Earthquake Report: Ridgecrest Update #2

Well Well Well

Here is a commercial from Sony for Sony Discman following the 1995-96 Ridgecrest Earthquake (from which we have usurped this name for this July 2019 sequence).

The story continues to unfold.

  • Here is a graphic from the USGS that summarizes our observations as of 16 July.

Field Work Narrative

Last week I was lucky enough to spend a week in the field with my coworkers (California Geological Survey) and colleagues (U.S. Geological Survey) making observations of surface rupture from the Ridgecrest Earthquake Sequence (RES). It was initially termed the Searles Valley Earthquake Sequence, but we have since changed the name. Just check out #RidgecrestEarthquake on social media. Our work will be presented in several publications in the coming future. Stay tuned.

Many of us were granted rare access to the Naval Air Weapons Station China Lake. This emergency earthquake response effort was an unprecedented collaborative effort between the Navy, the CGS, and the USGS. We worked together as a team and accomplished our mission goals with due diligence. The CGS/USGS team is out in the field again this week, working off base. We plan to continue doing additional field work for weeks to come. (Though I need to get back to my tsunami stuff as we have deadlines to prepare new tsunami hazard products in the next few weeks to months.)

These collaborative efforts were based on a mutual respect between team agencies and team members. The field team members all appreciated the very special access we were granted. The commanding officer, Captain Paul Dale, is very supportive of scientific research and his support of our mission was evidence of this.

We were granted permission to take photos of the geologic evidence of the earthquake and ground shaking. We reviewed our images with the Public Affairs Officer to ensure that we did not take photos of any facilities or equipment that was on the base. This was important and we were very careful about this. We even double checked the images after we got back from the field.

I will add some photos to this page tomorrow.

Remote Sensing Narrative

There has also been a large number of Earth scientists using remote sensing data to evaluate the RES. These data are primarily from satellite images of different types (spectral imagery (another word for what we used to call air photos), RADAR, Global Positioning Systems (GPS), seismometer observations, etc.).

For most of these methods, pre-earthquake data are compared with post-earthquake data for a comparison. The methods used for these comparisons is advancing at a lightning pace. Every year, these models get better and better.

These remote sensing methods allow us to infer how the ground moved and slipped during and after the earthquake. We can get estimates of the slip on the fault from this type of analysis.

Combining different sources of remote sensing data also allows us to make estimates of the faults, where they moved, and how much they moved (in the subsurface).

I will present some of these observations below.

USGS Data Products

I prepared some interpretive posters for the M 7.1 earthquake shortly after it happened. The USGS earthquake pages are a source of great information as evidenced by how hard they are hit by web visitors following events as significant as the M 7.1. The website was unusable for periods of time. This demonstrates that the USGS is doing something right.

Last weekend, I spent Saturday preparing the same types of interpretive posters that I presented here, but as comparisons between the M 6.4 and M 7.1 temblors.

  • Here is an updated seismicity map. There are two main types of earthquakes on this map. I present this map both with aerial imagery and with a topographic (“hillshade”) basemap. I outline the general area of Ridgecrest in purple.
    1. First, there are an abundance of aftershocks aligned with the two main faults that ruptured during this sequence (the northwest trending M 7.1 fault and the northeast trending M 6.4 fault). Part of the northwest striking fault ruptured during the M 6.4 event.
    2. Second, there are several areas that show earthquakes that were triggered by this sequence. There are some triggered earthquakes along the Coso Range (where the Coso Geothermal Field is located), some events along the Garlock fault, and some temblors along the Ash Hill fault (in Panamint Valley, to the north of Searles Valley).

  • This is a seismicity comparison for the two earthquakes. on the left are earthquakes (USGS) from prior to the M 7.1 earthquake and on the right are quakes after and including the M 7.1 temblor. I plot the USGS Quaternary fault and fold database on the left as black lines.

  • Here is a map with landslide probability on it. Please head over to that report for more information about the USGS Ground Failure products (landslides and liquefaction). Basically, earthquakes shake the ground and this ground shaking can cause landslides. We can see that there is a low probability for landslides. However, we have already seen photographic evidence for landslides and the lower limit for earthquake triggered landslides is magnitude M 5.5 (from Keefer 1984-ish).

  • Here is a map showing liquefaction susceptibility. I explain more about this type of map in my original report for the M 6.4 earthquake. Scroll down a bit to find the landslide and liquefaction maps for that event.

  • Finally, here is a map that shows the shaking intensity for the M 6.4 and M 7.1 earthquakes. As I mention in my original report, this is based on a model that relates earthquake shaking intensity with earthquake magnitude and distance from the earthquake. Note that there was violent shaking from the M 7.1 event (MMI IX).

NASA JPL ARIA Data Products

  • NASA Jet Propulsion Laboratory (JPL) prepares Advanced Rapid Imaging and Analysis (ARIA) data products for major events worldwide. Their data are presented online here. I used the data from this event in a GIS computer program, but the data are prepared in Google Earth files too (so everyone can use them if they have a modern computer with an internet connection). This is a valuable government service.
  • This first map shows the results of modeling Synthetic Aperature Radar Interferometry data. Basically, Radar satellite imagery data from before and from after the earthquake are compared to model the amount of ground deformation that occurred between the satellite acquisitions. Each color band represents a certain amount of motion. This is referred to as the wrapped image.
  • Here are a series of sources of background information about InSAR analysis.

  • This map is made using the same basic data, though it has been processed in a way to show the overall ground motion with just two colors, instead of color bands. This is called the unwrapped image.

  • Below is the first in a series of videos that explains more about SAR and InSAR analyses.

Dr. Sotiris Valkaniotis

  • Dr. Valkaniotis is a Greek geologist who has a great set of remote sensing skills who studies earthquake geology and paleoseismology. I include lots of social media posts below where people share their analyses. However, I select two images from Dr. Valkaniotis for this earthquake. Contact him for more information about his processing. As embedded below in the social media section, here is the tweet that is the source of these two maps.
  • These images are similar to the NASA JPL ARIA unwrapped maps above. I include his description below in blockquote.

  • Gradient render from unwrapped LOS displacement map (higher quality 20m from SNAP). Surface ruptures (major & minor) are easily visible as dark linear features (high displacement gradient). Processing in @esa_gep. Descending pair from #Sentinel1, #Ridgecrestearthquake

    And the ascending pair from #Sentinel1, #Ridgecrestearthquake. Gradient render from unwrapped LOS displacement map (higher quality 20m from SNAP). Processing in @esa_gep.

  • Here is a map that Dr. Valkaniotis prepared showing fault lines he has interpreted from his model results.

  • Complex and detailed pattern of co-seismic ruptures for the #RidgecrestEarthquake sequence. Red lines are primary & secondary surface ruptures, together with small triggered ruptures away from main faults. Previously mapped Quaternary Faults with yellow, for comparison.

PBS News Hour: 2019.07.08

Death Valley at Devil’s Hole

The clip shows water violently sloshing around, rising and falling 10 to 15 feet, according to a park estimate. The video captures two angles, one looking into the cave and the other underwater inside it.

Devils Hole is a part of the desert uplands and spring-fed oases that make up the Ash Meadows complex, a national wildlife refuge.

Temblor Articles

Ross Stein (Ph.D.), Volkan Sevilgan (M.Sc.), Tiegan Hobbs (Ph.D.), Chris Rollins (Ph.D.), Geoffrey Ely, (Ph.D.), and Shinji Toda (Ph.D.) are coauthors to a suite of 5 articles presented on Temblor is a National Science Foundation funded organization that promotes earthquake insurance and seismic retrofits for people in earthquake country. I wrote several articles for Temblor prior to starting work at the California Geological Survey. (My efforts at are purely volunteer and do not reflect endorsement nor review from or by CGS.)

These reports are excellent sources of interpretive information at the detail for non experts (sometimes my reports are at a detail more aimed towards undergraduate geology students, though I attempt to make them available to a broad audience as well). I include a few figures from their reports that I find most interesting, but please check out their articles for more information!

  • Dr. Stein begins by presenting an hypothesis that these earthquakes are in a region of increased tectonic stress following the 1872 Owens Valley Earthquake, estimated to have a magnitude of M 7.6 (though it happened prior to modern seismometer instrumentation, so magnitude estimates have considerable uncertainty).
  • When earthquake faults slip, the surrounding crust is squished and squashed. This deformation changes the tectonic stresses in the crust. In some places this change causes an increase in the amount of stress on earthquake faults and in some places it decreases the tectonic stress. In places where the stress increases, the fault is brought closer to having an earthquake, and vice versa for places where the stress is diminished.
  • These stress changes are very small, so for a fault to be triggered by these changes in “static coulomb stress,” the fault had to be almost ready to slip before these changes happened. More can be found in Stein (2003) and Toda et al. (2005) linked below in the references.
  • In the map below, warm colors represent areas with an increase in (static coulomb stress) and cool colors represent a decrease in stress. I include their figure caption in blockquote below the figure (as for all their figures).

  • he site of the July 4th shock was likely brought closer to failure in the 1872 M~7.6 shock. Notice that the (red) stress trigger zones of the this 148-year-old quake are all seismically active today, whereas the (blue) stress shadows are generally devoid of shocks.

  • The Owens Valley fault triggering is speculative of course, since that earthquake was so long ago. However, there are other cases where aftershocks or triggered earthquakes are happening a long time after the main event. For example, there are ongoing aftershocks following an 1872 earthquake near Lake Chelan (Bakun et al., 2002; Brocher et al., 2018).
  • Stein and his colleagues calculated “static coulomb” stress changes imparted by the Ridgecrest Earthquake Sequence onto a series of other faults in the area. Read more about their analyses here.

  • Here we calculate stress transferred to the principal mapped faults, using the USGS slip model for the 7.1 and a model based on University of Nevada Reno GPS displacements for the 6.4 (not shown here for simplicity, but included). Most of the stress change is from the 7.1: it was several times larger than the 6.4 and torqued the surrounding crust far more. This fault inventory might be woefully incomplete, of course: the 7.1 itself struck on an unmapped fault. Nevertheless, the most striking result is the >2-bar stress increase on a 30-km (20-mile) section of the Garlock Fault. An end-to-end rupture on the Garlock, if (still) possible, would be in the magnitude 7.6-7.8 range.

  • In my interpretive posters above, I mention the areas where there have been triggered earthquakes (e.g. the Coso Geothermal Field, the Garlock fault, the Ash Hill fault). Turns out, Stein and his colleagues were thinking the same thing.
  • They prepared a figure in their report here where they show changes in “static coulomb” stress. They label the same areas I mention (except the Ash Hill fault in Panamint Valley). Take a look at the areas of increased stress compared to these three regions (even the Ash Hill fault is in an area of increased stress).

  • Faults in the red lobes are calculated to be brought closer to failure; those in the blue ‘stress shadows’ are inhibited from failure. The calculation estimates what the dominant fault orientations are around the earthquakes by interpolating between major mapped faults (shown in red lines). So, we would expect strong stressing in the Coso Volcanic Field to the north (where the aftershocks lie), and along the Garlock Fault to the south (but not where most of them lie).

  • Hobbs and Rollins speculate that the San Andreas fault may also have changes in (static coulomb) stress imparted by the Garlock fault if that were to slip. Read more in their article here.

  • If the western and central Garlock were to rupture, it would load the section of the San Andreas just north of Los Angeles. The jog in the San Andreas under the S in “Source” is at Palmdale. Figure from McAuliffe et al. [2013].

Below are all the Temblor articles to read

2019.07.04 Southern California M 6.4 earthquake stressed by two large historic ruptures
2019.07.05 Earthquake early warning system challenged by the largest SoCal shock in 20 years
2019.07.06 Magnitude 7.1 earthquake rips northwest from the M6.4 just 34 hours later
2019.07.06 M 7.1 SoCal earthquake triggers aftershocks up to 100 mi away: What’s next?
2019.07.09 The Ridgecrest earthquakes: Torn ground, nested foreshocks, Garlock shocks, and Temblor’s forecast
  • Here are the references for these Temblor articles.
    • Stein, R. S., and Sevilgen, V., (2019), Southern California M 6.4 earthquake stressed by two large historic ruptures, Temblor,
    • Hobbs, T.E. and Rollins, C., (2019), Earthquake early warning system challenged by the largest SoCal shock in 20 years, Temblor,
    • Ross S. Stein, Tiegan Hobbs, Chris Rollins, Geoffrey Ely, Volkan Sevilgen, and Shinji Toda, (2019), Magnitude 7.1 earthquake rips northwest from the M6.4 just 34 hours later, Temblor,
    • Ross S. Stein, Chris Rollins, Volkan Sevilgen, and Tiegan Hobbs, (2019), M 7.1 SoCal earthquake triggers aftershocks up to 100 mi away: What’s next?, Temblor,
    • Chris Rollins, Ross S. Stein, Guoqing Lin, and Deborah Kilb (2019), The Ridgecrest earthquakes: Torn ground, nested foreshocks, Garlock shocks, and Temblor’s forecast, Temblor,

Field Photos

  • Below are some field photos I took. I cannot tell anyone where they were taken (at least not yet) as we don’t have clearance. I may post more later, but wanted to post some to show people the type of observations we were making.
  • This is Dr. Chris DuRoss (USGS) as we walked across the scarp at our first site working together.

  • Here is a great one of Dr. Jessie T. Jobe (USGS, soon to be USBR) taking notes at that same scarp (DuRoss’ boots for scale).

  • This is a portion of a road where the fault crossed. There were several dm of lateral offset on either side of the road, but the road itself had an imperceptible amount of lateral offset (i.e. 1 ± 1 cm offset). There was some amount of compression here.

  • Here we were projecting the ground surface across the fault to estimate the amount of vertical displacement. Dr. Ryan Gold (USGS) is measuring while a Navy Base geologist is holding the profile stick along the ground surface.

  • Here is a photo very similar to Mr. Brian Olson’s tweeted photo, but I took this one instead. Dr. Belle Philibosian (USGS) is on the left and Kelly (NAWCL geologist) is on the right. This shows right-lateral strike-slip displacement of 420 cm. We thought nobody would believe us, so we made another measurement nearby to confirm.

  • I located some beautiful slickenlines (grooves in the fault surface created when the fault slips) and this is Dr. Beth Haddon (USGS) collecting strike, dip and rake data for these lines. We collected many photos of this site so that we can create a 3-D model (using structure from motion).

  • Here is Dr. Belle Philibosian looking spectacular as usual, providing scale to help us understand the amount of vertical separation across the fault in this location.

  • We located some evidence for liquefaction too. Here is a sand volcano, where lots of the sediment got washed away by the fluid that possibly shot up through this hole.

  • This was a great opportunity to show the compass orientation of these conjugate fault offsets in the road. The road material properties probably controlled the location of the faults here (there were pre-existing planes of weakness as evidenced by the tar patches, but some of the pavement faulting was new).


  • Amos, C.B., Bwonlee, S.J., Hood, D.H., Fisher, G.B., Bürgmann, R., Renne, P.R., and Jayko, A.S., 2013. Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California in GSA Bulletin, v. 125, no. 7-8,
  • Bakun, W.H., Ralph A. Haugerud, Margaret G. Hopper, Ruth S. Ludwin, 2002. The December 1872 Washington State Earthquake in BSSA, v. 92, no. 8.,
  • Brocher, T., Margaret G. Hopper, S.T. Ted Algermissen, David M. Perkins, Stanley R. Brockman, and Edouard P. Arnold, 2048. Aftershocks, Earthquake Effects, and the Location of the Large 14 December 1872 Earthquake near Entiat, Central Washington in BSSA, v. 108, no. 1.,
  • Frankel, K.L., Glazner, A.F., Kirby, E., Monastero, F.C., Strane, M.D., Oskin, M.E., Unruh, J.R., Walker, J.D., Anandakrishnan, S., Bartley, J.M., Coleman, D.S., Dolan, J.F., Finkel, R.C., Greene, D., Kylander-Clark, A., Morrero, S., Owen, L.A., and Phillips, F., 2008, Active tectonics of the eastern California shear zone, in Duebendorfer, E.M., and Smith, E.I., eds., Field Guide to Plutons, Volcanoes, Faults, Reefs, Dinosaurs, and Possible Glaciation in Selected Areas of Arizona, California, and Nevada: Geological Society of America Field Guide 11, p. 43–81, doi: 10.1130/2008.fl d011(03).
  • 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,
  • 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, , /li>
  • Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
  • Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, ,
  • 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,
  • McAuliffe, L. J., Dolan, J. F., Kirby, E., Rollins, C., Haravitch, B., Alm, S., & Rittenour, T. M., 2013. Paleoseismology of the southern Panamint Valley fault: Implications for regional earthquake occurrence and seismic hazard in southern California. Journal of Geophysical Research: Solid Earth, 118, 5126-5146,
  • 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.
  • 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,
  • Stein, R.S., Earthquake Conversations, Scientific American, vol. 288, 72-79, January issue, 2003. Republished in: Our Ever Changing Earth, Scientific American, Special Edition, v. 15 (2), 82-89, 2005.
  • Toda, S., Stein, R. S., Richards-Dinger, K. & Bozkurt, S. Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer. J. Geophys. Res. 110, B05S16 (2005)

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Category(s): earthquake, education, geology, plate tectonics, San Andreas, strike-slip

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