduction zone recently here. The M 5.0 earthquake is similar to the earthquake “P” on the Rollins and Stein (2010) map.


**UPDATE: 2016.01.29 20:00 PST
Here is the updated map. Note the extensional moment tensor. This is aligned nicely with the ridges from the Gorda rise (which are visible in the large scale map at the bottom of this page.



/end update

There was an earthquake along the Gorda rise in 2014, much to the north of these two earthquakes. Here is my earthquake report for that 2014.03.13 M 5.2 earthquake.

Here is a map of the Cascadia subduction zone, modified from Nelson et al. (2006). The Juan de Fuca and Gorda plates subduct norteastwardly beneath the North America plate at rates ranging from 29- to 45-mm/yr. Sites where evidence of past earthquakes (paleoseismology) are denoted by white dots. Where there is also evidence for past CSZ tsunami, there are black dots. These paleoseismology sites are labeled (e.g. Humboldt Bay). Some submarine paleoseismology core sites are also shown as grey dots. The two main spreading ridges are not labeled, but the northern one is the Juan de Fuca ridge (where oceanic crust is formed for the Juan de Fuca plate) and the southern one is the Gorda rise (where the oceanic crust is formed for the Gorda plate).


Here is a map from Chaytor et al. (2004) that shows some details of the faulting in the region. The moment tensor (at the moment i write this) shows a north-south striking fault with a reverse or thrust faulting mechanism. While this region of faulting is dominated by strike slip faults (and most all prior earthquake moment tensors showed strike slip earthquakes), when strike slip faults bend, they can create compression (transpression) and extension (transtension). This transpressive or transtentional deformation may produce thrust/reverse earthquakes or normal fault earthquakes, respectively. The transverse ranges north of Los Angeles are an example of uplift/transpression due to the bend in the San Andreas fault in that region.


Here is a map from Rollins and Stein, showing their interpretations of different historic earthquakes in the region. This was published in response to the Januray 2010 Gorda plate earthquake. The faults are from Chaytor et al. (2004).


Here is a large scale map of the region for these two earthquakes. This is taken from Google Earth. The two largest orange circles (color represents depth < 33 km) are the M 5.0 and M 4.9, with diameter representing magnitude. The M 5.0 is clearly in the region where there are north-northeast striking faults.

I have Earthquake Reports for other CSZ related earthquakes here:

References:

  • Chaytor, J.D., Goldfinger, C., Dziak, R.P., Fox, C.G., 2004. Active deformation of the Gorda plate: Constraining deformation models with new geophysical data. Geology 32, 353-356.
  • Nelson, A.R., Kelsey, H.M., Witter, R.C., 2006. Great earthquakes of variable magnitude at the Cascadia subduction zone. Quaternary Research 65, 354-365.
  • Rollins, J.C., Stein, R.S., 2010. Coulomb Stress Interactions Among M ≥ 5.9 Earthquakes in the Gorda Deformation Zone and on the Mendocino Fault Zone, Cascadia Subduction Zone, and Northern San Andreas Fault. Journal of Geophysical Research 115, 19 pp.

Posted in cascadia, College Redwoods, earthquake, education, Extension, geology, gorda, HSU, humboldt, pacific, plate tectonics, strike-slip, Transform

Cascadia subduction zone: 316 years ago tonight!

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In commemoration of the last known Cascadia subduction zone earthquake, I present a summary background material here. Since last years commemoration, there have been a few additions.

Most notably was a pair of articles that were published in the New Yorker magazine, written by Kathryn Shulz. The first article summarized what we might expect from a CSZ earthquake and tsunami and the follow-up article discussed how to best prepare for this series of devastating events. The first article sparked a national debate after it was read by millions (using an estimate based upon the recorded time the website was being used). This debate has resulted in a renewed interest in becoming more resilient.

On this morning, 316 years ago, the Cascadia subduction zone fault ruptured as a margin wide earthquake. I here commemorate this birthday with some figures that are in two USGS open source professional papers. The Atwater et al. (2005) paper discusses how we came to the conclusion that this last full margin earthquake happened on January 26, 1700 at about 9 PM (there may have been other large magnitude earthquakes in Cascadia in the 19th century). The Goldfinger et al. (2012) paper discusses how we have concluded that the records from terrestrial paleoseismology are correlable and how we think that the margin may have ruptured in the past (rupture patch sizes and timing). The reference list is extensive and this is but a tiny snapshot of what we have learned about Cascadia subduction zone earthquakes. Brian Atwater and his colleagues have updated the Orphan Tsunami and produced a second edition available here for download and here for hard copy purchase (I have a hard copy).

Here is a map of the Cascadia subduction zone, modified from Nelson et al. (2006). The Juan de Fuca and Gorda plates subduct norteastwardly beneath the North America plate at rates ranging from 29- to 45-mm/yr. Sites where evidence of past earthquakes (paleoseismology) are denoted by white dots. Where there is also evidence for past CSZ tsunami, there are black dots. These paleoseismology sites are labeled (e.g. Humboldt Bay). Some submarine paleoseismology core sites are also shown as grey dots. The two main spreading ridges are not labeled, but the northern one is the Juan de Fuca ridge (where oceanic crust is formed for the Juan de Fuca plate) and the southern one is the Gorda rise (where the oceanic crust is formed for the Gorda plate).


IRIS and the US Geological Survey have recently produced an educational video about tectonic earthquakes in the region of the US Pacific Northwest. The project was funded by the National Science Foundation.

The Video


YT link for the embedded video below.
mp4 link for the embedded video below.

mp4 embedded video:

YT embedded video:

This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. We also can see how a subduction zone generates a tsunami. Atwater et al., 2005.

Here is a version of the CSZ cross section alone (Plafker, 1972).

Here is an animation produced by the folks at Cal Tech following the 2004 Sumatra-Andaman subduction zone earthquake. I have several posts about that earthquake here and here. One may learn more about this animation, as well as download this animation here.

This figure shows the regions that participate in this interseismic and coseismic deformation at Cascadia. Atwater et al., 2005. Black dots on the map show sites where evidence for coseismic subsidence has been found in coastal marshes, lakes, and estuaries.

This shows how the CSZ is deforming vertically today (Wang et al., 2003). The panel on the right shows the vertical motion in mm/yr.

This figure, also from Wang et al. (2003), shows their estimate of how the coseismic vertical motion may happen. Contours are in meters.

Here is a graphic showing the sediment-stratigraphic evidence of earthquakes in Cascadia. 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.

Here is a photo of the ghost forest, created from coseismic subsidence during the Jan. 26, 1700 Cascadia subduction zone earthquake. Atwater et al., 2005.

Here is a photo I took in Alaska, where there was a subduction zone earthquake in 1964. These tree snags were living trees prior to the earthquake and remain to remind us of the earthquake hazards along subduction zones.

This shows how a tsunami deposit may be preserved in the sediment stratigraphy following a subduction zone earthquake, like in Cascadia. Atwater et al., 2005. If there is a source of sediment to be transported by a tsunami, it will come along for the ride and possibly be deposited upon the pre-earthquake ground surface. Following the earthquake, tidal sediment is deposited above the tsunami transported sediment. Sometimes plants that were growing prior to the earthquake get entombed within the tsunami deposit.

The NOAA/NWS/Pacific Tsunami Warning Center has updated their animation of the simulation of the 1700 “Orphan Tsunami.”

Source: Nathan C. Becker, Ph.D. nathan.becker at noaa.gov


Below are some links and embedded videos.

  • Here is the yt link for the embedded video below.
  • Here is the mp4 link for the embedded video below. (2160p 145 mb mp4)
  • Here is the mp4 link for the embedded video below. (1080p 145 mb mp4)
  • Here is the text associated with this animation:

    Just before midnight on January 27, 1700 a tsunami struck the coasts of Japan without warning since no one in Japan felt the earthquake that must have caused it. Nearly 300 years later scientists and historians in Japan and the United States solved the mystery of what caused this “orphan tsunami” through careful analysis of historical records in Japan as well as oral histories of Native Americans, sediment deposits, and ghost forests of drowned trees in the Pacific Northwest of North America, a region also known as Cascadia. They learned that this geologically active region, the Cascadia Subduction Zone, not only hosts erupting volcanoes but also produces megathrust earthquakes capable of generating devastating, ocean-crossing tsunamis. By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater. That much motion over such a large area requires a very large earthquake to explain it—perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964. Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi) -long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o’clock at night in Cascadia on January 26, 1700 (05:00 January 27 UTC).

    The Pacific Tsunami Warning Center (PTWC) can create an animation of a historical tsunami like this one using the same too that they use for determining tsunami hazard in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they race around the globe one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).

    Toward the end of this simulated 24-hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” have a much higher impact than those to either side of it.

    This is the timeline of prehistoric earthquakes as preserved in sediment stratigraphy in Grays Harbor and Willapa Bay, Washington. Atwater et al., 2005. This timeline is based upon numerous radiocarbon age determinations for materials that died close to the time of the prehistoric earthquakes inferred from the sediment stratigraphy at locations along the Grays Harbor, Willapa Bay, and Columbia River estuary paleoseismic sites.

    Offshore, Goldfinger and others (from the 1960’s into the 21st Century, see references in Goldfinger et al., 2012) collected cores in the deep sea. These cores contain submarine landslide deposits (called turbidites). These turbidites are thought to have been deposited as a result of strong ground shaking from large magnitude earthquakes. Goldfinger et al. (2012) compile their research in the USGS professional paper. This map shows where the cores are located.

    Here is an example of how these “seismoturbidites” have been correlated. The correlations are the basis for the interpretation that these submarine landslides were triggered by Cascadia subduction zone earthquakes. This correlation figure demonstrates how well these turbidites have been correlated. Goldfinger et al., 2012

    This map shows the various possible prehistoric earthquake rupture regions (patches) for the past 10,000 years. Goldfinger et al., 2012. These rupture scenarios have been adopted by the USGS hazards team that determines the seismic hazards for the USA.

    Here is a plot showing the earthquakes in a linear timescale.


    I combined the plot above into another figure that includes all the recurrence intervals and segment lengths in a single figure. This is modified from Goldfinger et al. (2012).


Here is the Chaytor et al. (2004) map that shows their interpretation of the structural relations in the Gorda plate.

Here is a map from Rollins and Stein, showing their interpretations of different historic earthquakes in the region. This was published in response to the Januray 2010 Gorda plate earthquake. The faults are from Chaytor et al. (2004).

The Blanco fracture zone is also an active transform plate boundary. The BFZ is a strike slip fault system that connects two spreading ridges, the Gorda Rise and the Juan de Fuca Ridge. Here is a map that shows the tectonic setting and some earthquakes related to the BFZ from April 2015. There are some animations on this web page showing seismicity with time along the BFZ, over the past 15
years.

    References:

  • Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuju, Y., Eueda, K., and Yamaguchi, D.K., 2005. The Orphan Tsunami of 1700—Japanese Clues to a Parent Earthquake in North America, USGS Professional Paper 1707, USGS, Reston, VA, 144 pp.
  • Goldfinger, C., Nelson, C.H., Morey, A., Johnson, J.E., Gutierrez-Pastor, J., Eriksson, A.T., Karabanov, E., Patton, J., Gràcia, E., Enkin, R., Dallimore, A., Dunhill, G., and Vallier, T., 2012 a. Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper # 1661F. U.S. Geological Survey, Reston, VA, 184 pp.
  • McCrory, P.A., 2000, Upper plate contraction north of the migrating Mendocino triple junction, northern California: Implications for partitioning of strain: Tectonics, v. 19, p. 11441160.
  • McCrory, P. A., Blair, J. L., Oppenheimer, D. H., and Walter, S. R., 2006, Depth to the Juan de Fuca slab beneath the Cascadia subduction margin; a 3-D model for sorting earthquakes U. S. Geological Survey
  • Nelson, A.R., Kelsey, H.M., Witter, R.C., 2006. Great earthquakes of variable magnitude at the Cascadia subduction zone. Quaternary Research 65, 354-365.
  • Patton, J. R., Goldfinger, C., Morey, A. E., Romsos, C., Black, B., Djadjadihardja, Y., and Udrekh, 2013. Seismoturbidite record as preserved at core sites at the Cascadia and Sumatra–Andaman subduction zones, Nat. Hazards Earth Syst. Sci., 13, 833-867, doi:10.5194/nhess-13-833-2013, 2013.
  • Plafker, G., 1972. Alaskan earthquake of 1964 and Chilean earthquake of 1960: Implications for arc tectonics in Journal of Geophysical Research, v. 77, p. 901-925.
  • Wang, K., Wells, R., Mazzotti, S., Hyndman, R. D., and Sagiya, T., 2003, A revised dislocation model of interseismic deformation of the Cascadia subduction zone Journal of Geophysical Research, B, Solid Earth and Planets v. 108, no. 1.

Posted in cascadia, College Redwoods, education, geology, gorda, HSU, humboldt, Japan, pacific, plate tectonics, subduction, tsunami

Earthquake Report: Mediterranean!

20160125_gibraltar_interpretation_thumb

We just had a M 6.1 earthquake and a few aftershocks (M 4-5) in the western Mediterranean,

Here is the USGS website for this earthquake.

Here is a map showing the 5 largest earthquakes as circles.

There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.


For more on the graphical representation of moment tensors and focal mechnisms, check this IRIS video out:

Based on the mapping presented by Gracia et al (2012), Casciello et al. (2016), and the bathymetry, this earthquake may have ruptured one of the northeast striking structures that are shown in the lower left part of the Gracia et al. (2012) map. Therefore I interpret this earthquake to be a left-lateral strike-slip earthquake.

Here is a close up of Gracia et al. (2012) Figure 1. I provide their caption below in blockquote.


Figure 1. Schematic geological map of the Westernmost Mediterranean highlighting the position of the Alboran Domain enclosed between Iberia and northwest Africa. Its metamorphic rocks compose the floor of the western Alboran Sea and form the inner zones of the Betics and Rif mountain chains.

Here is the Casciello et al (2016) figure showing their tectonic interpretation. Figure is their map and Figure 2 is an earlier tectonic interpretation (Andrieux et al., 1971). I provide their caption below in blockquote.


Fig. 1. Regional topographic and bathymetric map of the southeast Iberian margin constructed from digital grids released by SRTM-3, IEO bathymetry (Ballesteros et al., 2008; Mu˜noz et al., 200Smilie: 8) and MEDIMAP multibeam compilation (MediMap et al., 200Smilie: 8) at  90m grid-size. Epicenters of the largest historical earthquakes (MSK Intensity>VIII) in the region are depicted by a white star (I.G.N., 2010). Grey arrows pointing opposite each other show the direction of convergence between the Eurasian and African plates from NUVEL1 model (DeMets et al., 2010). The black outlined rectangle depicts the study area presented in Fig. 2. BSF: Bajo Segura Fault; AMF: Alhama de Murcia Fault, PF: Palomares Fault, CF: Carboneras Fault, YF: Yusuf Fault, AR: Alboran Ridge. Inset: Plate tectonic setting and main geodynamic domains of the south Iberian margin along the boundary between the Eurasian and African Plates.

Fig. 3. Original model by Andrieux et al. (1971) to explain the formation of the Gibraltar Arc. The Alboran microplate would resist the eastward movement of the European and African plates, which are
forced by oceanic expansion in the Atlantic, causing the formation of the Betic-Rif chains.

Posted in College Redwoods, earthquake, education, europe, geology, HSU, plate tectonics, strike-slip, Transform

Earthquake Report: Alaska!

20160124_alaska_interpretation_thumb

Early this morning, we had a M 7.1 earthquake in the Cook Inlet of Alaska. Here is the USGS web page for this earthquake. Due to the magnitude and depth for this earthquake, there is no tsunami risk for CA/OR/WA.

Below is a map that shows the seismicity from the past 30 days, with circles colored for depth (see legend). In the lower right corner is a map produced by Dr. Peter Haeussler from the USGS Alaska Science Center (pheuslr at usgs.gov) that shows the historic earthquakes along the Aleutian-Alaska subduction zone. I also plot the slab contours, which are lines that represent the depth of the subduction zone fault. These were constructed using seismicity and other sources of information from Hayes et al. (2012). There is considerable uncertainty for these contours, but they are the best information that we have about the location of the subduction zone fault. I also include an inset of part of the USGS Open File Report 2010-1083-B (Benz at al., 2010).

There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal/Extensional, Thrust/Compressional, and Strike-Slip/Shear). There is more about moment tensors and focal mechanisms at the USGS.

This is an interesting earthquake. The depth (~128 km) aligns with the slab contours. This means that we could interpret this to be a subduction zone earthquake. Note how this earthquake is northwest of the 1964 Good Friday earthquake. This earthquake is down-dip from slip during that 27 March 1964 M 9.2 earthquake. I plot the epicenter on the Benz et al. (2010) map and the hypocenter along the cross section from Benz et al. (2010) as red circles. This earthquake occurred in the downgoing Pacific plate.


This is the visualized ground motion recorded in Homer, AK from the M7.1 Alaska earthquake on January 24, 2016. High pass filtered at 0.1Hz. Made with SeismoVisualize.

Here is a link to download the embedded video below (8 MB mp4).

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.


Here is a map that shows the regional extent of the 1964 earthquake. Regions of coseismic uplift/subsidence are delineated by blue/red polygons.

This animation shows the underlying causes of that earthquake, and tells how research done on the ground deformation contributed to confirmation of early theories of plate tectonics. More background material about this animation is found here. Here is a download link for the embedded video below (85 MB mp4).

Here is a large scale map (zoomed in) for the local scale, showing the main shock and the aftershocks. These aftershocks show an east-northeast trend.


Dr. Peter Haeussler produced a cross section for this region. Below is his description of this figure.


I made up a quick diagram (thanks Alaska Earthquake Center tools) showing the tectonic setting of the earthquake. This was a “Benioff zone” event, which means that the earthquake is related to bending of the subducting Pacific Plate as it slides into the mantle.

More interesting thoughts. Many earthquakes that are due to bending of the downgoing slab are in the upper part of the downgoing plate and these earthquakes are extensional due to the extension in the upper part of the plate due to the bending. Well, the opposite happens on the lower part of the bending plate. This is what happened during this M 7.1 earthquake, it is a compressional earthquake (in addition to the strike-slip part).

Here is a plot of static displacements for GPS sites as modeled by Jeff Freymueller at University of Alaska, Fairbanks (jeff.freymueller at gi.alaska.edu).


Here is the seismic record from Homer, AK. This was tweeted by Andy Frassetto at IRIS.


Here is an animation from Matt Gardine, showing ug PGA (500 = 0.5 PGA) measured at different locations.

I put together an animation of the seismicity for this region from the period of 1900-2016, for earthquakes of magnitude greater than or equal to M 6.5. Below is a map showing all these earthquakes and below that is the animation.


  • Here is a link to the embedded video below (25 MB mp4) .

Here is a video from Andrew Sayers:

Crazy earthquake in Kasilof

Posted by Andrew Sayers on Sunday, January 24, 2016

Here is a map that shows the seismicity (1960-2014) for this plate boundary. This is the spatial extent for the video below.

Here is a link to the file to save to your computer.

Here is a map showing the shaking intensity that uses the Modified Mercalli Intensity (MMI) scale. The MMI scale is a qualitative scale of the ground motions. There is more about the MMI here.


The USGS has prepared a fault slip model.


Today’s earthquake occurred near the inferred segment boundary between the locked Kodiak and creeping Kenai segments of the megathrust. Here is a map from Kelsey et al. (2015). They were looking at beach ridges on the Kenai penninsula, which are unrelated to this M 7.1 earthquake. I include the figure caption for part A, below as a blockquote.


A. Tectonic setting of the eastern Alaska-Aleutian subduction zone megathrust. Bold line delineates the surface trace of the megathrust, barbs on upper (North American) plate. Vertical deformation during the 1964 great Alaska earthquake depicted by two adjoining margin-parallel belts: a region of landward subsidence (blue) and a region of seaward uplift (red) (Plafker, 1969). Areas of highest slip occurred below the Prince William Sound and Kodiak segments, which are currently locked currently; while the intervening Kenai segment is creeping presently (Freymueller et al., 200Smilie: 8).

Based upon their work, they interpret that there may or may not be a segment boundary in this location (Kelsey et al., 2015).


Three alternatives for the tectonic context of the penultimate AD 1530-1840 Kenai earthquake in comparison to the AD 1964 earthquake and the third oldest earthquake. A. Coseismic uplift extent of the AD 1964 earthquake on which is superposed the inferred coseismic uplift extent of the AD 1788 rupture, if this historic earthquake involved rupture of the Kenai segment (alternative A). The colors show geodetic coupling ratio units as a fraction of the contemporary Pacific-North American plate rate, taken from Zweck et al., 2002. B. Alternative B (yellow) is the inferred uplift extent of the AD 1430-1650 subduction zone earthquake if this earthquake involved rupture of the Kenai segment. Alternative C (red) is the inferred uplift extent of the penultimate Kenai earthquake if earthquake rupture involved the Kenai segment alone. C. Inferred uplift extent for the ~900 cal yr BP earthquake, which is recorded in Prince William Sound, on the Kenai Peninsula (this study) as well as on Kodiak and Sitkinak Islands.

Here is more about the highway:

Video of the damage to approximately Mile 1 of K-Beach Road in Kasilof at about 10 am Sunday. The road has been reduced to one lane.

Posted by KSRM 920 AM on Sunday, January 24, 2016

Posted in alaska, College Redwoods, geology, HSU, plate tectonics, strike-slip, subduction

Cascadia Update: new tsunami simulation!

tsunami_cascadia_NOAA_NWS_PTWC_20160122

The NOAA/NWS/Pacific Tsunami Warning Center has updated their animation of the simulation of the 1700 “Orphan Tsunami.”

Source: Nathan C. Becker, Ph.D. nathan.becker at noaa.gov


    I provide some other background information about Cascadia here:

  • Cascadia’s 315th Anniversary 2015.01.26
  • Earthquake Information about the CSZ 2015.10.08

Below are some links and embedded videos.

  • Here is the yt link for the embedded video below.
  • Here is the mp4 link for the embedded video below. (2160p 145 mb mp4)
  • Here is the mp4 link for the embedded video below. (1080p 145 mb mp4)
  • Here is the text associated with this animation:

    Just before midnight on January 27, 1700 a tsunami struck the coasts of Japan without warning since no one in Japan felt the earthquake that must have caused it. Nearly 300 years later scientists and historians in Japan and the United States solved the mystery of what caused this “orphan tsunami” through careful analysis of historical records in Japan as well as oral histories of Native Americans, sediment deposits, and ghost forests of drowned trees in the Pacific Northwest of North America, a region also known as Cascadia. They learned that this geologically active region, the Cascadia Subduction Zone, not only hosts erupting volcanoes but also produces megathrust earthquakes capable of generating devastating, ocean-crossing tsunamis. By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater. That much motion over such a large area requires a very large earthquake to explain it—perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964. Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi) -long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o’clock at night in Cascadia on January 26, 1700 (05:00 January 27 UTC).

    The Pacific Tsunami Warning Center (PTWC) can create an animation of a historical tsunami like this one using the same too that they use for determining tsunami hazard in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they race around the globe one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).

    Toward the end of this simulated 24-hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” have a much higher impact than those to either side of it.

    Posted in cascadia, College Redwoods, education, geology, HSU, humboldt, pacific, tsunami