Toast, tsunamis, and the really big one | Chris Goldfinger | TEDxMtHood

Following an article in the New Yorker on July 20, 2015, the Cascadia subduction zone got more attention nationwide than it had ever seen previously. Most in the pacific northwest knew about Cascadia, but this article brought knowledge of the hazards to a national audience. A follow up article on July 28, 2015, the author Kathryn Shultz, wrote about how people can prepare for a CSZ earthquake and tsunami. Shultz was awarded a Pulitzer Prize for Feature Writing and a National Magazine Award for “The Really Big One,” recognition for her writing and the impact of this article.
On May 18, 2016, Dr. Chris Goldfinger presented a TEDx talk for TEDxMtHood. His talk was about the Cascadia subduction zone. This is a great talk for lay persons (most people). Here is Dr. Goldfinger’s OSU website. Here is Dr. Goldfinger’s earthquake blog.

    I provide more background information on the CSZ in several places.

  • Cascadia’s 315th Anniversary 2015.01.26
  • Earthquake Information about the CSZ 2015.10.08
  • Cascadia Paleoearthquakes 2012/03/11
    Here is what Dr. Goldfinger wrote to introduce his talk online.

  • I wondered why a crowd of New Yorkers would be interested in earthquakes. Several hundred gathered last October to hear a panel discuss “The Really Big One,” a New Yorker article about the Pacific Northwest that went viral after revealing to many what we geologists have known for a long time.
  • We were the warm-up acts for the “real stars” of the New Yorker Festival: Billy Joel, Norman Lear and the like… So I asked the crowd to imagine that someone came on the evening news one day and reported the discovery of a new, very large fault, a subduction zone that ran from Virginia to Newfoundland, generating magnitude 9 earthquakes on a regular basis, and would soon destroy New York.
  • Well, that exact scenario is not going to happen, but it did happen in the Northwest. It wasn’t a sudden thing, the news of this has been dribbling out over 30 years, so when the New Yorker article came out, I expected nothing to happen really.
  • But, instead, the story went viral and revealed something startling and new to the country, and even to a lot of Northwesterners – all of whom I was pretty sure had heard this information before. After all, it had been the subject of numerous documentaries, and tons of print and television news stories. And really, to west coast-centric me, the New Yorker was just a magazine with not-very-funny cartoons that piled up in dentists’ offices.
  • But what the article revealed was not not-new information, but rather that the story was not well known at all.
  • My inbox filled up with hundreds of emails from people all around the region, wondering if they would be “toast” living west of I-5, wondering if a tsunami would come up the Columbia to destroy Portland, and even wondering if one would come over the coast range and “get” Medford. Really, I’m not making this up. Not that we’re not in a tough spot: we are. But what is the reality?
  • The geologic records of previous earthquakes now stretches back ~ 10,000 years making Cascadia as we call it, the best-known fault on Earth. We can’t know when the next earthquake will come.
  • I think we’re collectively still blinking and hoping we heard something wrong. But the evidence is now about as airtight as it gets, so what to do? We have an opportunity to prepare for this and save lives. Will we learn from others and from the past and do it right?
  • This is what I’m going to talk about at TEDxMtHood this June: the seriousness of The Big One, and how we can all be prepared when it hits.
  • Here is a low angle oblique cross section of the CSZ.

    Here is a short bio for Dr. Goldfinger.

  • Dr. Chris Goldfinger is a marine geologist and geophysicist whose focus is on great earthquakes and the structure of subduction zones around the world. He is experienced using deep submersibles, multi-beam and side scan sonar, seismic reflection, and other marine geophysical tools all over the world. Recently, Chris was in the national spotlight after being featured in Kathryn Schulz’s article in The New Yorker, “The Really Big One.” His extensive research on the Cascadia subduction zone yielded an earthquake record extending through the Holocene epoch helping to develop a model of segmentation and earthquake recurrence. Conclusion: our area is overdue for a major earthquake.
  • Originally hailing from Palo Alto, Chris married a Salem girl and is currently Professor of Marine Geology at Oregon State University. His dad worked for NASA; so growing up in a house filled with stuff from the early probes like Voyager, Ranger, Surveyor, etc. made interest in earth sciences a natural progression. He is also into windsurfing, ocean sailing, and aerobatic flying.

Earthquake Report: Honey Lake fault zone

There was a swarm of seismic activity near Honey Lake a couple of days ago. I was stage managing at Reggae on the River, so missed the chance to write about this when it happened. Here is the USGS website for this M 4.5 earthquake.
Here is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
I also include the MMI contours from the M 5.1 earthquake near Lake Pillsbury. Here is my earthquake report for that M 5.1 earthquake. Compare the MMI contours for these two earthquakes. The Lake Pillsbury M 5.1 earthquake was ~19 km depth and the M 4.5 Honey Lake earthquake was ~7 km depth. Think about the factors that govern how strongly an earthquake is felt at the ground surface. Why does the M 4.5 earthquake, the smaller magnitude earthquake, have larger ground motions at Earth’s surface?
I plot the moment tensor for this earthquake and I interpret this earthquake to be a northwest striking right lateral strike-slip earthquake. This is based upon the mapped faults in the region and their sense of motion, which is synthetic to the San Andreas fault system to the west. I used this kml to make this map.
The San Andreas fault is a right-lateral strike-slip transform plate boundary between the Pacific and North America plates. The plate boundary is composed of faults that are parallel to sub-parallel to the SAF and extend from the west coast of CA to the Wasatch fault (WF) system in central Utah (the WF runs through Salt Lake City and is expressed by the mountain range on the east side of the basin that Salt Lake City is built within). There was a recent earthquake between the San Andreas and Maacama faults in August of 2016 and an earthquake series along the Bartlett Springs fault system on 2016.08.10. The three main faults in the region north of San Francisco are the SAF, the MF, and the Bartlett Springs fault (BSF). The SAF, MF, and BSF are all right lateral strike-slip fault systems.
The major strike slip fault systems that extend along the east side of the Sierra Nevada mountains include the Eastern California Shear Zone (ECSZ, in the south) and the Walker Lane (WL, in the north). The Honey Lake fault system is part of the northern terminus of the Walker Lane and may eventually reveal how Pacific/North America relative plate motion extends westward to the Pacific plate. The ECSZ and WL delineate the eastern boundary of the Sierra microplate.

    I include inset maps, from upper left, clockwise.

  • I placed a moment tensor / focal mechanism legend in the upper right corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. Based upon the proximity to the Honey Lake fault system, I interpret the M 4.5 earthquake as a right-lateral strike-slip earthquake.
  • I include a map from Hunter et al. (2011) that shows the plate boundary scale tectonics and an inset with details of active faulting in the region. This map shows the Mohawk Valley fault zone that is also highlighted in the interpretive map below.
  • I include a map from Gold et al. (2014) that also shows the regional active faults related to the Walker Lane.
  • I include a map from Turner et al. (2008 ) that show some faults in the region that were evaluated for slip rates by the authors. These authors examined the slip rate and paleoseismic history by evaluating an offset natural stream bank. They interpret at least four surface-rupturing earthquakes during the past 7025 calendar years. Interevent times range from 730 to 990 years. They calculate a minimum slip rate for the Honey Lake fault of 1.7 ± 0.6 mm/yr.
  • I include a map that shows the epicenters from the last 30 days in relation to Honey Lake and the faults that are included in the USGS Active Fault and Fold Database.


    These are the USGS websites for the larger magnitude earthquakes plotted in the map above.

  • 2016.08.04 M 4.5 04:55:35 UTC
  • 2016.08.04 M 4.0 04:58:32 UTC
  • 2016.08.04 M 2.8 05:11:34 UTC
  • 2016.08.04 M 2.5 05:45:07 UTC
  • 2016.08.04 M 2.2 06:40:07 UTC
  • 2016.08.04 M 3.3 10:13:52 UTC
  • 2016.08.04 M 2.0 15:55:23 UTC
    Below are the two attenuation with distance plots for the M 5.1 and M 4.5 earthquakes plotted in my interpretive poster above. These show how the ground motions attenuate (get absorbed and diminish) with distance from the earthquake.

  • The M 4.5 earthquake (6.9 km depth).

  • The M 5.1 earthquake.

    Here is the Hunter et al. (2011) map. I include the figure caption as a blockquote below.

    (a) Generalized location map showing the Walker Lane–eastern California shear zone (ECSZ) in relation to the Basin and Range Province, the Sierra Nevada microplate, and the San Andreas fault system, as well as relative motions and rates. (b) Generalized fault map of the northern Walker Lane: PF, Polaris fault; DVFZ, Dog Valley fault zone; MVFZ, Mohawk Valley fault zone; GVF, Grizzly Valley fault; HLF, Honey Lake fault; WSF, Warm Springs Valley fault; PLF, Pyramid Lake fault; OF, Olinghouse fault; and CL, Carson lineament. Barbed arrows show relative motion of strike-slip faults, and black dots shows down-thrown side of normal faults. Parts (a) and (b) are modified from Faulds and Henry (2008 ).

    Here is the Gold et al. (2014) map. I include the figure caption as a blockquote below.

    Map of the northern Walker Lane study area and regional strike-slip and normal faults, simplified from the U.S. Geological Survey, Nevada Bureau of Mines and Geology, and California Geological Survey [2006], Faulds and Henry [2008], the California Department of Water Resources [1963], Saucedo and Wagner [1992], Hunter et al. [2011], Gold et al. [2013a, 2013b], Olig et al. [2005], and our mapping using lidar data and field observations. Abbreviations: CL, Carson Lineament; DVF, Dog Valley fault; ETFZ, East Truckee fault zone; GVF, Grizzly Valley fault; HLF, Honey Lake fault; HSF, Hot Springs fault; IVF, Indian Valley fault; MVFZ, Mohawk Valley fault zone; OF, Olinghouse fault; PF, Polaris fault; PLF, Pyramid Lake fault; and WSVF, Warm Springs Valley fault. Arrows indicate relative direction of strike-slip fault movement. Bar and ball indicates downthrown block of normal faults. Star depicts location of Sulphur Creek site.

    Here is the Turner et al. (2008 ) map. I include the figure caption as a blockquote below.

    Location of (a) the northern Walker Lane (shaded gray) with respect to the Pacific plate (denoted PP), the San Andreas fault (denoted SA), the North American plate (denoted NAP), the Sierra Nevada, and the Basin and Range province. Plate velocity (∼50 mm=yr) is for the Pacific plate relative to stable North America. Measured geodetically, the Northern Walker Lane is accumulating about 6  2 m=yr of relative right-lateral motion. (b) The Honey Lake fault zone. Strike-slip faults are black and normal faults are white. The Honey Lake (denoted HL), Pyramid Lake (denoted PL), and Winnemucca Lake (denoted WL) subbasins of Lake Lahontan and Lake Tahoe (denoted LT) are labeled. Faults are simplified and generalized from the USGS (2006), and shaded relief generated from 3′ SRTM data are courtesy of NASA/ NGA/USGS.

    There was a M 3.8 earthquake along Lake Almanor in March of 2015, near a swarm from 2013 (with an earthquake of M = 5.7). Here is my earthquake report for that swarm. This seismicity is probably related to the Indian Valley fault. The Indian Valley fault is at the northern end of the Mohawk Valley fault system. We will be taking a look at this fault system (and the sedimentary/stratigraphic history) for the 2015 Pacific Cell Friends of the Pleistocene field trip. The Mohawk Valley fault system is probably the northern extension of the Walker Lane. The Walker Lane is the northernmost extension of the east-of-the-Sierra-Nevada-mtns part of the plate boundary between the North America and Pacific plates (the most well known part of this plate boundary is the San Andreas fault). We looked at the Walker Lane for the 2010 Pacific Cell Friends of the Pleistocene field trip. We looked at faulting in the Lake Tahoe region for the 2012 Pacific Cell Friends of the Pleistocene field trip.
    Here is a map showing the swarm from 2013, as well as the location of today’s M 3.8 earthquake. All orange dots represent earthquake epicenters from the year of 2013. On the map I have placed the moment tensors for the M 5.7 and M 3.8 earthquakes. The Indian Valley fault is shown in orange. I extended this fault (as a red dashed line) to where it may exist, based upon the recent seismicity. All the other lines are from the USGS fault and fold database. Anyone can use these fault data and they are downloadable here.
    As Tom Sawyer of Piedmont Geosciences stated, “Yes, the Lake Almanor basin is a pull apart basin resulting from a releasing bend between the northern Mohawk Valley-Indian Valley fault system and the southern Hat Creek graben. See 1995 Pacific Cell FOP guidebook for more details.” More can be found on Sawyer’s page here.

Earthquake Report: Bartlett Springs fault system, Lake Pillsbury

We just had a good sized earthquake adjacent to the mapped surface trace of the Bartlett Springs fault, southeast of Lake Pillsbury. Here is the USGS website for the M 5.1 earthquake.
Here is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. See the attenuation plot versus distance below to compare the difference between this model estimate and the real observations. The fit is pretty good.
I plot the moment tensor for this earthquake and I interpret this earthquake to be a northwest striking right lateral strike-slip earthquake. This is based upon the mapped faults in the region and their sense of motion, which is synthetic to the San Andreas fault system to the west. I used this kml to make this map.
The San Andreas fault is a right-lateral strike-slip transform plate boundary between the Pacific and North America plates. The plate boundary is composed of faults that are parallel to sub-parallel to the SAF and extend from the west coast of CA to the Wasatch fault (WF) system in central Utah (the WF runs through Salt Lake City and is expressed by the mountain range on the east side of the basin that Salt Lake City is built within). There was a recent earthquake between the San Andreas and Maacama faults in August of 2016. The three main faults in the region north of San Francisco are the SAF, the MF, and the Bartlett Springs fault (BSF). The SAF, MF, and BSF are all right lateral strike-slip fault systems. Without more seismicity or mapped faults to suggest otherwise, this is a reasonable interpretation.

    I include some insets in the map below:

  • In the upper right corner, I place a map shows the configuration of faults in central (San Francisco) and northern (Point Delgada – Punta Gorda) CA (Wallace, 1990).
  • To the left of that, 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.
  • In the lower right corner I include one version of the Did You Feel It? map. This is the result of people submitting their observations on the USGS website.
  • In the lower left corner, I include a map that shows the major fault systems in this region (McLaughlin et al., 2012). In their 2012 publication, McLaughlin et al. present their interpretations for the evolution of the Rogers Creek-Maacama right-lateral fault system, the SAF plate boundary fault system to the west of the Bartlett Springs fault system.



This map shows today’s seismicity as red and orange circles. Faults are mapped as red lines and compare with the map above to note that from left to right (west to east) are the SAF, MF, and BSF. Fort Bragg is located in the northwest part of the map and Sacramento is in the southeast part of the map.


This plot shows how the ground motions decay with distance from the earthquake. The blue dots show the survey results and the orange line shows how a computer simulation based attenuation model suggests that the ground motions would reduce with distance from the earthquake. The orange dots show the median data for each data bin. Note how well the observations fit the attenuation (i.e. Ground Motion Prediction Equation) models.


This is my interpretive map for the earthquake from August 8, 2015. Compare the MMI contours with the interpretive map for today’s M 5.1 earthquake. These maps are at a similar scale.


I created an animation that shows the seismicity of this region from 1960 through Sunday, 2015.08.30. While this animation was made for a different earthquake (from 2015), it still reveals where the historic seismicity is located. Note how there is little recent historic seismicity in the region of today’s M 5.1earthquake. This is the USGS query that I used to create the animation, in the form of a kml file. Here is a static map that shows all earthquakes for this region.


Here is the animation. Either download the file here or click on the animation below.


Here is the (Wallace, 1990) map. I include the figure caption as a blockquote below. Below the citation is this map presented on its own.

Geologic sketch map of the northern Coast Ranges, central California, showing faults with Quaternary activity and basin deposits in northern section of the San Andreas fault system. Fault patterns are generalized, and only major faults are shown. Several Quaternary basins are fault bounded and aligned parallel to strike-slip faults, a relation most apparent along the Hayward-Rodgers Creek-Maacama fault trend.

Here is a map that shows some slip rates for the faults that make up the Pacific-North America plate boundary system (Wallace, 1990). I include the figure caption as a blockquote below. Below the citation is this map presented on its own.



Sketch map of western and southwestern California, showing selected major faults exhibiting evidence of Quaternary activity in the San Andreas fault system. Average Quaternary slip rates are based on measured values from published sources and, where measurements are incomplete or unavailable, on interpreted geologic and geomorphic evidence. Slip components on northwest-trending faults are predominantly horizontal, right lateral, and consistent with North American-Pacific plate motion Group of east-west-trending faults between lat 34°00′ and 35°30′ N. exhibit a more complex slip pattern, including chiefly reverse faulting but also some strike slip. Areas above 600-m elevation (colored) exhibit evidence of late Cenozoic uplift and enclose most areas of Quaternary uplift, but elevation pattern reveals no such major local uplifts as those near Ventura (approx 1 cm/yr) and along the Newport-Inglewood fault zone (NI). Faults dotted where concealed by water.

About 75% of the relative plate motion is accommodated along the SAF and its synthetic sister faults in the northern CA region. The rest of the plate boundary motion is accommodated along the Eastern CA shear zone and Walker Lane, along with the Central Nevada Seismic Belt, and the Wasatch fault systems. In Northern CA, there is about 33-37 mm/yr strain accumulated on the SAF plate boundary system. About 18-25 mm/yr is on the SAF, 8-11 mm/yr on the MF, and 5-7 mm/yr on the Bartlett Springs fault system (Geist and Andrews, 2000).

    Here is a map from McLaughlin et al. (2012) that shows the regional faulting. I include the figure caption as a blockquote below.

    Maps showing the regional setting of the Rodgers Creek–Maacama fault system and the San Andreas fault in northern California. (A) The Maacama (MAFZ) and Rodgers Creek (RCFZ) fault zones and related faults (dark red) are compared to the San Andreas fault, former and present positions of the Mendocino Fracture Zone (MFZ; light red, offshore), and other structural features of northern California. Other faults east of the San Andreas fault that are part of the wide transform margin are collectively referred to as the East Bay fault system and include the Hayward and proto-Hayward fault zones (green) and the Calaveras (CF), Bartlett Springs, and several other faults (teal). Fold axes (dark blue) delineate features associated with compression along the northern and eastern sides of the Coast Ranges. Dashed brown line marks inferred location of the buried tip of an east-directed tectonic wedge system along the boundary between the Coast Ranges and Great Valley (Wentworth et al., 1984; Wentworth and Zoback, 1990). Dotted purple line shows the underthrust south edge of the Gorda–Juan de Fuca plate, based on gravity and aeromagnetic data (Jachens and Griscom, 1983). Late Cenozoic volcanic rocks are shown in pink; structural basins associated with strike-slip faulting and Sacramento Valley are shown in yellow. Motions of major fault blocks and plates relative to fi xed North America, from global positioning system and paleomagnetic studies (Argus and Gordon, 2001; Wells and Simpson, 2001; U.S. Geological Survey, 2010), shown with thick black arrows; circled numbers denote rate (in mm/yr). Restraining bend segment of the northern San Andreas fault is shown in orange; releasing bend segment is in light blue. Additional abbreviations: BMV—Burdell Mountain Volcanics; QSV—Quien Sabe Volcanics. (B) Simplifi ed map of color-coded faults in A, delineating the principal fault systems and zones referred to in this paper.

    Here is a map that shows the shaking potential for earthquakes in CA. This comes from the state of California here. I include the figure caption as a blockquote below.

    Earthquake shaking hazards are calculated by projecting earthquake rates based on earthquake history and fault slip rates, the same data used for calculating earthquake probabilities. New fault parameters have been developed for these calculations and are included in the report of the Working Group on California Earthquake Probabilities. Calculations of earthquake shaking hazard for California are part of a cooperative project between USGS and CGS, and are part of the National Seismic Hazard Maps. CGS Map Sheet 48 (revised 2008) shows potential seismic shaking based on National Seismic Hazard Map calculations plus amplification of seismic shaking due to the near surface soils.

      References

    • Geist, E.L. and Andrews D.J., 2000. Slip rates on San Francisco Bay area faults from anelastic deformation of the continental lithosphere, Journal of Geophysical Research, v. 105, no. B11, p. 25,543-25,552.
    • McLaughlin, R.J., Sarna-Wojcicki, A.M., Wagner, D.L., Fleck, R.J., Langenheim, V.E., Jachens, R.C., Clahan, K., and Allen, J.R., 2012. Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California in Geosphere, v. 8, no. 2., p. 342-373.
    • Wallace, Robert E., ed., 1990, The San Andreas fault system, California: U.S. Geological Survey Professional Paper 1515, 283 p. [http://pubs.usgs.gov/pp/1988/1434/].