I have reviewed a small portion of the literature for the tectonics of the northern Eastern California shear zone, Owens Valley fault, Garlock fault, etc. I have a basic knowledge of this region and have attended several Pacific Cell Friends of the Pleistocene field trips in this area, but have not done extensive literature review for this area (though I did help Steve Bacon (DRI PhD. student defending soon) for his work on the Owens Valley fault for his M.S. thesis at Humboldt State University, Dept. of Geology, while I was a graduate student there with “early morning” Steve).
Below I present some key overview figures from some of the papers I reviewed today. See the reference list for additional papers. However, first I present a new map.
- In review, here are my previous Earthquake Reports
The original Earthquake Report for this widely felt sequence is here.
The update #1 Earthquake Report for this widely felt sequence is here.
The update #2 Earthquake Report for this widely felt sequence is here.
The update #3 Earthquake Report for this widely felt sequence is here.
Global Strain Rate Map
- Strain is basically the change in shape or volume of a material through time. The Earth deforms with space and time in relation to geospatial variations in plate tectonic motions.
- Tectonic strain can be measured in a variety of methods. Most people are familiar with geodetic methods. Geodesy is the study of the motion of the Earth as measured at discrete locations (e.g. with GPS observations). One may use changes in position at GPS sites to measure how the Earth moves, so we can directly measure changes in shape this way.
- Geodetic data can be combined with geologic and seismicity data to evaluate tectonic strain at global, regional, and local scales.
- In 1998 the International Lithosphere Program started compiling a global dataset to support the construction of a Global Strain Rate Map (GSRM; Kreemer et al., 2000, 2002, 2003, 2014).
- The GSRM has been incorporated into the Global Earthquake Model of Seismic Hazard, v 2.1 presented online here.
- I present a map for the Ridgecrest Earthquake Sequence that uses an older version of the GSRM (v 1.2). The color ramp is based on the “second invariant” of strain. Warmer colors show regions of greater tectonic strain. Units are in 10 per year. I acquired these data here.
Geologic Map
- There are some larger scale geology maps for this region, but they cost money (Dibblee Foundation/AAPG). Needless to say, I don’t have the $50 to buy them right now. They are geotiffs, so would overlay nicely.
- The map below shows seismicity for the past month overlain upon the 1962 California Division of Mines and Geology 1:250,000 scale geologic map (Jennings et al., 1962). I prepared this on 21 July 2019 after georeferencing the map from the CGS website..
UNAVCO Response Page
- UNAVCO has event response pages where people post visualizations of data. Here is the Ridgecrest Earhquake Response Page.
OTA-measured GNSS static displacements from the real-time GNSS system (blue) compared to the seismically derived static displacements (pink).

Preliminary coseismic horizontal vector displacements for the July 4, 2019 M 6.4 earthquake. The 5-minute sample rate time series were obtained using rapid orbits from the Jet Propulsion Laboratory.

Ultra rapid analysis coseismic offsets calculated by the Nevada Geodetic Laboratory (NGL) for a subset of continuous GPS stations in the region of the July 6, 2019 M 7.1 earthquake.

Rapid analysis coseismic offset pattern for the July 6, 2019 M 7.1 Ridgecrest earthquake, from the Nevada Geodetic Laboratory (NGL)

GPS derived coseismic displacements of Mw6.4 foreshock. Five days of GPS data spanning the foreshock and prior to the mainshock were processed to obtain the solution.

GPS derived coseismic displacements of Mw7.1 mainshock. Four days of GPS data spanning the mainshock and after the foreshock were processed to obtain the solution.

Preliminary slip results derived from geodetic and seismic data for the July 6, 2019 M 7.1 Ridgecrest earthquake, from the Pacfic Northwest Seismic Network. The slip model was run through G-FAST.
- Here is a video showing real time GPS displacement from 1Hz GPS/GNSS NOTA data analyzed by Christine Puskas.
Background Literature – Tectonics
- Here is a great overview map of the faults in the region from Oskin et al. (2008). Their paper is about their research to quantify the tectonic loading of faults in the Eastern California shear zone. Note that they use about 12 mm per year of Pacific-North America relative plate motion across this region.
A: Index map of southwest North America showing geodetic provinces from Bennett et al. (2003) and location of Mojave block. Velocities of geodetically stable regions are shown relative to Colorado Plateau. ECSZ—eastern California shear zone in Mojave block. Shear zone continues northward into western Great Basin province. GF—Garlock fault. B: Index map of the Mojave block with active faults and locations of recent earthquake ruptures. Circles show localities of slip-rate measurements that sum to ≤6.2 ± 1.9 mm/yr across the ECSZ. GPS—global positioning system.
- Here is another good overview map, showing the faults for which Petersen and Wesnousky (1994) reviewed slip rates in that publication. They present an excellent review of all slip rate and paleoseismic investigations at the time that paper was published.
Map showing sites of slip rate studies in southern California for the San Andreas (SAI-14), San Jacinto (SJI-13), Elsinore-Whittier (El-8), Newport- Inglewood (N1-3), Palos Verdes (N4-6), Rose Canyon (N7), Transverse Ranges (T1-50), Mojave (MI-6), and Garlock (G1-9) faults.
- Oskin and Iriondo studied the Blackwater fault, the right-lateral strike-slip fault system that extends from the south into the region of the Ridgecrest Earthquake Sequence. The Blackwater fault is connected to the south with the Calico fault (a fault between the 1992 and 1999 earthquakes). This appears to be the major Eastern California Shear zone fault that extends towards the Airport Valley and Little Lake faults (which ruptured during the Ridgecrest Earthquake Sequence).
A: Index map of Pacific–North America plate boundary through southwest North America. Principal faults are shown as thick black lines. Tectonically stable areas are outlined by dotted lines. Walker Lane and Eastern California shear zone, shown as dark gray band encompassing network of active faults, together absorb 9%–23% of total plate boundary shear (Dixon et al., 2000; Dokka and Travis, 1990a). JDF—Juan de Fuca; MTJ— Mendocino triple junction. B: Index map of Eastern California shear zone showing fault slip rates (in parentheses, mm/yr) determined by paleoseismic studies (Klinger and Piety, 2000; Lee et al., 2001; McGill and Sieh, 1993; Rockwell et al., 2000; Zhang et al., 1990). Heavy dark gray lines outline historic earthquake ruptures (Beanland and Clark, 1994; Sieh et al., 1993; Treiman et al., 2002). Heavy, medium gray band highlights Blackwater–Calico fault system. Light gray band surrounding Blackwater fault and passing north of Garlock fault is zone of localized 1.2 6 0.5 mm/yr strain accumulation documented by radar interferometry (Peltzer et al., 2001). C: Neotectonic map of Blackwater fault, showing type and orientation of fault line scarps with ticks on downthrown side. Dark patterned areas are lava flows cut by Blackwater fault (Dibblee, 1968, 1967; Smith, 1964)
- Peltzer et al. (2001) evaluate the amount of tectonic strain that has accumulated over time (see geodesy section to learn more about strain). First I present their tectonic map.
Tectonic map of southern California. Solid lines are active faults (Jennings, 1975). Yellow dots are relocated earthquakes between 1981 and 2000 (Hauksson, 2000). Dashed-line box is area covered by Earth Resource Satellite (ERS) data used in this study. White dashed line shows location of concentrated shear observed in synthetic aperture radar (SAR) data. Black stars indicate epicenters of recent earthquakes: OV—1872 Owens Valley, JT—1992 Joshua Tree, L—1992 Landers, BB—1992 Big Bear, N—1994 Northridge, RC—1994 and 1995 Ridgecrest, HM—1999 Hector Mine. Heavy solid lines depict surface ruptures of Landers (Sieh et al., 1993), Hector Mine (U.S. Geological Survey and California Division of Mines and
Geology, 2000; Peltzer et al., 2001), and Owens Valley (Beanland and Clark, 1994; only southern half of rupture is shown) earthquakes. Black dots and arrows show locations and observed velocities of 11 stations of Yucca GPS array (Gan et al., 2000).
* Faults are listed in the paper
- Guest et al. (2003) used geologic mapping and geochronologic data (ages of geologic units) to constrain a tectonic model. They suggest that some of the faults in the region developed as a result of tectonic blocks rotating about a vertical axis. First we see their geologic map.
Segment of Trona sheet geologic map showing Owlshead block, southern Death Valley, and Northeast Mojave block. WWFZ— Wingate Wash fault zone, BMF—Brown Mountain fault, OLF—Owl Lake fault, DVFZ—Death Valley fault zone, MSS—Mule Springs strand, LLS—Leach Lake strand, DWLF—Drink Water Lake fault, FIF—Fort Irwin fault, CCF—Coyote Canyon fault, TMF—Tiefort
Mountain fault.
- Here is the Guest et al. (2003) map showing their interpretation of how these faults developed over time.
In this model the Owlshead and southern Panamint blocks are hypothesized to have undergone sinistral transtension in response to a clockwise rotation of their southern confining boundary (Garlock fault zone).
RTR—Radio Tower Range, SOM—Southern Owlshead Mountains, WWFZ—WingateWash fault zone, BMF—Brown Mountain fault, OLF—Owl Lake fault, GF—Garlock fault, MSS—Mule Springs strand, LLZ—Leach Lake fault zone, SDVFZ—Southern Death Valley fault zone.
Background Literature – Geodesy
- Gan et al. (2003) present a summary of geodetic data where they show that the Owens Valley, Little Lake, and Helendale faults form the generalized western boundary of the Eastern California shear zone (there are additional right-lateral faults to the west however).
Map showing the location of the ECSZ, the GPS arrays, the station velocities (relative to the fixed North America), and the principal faults in southern California (from Jennings [1992]). The thick dashed lines directed N23°W show the boundaries of the assumed parallel-sided ECSZ. The thin dashed lines extended from the segments of the Garlock fault show the trends of the segments.
- One of the challenges with interpreting geodetic data is comparing earthquake fault slip rates inferred from geodetic methods with rates calculated using geologic data (either from long term offsets of bedrock, or from more recent rates using fault trenches).
- Chuang and Johnson (2011) present their comparisons of GPS slip rates with geologic rates.
- Blue = geologic rate
- Black = geodetic rate
- Magenta = block model rate from their analyses
Comparison of geologic fault slip rates (blue, mm/yr) used in model, range of estimates from elastic block models (black) of Becker et al. (2005) and Meade and Hager (2005), and estimates from our block model (magenta) along major faults. Negative is left lateral. Light red lines are surface fault traces, and white thick lines are model blocks. Blue arrows are Southern California Earthquake Center (SCEC) crustal motion map 3 (Shen et al., 2003) velocities with respect to stable North America.
*See their paper for fault abbreviations.
- Here is an interesting figure showing their (Chuang and Johnson, 2011) estimate of the relative position in the earthquake cycle for these faults. This is based on published recurrence intervals for these faults (the average time between earthquakes given paleoseismic investigation data).
Summary of assumed geologic rates, recurrence interval (T), and time since last earthquake (teq) in Southern California. (For further discussion of sources of T and teq, see footnote 1). Blue numbers are expert opinion slip rates from Working Group on California Earthquake Probabilities (2008) and red numbers are rates from other paleoseismology data.
Color of rupture segment represents ratio of time since last earthquake and recurrence interval. Hot (red) colors show segments are in early earthquake cycle, and cold (blue) colors show late earthquake cycle.
- This is the summary of the Chuang and Johnson (2011) slip rate comparison.
A: Geologic fault slip rates versus slip rates inferred from geodetic data. Geologic rates are summarized in Table DR1 (see footnote 1). Blue bars are slip rate comparisons from Meade and Hager (2005) and red bars are from this study. B: Normalized velocity across Garlock fault (blue), Mojave segment of San Andreas fault (red), and eastern California shear zone (ECSZ, green) from our cycle model. Black line is normalized velocity derived from elastic model.
- Here is an earlier analysis comparing geodetic rates with geologic rates (Dixon et al., 2003). First we see a map showing the faults from which the fault comparisons are shown.
Sketch map of study area, modified from Dixon et al. (1995). Bar marks approximate location of Global Positioning System transect (Gan et al., 2000). GF— Garlock fault. Labeled faults of Eastern California shear zone: ALF— Airport Lake fault zone; OVF—Owens Valley fault zone; HMF—Hunter Mountain–Panamint Valley fault zone; DVF— Death Valley–Furnace
Creek fault zone; FLV— Fish Lake Valley fault zone.
- Here is the east west profile from Dixon et al. (2003). The horizontal axis is distance and the vertical axis is the rate that each site moves in mm per year. Their fault modeling is represented by the dark black line.
Global Positioning System velocity (triangles) and one standard error (bars) from Gan et al. (2000) compared to prediction of viscoelastic coupling model (heavy solid line), representing summed velocity contributions from four parallel faults (light dashed lines). SAF—San Andreas fault; DVF—Death Valley–Furnace Creek fault zone; HMF—Hunter Mountain–Panamint Valley fault zone; OVF—Owens Valley fault zone. Inset shows model rheology for Eastern California shear zone. SNB—Sierra Nevada block;B&R— Basin and Range Province; h is fault depth (depth of elastic layer) for three faults (a, b, or c), m is rigidity, h is viscosity. Arrows mark location of major shear-zone faults.
- Peltzer et al. (2001) use synthetic aperture radar interferometry (see my second update report for more on InSAR anslysis) to measure tectonic deformation that accumulated between 1992-2000.
- Alos, check out a more recent analysis using InSAR in CA here.
- The Coso Geothermal Field is the rainbow area in the northernmost part of the map. Indian Wells Valley is the green area to the south of the Coso Field. This is an area of elevated strain. The Garlock fault is the ~east-west black line in the center of the white inset box.
Surface velocity map obtained by averaging 25 interferograms of Los Angeles–Mojave region. One color cycle depicts 10 mm/yr of surface displacement along radar line of sight (at lat N348; ERS [Earth Resource Satellite] descending track trends S13.68W, radar looking westward at 238 off vertical incidence angle in middle of imaged swath). Gray areas are zones of low phase coherence that have been masked in processing. Black lines are active faults (Jennings, 1975). White box indicates subset of synthetic aperture radar (SAR) data that was used for profile in Figure 4. Note conspicuous shear strain along San Andreas fault and shear zone parallel to Blackwater–Little Lake fault system. Large deformation signal in northwest corner of frame is ground subsidence related to Coso volcanic and geothermal field (Fig. 1). Surface displacement associated with 1994 and 1995 Ridgecrest earthquakes is visible south of Coso area. Other patterns of surface deformation include ground subsidence due to groundwater withdrawal in Los Angeles and Lancaster areas (Fig. 1) and to seasonal change of water table level around dry lakes.
- Peltzer et al. (2001) plot observations from their radar data showing relative plate motion associated with dislocation along the Blackwater-Little Lake fault system.
Profiles of observed and modeled line-of-sight displacement projected on vertical plane perpendicular to shear zone. Gray dots are individual data points for all radar-image pixels included in box shown in Figure 3. Solid line shows 2 km running mean of observed displacement along profile length. Note that apparent standard deviation of projected data relative to average profile reflects in part displacement gradient parallel to fault strike and not only error in data. Groups of dots that deviate from dense part of profile are due to ground subsidence near lake shores and to surface displacement associated with Ridgecrest earthquakes (Figs. 1, 3). Short-dash line is profile predicted by long-term velocity model used to estimate interferometric baseline (Shen et al., 1996). Long-dash line is profile predicted by velocity model, including additional buried dislocation along Blackwater–Little Lake fault system. Parameters of added fault are given in text. Black dots and error bars (2s) are line-of-sight projections of horizontal velocities observed by GPS at stations of Yucca transect (Gan et al., 2000).
Background Literature – Little Lake fault
- Amos et al. (2013) presented an analysis of “tectonic, geomorphic, and volcanic” features to derive a slip rate for the Little Lake fault near Little Lake, California. This is just northwest of the 2019 Ridgecrest Earthquake Sequence. Here is their tectonic map.
Overview of active faults and regional topography of the Eastern California shear zone (ECSZ) and southern Walker Lane belt. Labeled faults are abbreviated as follows: ALF—Airport Lake fault, BF—Blackwater fault, GF—Garlock fault, KCF—Kern Canyon fault, LLF—Little Lake fault, OVF—Owens Valley fault, SNFF—Sierra Nevada frontal fault. OL—Owens Lake, IWV—Indian Wells Valley. Major historical earthquake surface ruptures in the Eastern California shear zone and Walker Lane belt are outlined in white, with stars denoting epicentral locations: OV—1872 Owens Valley, L—Landers 1992, HM—1999 Hector Mine. Active fault traces are taken from the U.S. Geological Survey Quaternary fault and fold database, with the exception of the Kern Canyon fault, taken from Brossy et al. (2012).
- Here is a geologic map from Amos et al. (2013) that shows the mapped faults and topographic controls of river drainage for the area.
Simplified geologic map of the Little Lake fault, highlighting Quaternary volcanic and alluvial deposits bearing on the Pleistocene drainage of Owens River through the Little Lake area. Map units are named and modified from Duffield and Bacon (1981). The 30 m elevation contours are taken from the National Elevation Database (NED). The 40Ar/39Ar dates are labeled as in Table 1. SNFF—Sierra Nevada frontal fault.
- Here is a figure that shows the topography at the Amos et al. (2003) slip rate site along the Owens River. They measured topographic profiles of the ground surface across topographic landforms. These profiles were taken along the thin white lines on the map on the left.
- On the right are the profiles from the western (B) and the eastern (C) profiles are shown on the right. They use these offset features, and the distance that they are offset, to calculate the slip rate here.
(A) 50 cm digital elevation model derived from terrestrial laser scanning (TLS) of displaced terrace risers in Little Lake narrows. (B–C) Stacked topographic profiles along the western and eastern edges of the Qt1 surface, respectively, used to reconstruct the total dextral offset of the Qt1-Qt2 terrace riser. Individual profiles were extracted perpendicular to the average riser orientation and were then projected onto a plane parallel to the local fault strike. Profile locations for each margin are shown in A. VE—vertical exaggeration.
- This is one of the coolest figures I found during my literature review. Amos et al. (2013) back calculate what the ground surface would look like if back in time, before the fault started to offset the topography here.
Geometric reconstruction of (A) the modern geomorphic configuration of the upper Little Lake narrows indicates between ~140 and 250 m of dextral offset for the base (B) and upper edge (C) of the eastern canyon wall. Geologic units are labeled as in Figure 3. The base image includes a hillshade image from our terrestrial laser scanning (TLS) survey, as
well as 10 m contours overlain on a National Elevation Database (NED) hillshade map. The map location is shown by the boxed area in Figure 3. Geologic units are labeled as in Figures 2 and 3.
- This is a cool figure, but not as cool as the above map. Amos et al. (2013) plot their slip rate estimates compared to published rates. First they show their observations of displacement relative to the age of the offset topographic landform. Then they plot slip rate estimates in the same manner.
(A) Compiled dextral displacements and (B) corresponding fault-slip rates as a function of age for the Little Lake, Blackwater, and Garlock faults. Linear regressions in A indicate constant slip rates through time. Geologic slip rate estimates in B are for time intervals since the respective age measurements. Geodetic measurements represent
interseismic deformation measured from interferometric synthetic aperture radar (InSAR) and global positioning system (GPS). […]
Background Literature – Garlock fault
- Astiz and Allen (1983) studied the seismicity of southern California and looked specifically at earthquake mechanisms associated with the Garlock fault. First we see their seismicity map for the region, then we zoom into the Garlock fault.
Southern California seismiclty during 1981 from Caltech-USGS catalog. The outer border corresponds to the limits of the southern California array. The inner frame is the limit of Figures 2 and 6. Notice the cluster of earthquakes along the Garlock fault trace and the smaller activity w~th respect to many other faults in southern California.
- Astiz and Allen (1983) plot the earthquake locations that they relocated for their analyses. This map shows a detailed map of the faults in the area..
Earthquake relocations from 1932 to 1981 in the Garlock fault zone. The light line corresponds to the 25-km-wide zone around the fault from which the earthquakes were taken from the catalog. The numbers m the figure corresponds to kilometers along the fault northeast from Gorman quarry (vertical axes in Figure 3). Sohd circles are quarries, and solid triangles are alignment array locations (from Keller et al., 1978). Faults are taken from Jennings and Strand (1969), Smith (1964), and Jennings et al. (1962).
- This figure shows the earthquake mechanisms for some events that Astiz and Allen (1983) worked on to show how many faults have strike slip mechanisms, but that there are changes in earthquake type (some thrust (compression) and normal (extension) events).
Focal mechanisms for selected events that occurred m the Garlock fault zone between 1977 and 1981 Numbers correspond to those m Table 3 Event 5 is a composite mechanism of six nearby events.
- McGill et al. (2009) late Pleistocene sediments (alluvial fan) and alluvial channels (with radiocarbon ages) to constrain an earthquake fault slip rate for the Garlock fault. First we see a tectonic map for the region.
Location of the Clark Wash site (large white circle) as well as other slip-rate and paleoseismic sites (small white circles) along the Garlock fault. AM—Avawatz Mountains; EPM—El Paso Mountains; GF—Garlock fault; PM—Providence Mountains; SAF—San Andreas fault; SLB—Soda Lake Basin; SM—Soda Mountains; SR—Slate Range; SSH—Salt Spring Hills; SV—Searles
Valley.
- These authors used a variety of observations to derive a statistical estimate (using probabilistic model) for a slip rate based on an estimate of offset and radiocarbon age (which both had a range of probabilities, plotted as a probability density function). This is really cool.
Probability density functions for left-lateral offset (A) and age (B) of Clark Wash that were assigned on the basis of quantitative constraints and subjective judgment (see text), and the resulting probability density function for the slip rate of the Garlock fault (C).
- Here is a compilation of their slip rate estimates (McGill et al., 2009).
Comparison of slip-rate estimates for the Garlock fault. The three values in italics, associated with boxes that outline sections of the fault, are the slip rates and formal uncertainties from Meade and Hager’s (2005) best-fitting elastic block model of available geodetic data. They report, however, that experience with a range of models suggests that true uncertainties are ~3 mm/yr. White-filled circles mark the locations of Holocene and Late Quaternary geologic slip-rate estimates. The Holocene rates that are constrained by radiocarbon dates and are thus considered most reliable are shown in bold […].
* more abbreviations and explanation in the paper
Background Literature – Owens Valley fault
- Kylander-Clark et al. (2005) use the lateral offset of plutonic dikes (igneous rocks) to constrain a long term slip rate across the Owens Valley fault. This map shows one of the dike pairs used in their analysis. By knowing the age of these dieks, and the distance that they have been offset, we can obtain a slip rate.
Locations of the Golden Bear and Coso dikes, adjacent to Owens Valley. Main figure shows the Golden Bear and Coso dikes striking into the valley, where they intrude 102 Ma plutons. Both the dikes and the plutons provide distinctive markers that can be matched across the valley and are consistent with 65 km of dextral displacement since 84 Ma. Inset shows other markers across Owens Valley that earlier workers suggested indicate from 0 to 65 km of dextral offset across the valley. Also shown are the traces of the Tinemaha fault (Stevens et al., 1997; Stevens and Stone, 2002) and intrabatholithic break 3 (IBB3; Kistler, 1993), which are hypothesized to accommodate offset of these markers. Note that the section of IBB3 between 38°N and 36.5°N is correlative with the eastern intrabatholithic break (EIB) of Saleeby and Busby (1993). Not all known locations of Independence dikes are indicated. Instead, patterned areas show only the densest parts of the dike swarm as defi ned by Glazner et al. (2003). AR—Argus Range; CR—Coso Range; IR—Inyo Range; WM—White Mountains
- Bacon and Pezzopane used trench excavations across earthquake faults to construct a prehistoric earthquake history for the Owens Valley fault. Below is their tectonic map for the region.
(A) Map of major Quaternary faults in the northern Eastern California shear zone and southern and central Walker Lane, as well as the locations of the Owens Valley fault. Faults are modified from Reheis and Dixon (1996) and Wesnousky (2005)
(B) Generalized fault and geology map of south-central Owens Valley, showing the A.D. 1872 Owens Valley fault rupture and major fault zones in the valley (modified from Hollett et al. [1991] and Beanland and Clark [1994]).
(For fault abbreviations, see their paper.)
- This map shows a more detailed view of the Owens Valley fault and the Owens Lake topography (Bacon and Pezzopane, 2007).
- This map shows the Bacon and Pezzopane (2007) field sites.
Shaded relief map of southern Owens Valley showing fault zones and the ages of the most recent prominent highstands and recessional shorelines of Owens Lake during the latest Quaternary (modified from Bacon et al., 2006).
Map of the field area and locations of paleoseismic study sites in relation to the A.D. 1872 Owens Valley earthquake fault trace near Lone Pine. Study sites are located on the Alabama Hills (AHS), Diaz Lake (DLS), and Manzanar (MZS) sections of the Owens Valley fault zone mapped by Bryant (1988) and Beanland and Clark (1994) from 1:12,000 aerial photographs.
- An essential part of any earthquake fault investigation is knowledge about the geologic units that are offset by the fault. Bacon and Pezzopane (2007) also described and interpreted the sediment stratigraphy in southern Owens Valley as part of their research.
Schematic composite stratigraphic column. The generalized stratigraphic and geochronologic relations, developed from exposures at the Alabama Gates and Quaker paleoseismic sites and Owens River bluffs near Lone Pine (Bacon et al., 2006), show the positions of radiocarbon dates, sequence boundaries, and event chronologies as discussed in the text.
- The geologic method (McCalpin, 1996) is based on the offset of geologic materials like sedimentary deposits or bedrock lithologic units. Below are trench logs showing the geologic units that Bacon and Pezzopane (2007) use to infer an earthquake history. Geologic evidence is “primary” evidence for earthquakes.
- Here is a time series showing the sedimentary and earthquake history as interpreted by Bacon and Pezzopane (2007).
Schematic depiction of stratigraphy and structural relations at the Quaker paleoseismic site prior to the penultimate event and after the A.D. 1872 earthquake (depictions A–H). The stratigraphy and structure exposed in trench T5 (Fig. 7) was retrodeformed and reconstructed one event at a time (while also accounting for other stratigraphic and
paleoseismic relations exposed in adjacent fault trenches and stratigraphic pits). The locations of sequence boundaries (SB0–SB4) are shown and can be referenced on Figure 5.
Background Literature – Earthquake History
- Here are the results of the paleoseismic (prehistoric earthquake history) investigation for the Owens Valley fault (Bacon and Pezzopane, 2007).
Fault segmentation and section map of central and southern Owens Valley showing overlap and possible distributive faulting and linkage between the northern segment of the Owens Valley fault (OVF) and southern White Mountains fault (WMF) near Big Pine. The trace of the A.D. Owens Valley fault rupture and section boundaries of Beanland and Clark (1994) and segment boundaries of dePolo et al. (1991) are shown in relation to the central and southern White Mountains fault and the location of the Black Mountain rupture of dePolo (1989). RRF—Red Ridge fault; LP—Lone Pine; I—Independence; BP—Big Pine; OSL—optically stimulated luminescence; PE—Penultimate event; APE—antepenultimate event; MRE—most recent event.
- McGill and Rockwell (1998) and Dawson et al. (2003) used fault trenching near El Paso Peaks, California to conduct a paleoseismic investigation along the Garlock fault. Below is a map that shows their trench site relative to tectonic features in the region.
Map showing the location of the trench site along the Garlock fault. Mountains are shaded, and valleys are shown open. Stippled areas are dry lake beds. SAF is San Andreas fault, DV is Death Valley, QM is Quail Mountains, LTC is Lone Tree Canyon, and SL is Searles (dry) Lake. Modified from McGill and Sieh [1993].
- McGill and Rockwell (1998) present this figure that shows an aerial image and a geologic map showing topographic features labeled in the aerial image. Note how there is a stream channel that is left-laterally offset.
Geomorphic and geologic expression ofthe Garlock fault at the trench site. (top) An annotated aerial photograph (courtesy U.S. Geological Survey) showing the trench site and selected geomorphic features. Unlabeled arrows mark the locations of fault scarps and benches. (bottom) A geologic map of the same area. Scale and orientation of the air photo are the same as shown on the map.
- Here is an annotated aerial image that was acquired when the light from the sun was at an angle that highlights the topographic features. This low-angle sun aerial photography method was pioneered by Bert Slemmons, one of the fathers of paleoseismology (who advised my HSU professor, Gary Carver when Gary was a student).
- Note how some features on the north side of the fault are to the left of features on the south side of the fault. This is why we call these left-lateral strike-slip faults. If one turns the image upside down, they will notice that the stuff on the other side of the fault still moves to the left. So, it does not matter what side of the fault one is standing on. I rotated the image below so we can see this first hand (see how features on the top of the image are offset to the left compared to the bottom of the image.
Annotated aerial photograph showing local tectonic geomorphology of the trench site. Scale is approximate. Solid lines are mappable fault traces, and dashed lines are inferred fault traces.
- This photo shows how huge and impressive the fault trenches were that Dawson et al. (2003) excavated for this study. Note the heavy equipment for scale. Read their paper to see the impressive amount of details that they used to unravel the earthquake history.
Annotated photograph illustrating some of the additional exposures that were created and documented. Note the location of trench 2, which had been backfilled at the time this photograph was taken. Trench 2 was later reexcavated to create the final and deepest exposure.
- This is but one example of the complicated sediment stratigraphy and faulting evidence that Dawson et al. (2003) used as a basis for their observations and interpretations. I show both the trench log (artwork) and the annotated panchromatic photo mosaic.
Event Y logs and three-dimensional excavation. Figure 7a is a log of a portion of trench 1 with evidence for event Y taken from McGill and Rockwell [1998]. Units shown shaded were interpreted to have been deposited in a collapse pit and then subsequently faulted by event Y. Figure 7b shows the three-dimensional excavation of this feature that shows units 90 and 92 actually being tubular in shape and units 78–42 correlative with units outside of the interpreted collapse feature. Scale varies in this mosaic due to three-dimensionality of the exposure, but the total width of the area shown is about 2.5 m. Dashed lines represent corners of 3-D exposure.
- These are complicated figures, yet elegant (McGill and Rockwell, 1998; Dawson et al., 2003). My favorite type of figure. The horizontal axis is time in calendar years (now is on the right and the past is on the left). The vertical axis is the thickness of the sedimentary deposits, with the ground surface at the top.
- Each earthquake is named an event (e.g. Event W). The dots represent radiocarbon ages (and the horizontal lines are the uncertainty associated with these ages). In the Dawson figure, the gray region represents the envelope of possible ages for the sediments between the radiocarbon ages. They assume a linear sedimentation rate between ages. Often people call these radiocarbon dates, but they are ages (it is not possible to obtain a date from radiocarbon age determinations because a date is a single day and these analyses are not that precise).
Variation of calibrated radiocarbon dates with stratigraphic depth. Errors shown are 2-sigma. The thick, diagonal line connecting the best estimates of most of the radiocarbon ages illustrates the simplest sedimentation rate history. Thinner, diagonal lines on either side represent the 2-sigma error envelope on the sedimentation rate, assuming that the date of each sample closely approximates its time of deposition. The faulting events visible within the trench are labelled along the right side of the graph, according to their stratigraphic depth; implied, preferred ages are plotted explicitly. Uncertain events are shown in parentheses. Stratigraphic depths to the earthquake horizons and to each depositional unit containing a radiocarbon sample were taken from the composite stratigraphic section shown in Figure 4.
Variation of calibrated radiocarbon dates with stratigraphic depth. Errors on the calibrated radiocarbon dates are 2-sigma. The curve connecting the solid circles connects the best estimates of the radiocarbon ages, providing the sedimentation rate. The dashed lines give the 2-sigma error envelope on the sedimentation rate.
- Here is a table showing McGill and Rockwell (1998) earthquake event times and return interval for each prehistoric earthquake.
- Here is the summary of prehistoric earthquake event times for this part of the Garlock fault (Dawson et al., 2003).
- 1906.04.18 M 7.9 San Francisco
- 2017.12.14 M 4.3 Laytonville
- 2016.11.06 M 4.1 Laytonville, CA
- 2016.11.03 M 3.8 Laytonville, CA
- 2016.08.10 M 5.1 Lake Pillsbury, CA
- 2015.08.30 M 3.6 Mendocino County, CA
- 2015.07.27 M 3.5 Point Arena, CA
- 2018.07.30 M 3.7 San Pablo Bay
- 2018.01.04 M 4.4 Berkeley
- 2019.07.04 M 6.4 Ridgecrest
- 2019.07.05 M 6.4 / 7.1 Ridgecrest Update #1
- 2019.07.18 M 6.4 / 7.1 Ridgecrest Update #2
- 2019.07.20 M 6.4 / 7.1 Ridgecrest Update #3
- 2016.02.23 M 4.9 Bakersfield
- 2015.12.30 M 4.4 San Bernardino, CA
- 2015.05.03 M 3.8 Los Angeles, CA
- 2015.04.13 M 3.3 Los Angeles, CA
- 2014.04.01 M 5.1 La Habra p-3
- 2014.03.29 M 5.1 La Habra p-2
- 2014.03.28 M 5.1 La Habra p-1
- 2016.08.04 M 4.5 Honey Lake, CA
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
- 2019.06.05 M 4.3 San Clemente Island
- 2018.04.05 M 5.3 Channel Islands
- 2018.04.05 M 5.3 Channel Islands Update #1
- 1994.11.17 M 6.7 Northridge, CA
- 1971.02.09 M 6.7 Sylmar, CA
Southern CA
Earthquake Reports
Social Media (UPDATE 2019.07.21
It was an unexpected surprise today when we ran into Roger Bilham in the field. He joined us for a few hours mapping a cross fault south of the M7.1 rupture. This fault that may be an important part of the puzzle of why the rupture stopped where it did. pic.twitter.com/bzQWoO4Mdn
— Tim Dawson (@timblor) July 19, 2019
Surface rupture and relative co-seismic right-lateral movement on the main fault trace of the Mw 7.1 #RidgecrestEarthquake. Images Google Earth & DigitalGlobe (2018-2019). pic.twitter.com/NvWp4rbDQN
— Sotiris Valkaniotis (@SotisValkan) July 19, 2019
And some more clear data of horizontal displacement (using CosiCorr) #Ridgecrestearthquakes fault ruptures. Dark gradient lines mark in detail the surface rupture trace – notice width of fault zone at southeast (Imagery from GoogleEarth/DigitalGlobe@2019) pic.twitter.com/0xMGDZTfP4
— Sotiris Valkaniotis (@SotisValkan) July 19, 2019
Southern part of Ridgecrest #earthquakes surface rupture now on Google Earth (you should use image timeline tool)
Amazing righ-lateral offsets of small gullies here. pic.twitter.com/aKVrMR1YQM— Robin Lacassin (@RLacassin) July 19, 2019
And the horizontal displacement results / image correlation (#MicMac) for #Ridgecrestearthquakes surface rupture, comparing pre- and post-eq high-res imagery. Profiles show coseismic offset (Not super-accurate – Imagery from GoogleEarth/DigitalGlobe@2019) pic.twitter.com/l7VlLZdhEM
— Sotiris Valkaniotis (@SotisValkan) July 19, 2019
Identified a few places where the #RidgecrestEarthquake ruptured some sort of underground pipelines that lead to leak of fuel or water. Possible #leak points are exactly on the main surface rupture (1-4m displacement). Images from Google Earth pic.twitter.com/aeZM9xees8
— Sotiris Valkaniotis (@SotisValkan) July 19, 2019
Another view of Ridgecrest #earthquakes right-lateral surface rupture from Google Earth (with image timeline tool) pic.twitter.com/4qgYuFcw8p
— Robin Lacassin (@RLacassin) July 19, 2019
A few more detailed views of the #RidgecrestEarthquake surface ruptures. Displacement from image correlation (with CosiCorr, using GoogleEarth & DigitalGlobe imagery) at two sites; complex faulting, main fault trace (NW-SE) is not linear or single, NE-SW ruptures also visible. pic.twitter.com/hszT17ZYEY
— Sotiris Valkaniotis (@SotisValkan) July 19, 2019
California sees a constant, irregular rhythm of earthquakes, many too small to feel. The larger quakes near Los Angeles earlier this month were two 2 heavy beats in an ongoing pattern, ones that set off thousands of others in the area. https://t.co/k51QNx94nk pic.twitter.com/Coq5ljDTYL
— The New York Times (@nytimes) July 19, 2019
That was then, this is now! This is totally not your grandfather's earthquake response. Women have been out there doing great stuff, from instrumentation to geology to communications. Just a few of the geotweeps involved: @GeoGinger @DonyelleDavis @earthquakemom @FaultyAndSalty pic.twitter.com/GShIn1EbY9
— Susan Hough (@SeismoSue) July 19, 2019
The Geotechnical Extreme Events Reconnaissance (GEER) Association report for the Ridgecrest Earthquake Sequence is now online. #RidgecrestEarthquake @USGSBigQuakes @CalConservation #CAgeologicalSurvey and @UCLAengineering collaboration w/@USNavy https://t.co/OQwenwYM2x pic.twitter.com/zBlkAaksMR
— Jason "Jay" R. Patton (@patton_cascadia) July 20, 2019
High resolution displacement from image correlation using pre- and post- eq Google Earth images The July 4 #RidgecrestEarthquake Mw 6.4 rupture is visible in detail, up to the junction with the Mw7.1 NW-SE rupture. A lot of noise/errors but even w/ GE can identify fault features. pic.twitter.com/VYxy53TiZ6
— Sotiris Valkaniotis (@SotisValkan) July 20, 2019
A new possible scenario that involves more than 3 fault plane sources with @esa #sentine1 @unavco GPS @IRIS_EPO data.
Thanks @patton_cascadia for your report 2 and @SotisValkan for your S-2 maps! #RidgecrestEarthquake #@FraxInSAR @maferp_13 @SimoneAtzori73 @USGS pic.twitter.com/DUe8dDp5vk— Vincenzo De Novellis (@VDN75) July 20, 2019
Spent a few more days in the Ridgecrest area this week mapping and measuring fault rupture south of Hwy 178. Found where the main strand offset Pinnacles Road. Parked the @Jeep right on the fault because I like to live dangerously! pic.twitter.com/pUIfAMmvTz
— Brian Olson (@mrbrianolson) July 20, 2019
Awesome GIF showing a before & after image of the surface faulting from the #RidgecrestEarthqauke. The dark staining is water from a pipeline that was broken by the ground shifting 2-3 feet sideways on the other side of the fault. Thank you @SotisValkan for the imagery. pic.twitter.com/HZTG3Aks0Q
— Brian Olson (@mrbrianolson) July 20, 2019
Sub cm-scale cracks observed today along the Garlock Fault in a few locations…also multiple relatively low altitude drones flight for high-res 3D mapping, oh, and a desert tortoise too. #RidgecrestEarthquake #drones #SfM pic.twitter.com/DwiN09i3F8
— Robert Leeper (@whatsbelow) July 21, 2019
A 3D view of the central NW-SE rupture w/offsets from image correlation. View towards E-SE pic.twitter.com/uHmHSeaAgx
— Sotiris Valkaniotis (@SotisValkan) July 21, 2019
This is not about Ridgecrest, but about the time, 20 June.
Apollo 11-16 installed seismometers recording moonquakes from '69 to '77. Four kinds were identified: (1) deep moonquakes (700km deep); (2) impact of meteorites; (3) thermal quakes caused by the expansion because of sun; and (4) shallow moonquakes (20km deep). #Apollo50th pic.twitter.com/oWoNfBFP0a
— iunio iervolino (@iuniervo) July 20, 2019
UPDATE 2020.12.09
Taking a deeper look into using USDA NAIP imagery for optical correlation – Ridgecrest 2019 earthquake. Advantages of NAIP; open public data, high resolution (0.6m), pre-processed/orthorectified & ready to use. N-S component shows only minimal artifacts from mosaicking. 1/4 pic.twitter.com/E0C9rTEZvu
— Sotiris Valkaniotis (@SotisValkan) December 9, 2020
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- Dawson, T. E., S. F. McGill, and T. K. Rockwell, Irregular recurrence of paleoearthquakes along the central Garlock fault near El Paso Peaks, California, J. Geophys. Res., 108(B7), 2356, https://doi.org/10.1029/2001JB001744, 2003.
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- Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
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- Guest, B., Pavlis, T.L., Goldberg, H., and Serpa, L., 2003. Chasing the Garlock: A study of tectonic response to vertical axis rotation in Geology, v. 31, no. 6, p. 553-556
- Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
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References:
Return to the Earthquake Reports page.
Well Well Well 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. 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.). 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.
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.
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.
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. 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.net. 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 earthjay.com are purely volunteer and do not reflect endorsement nor review from or by CGS.)
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.
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.
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).
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].
Here's some context for the M7.1 #earthquake today in California and its foreshock/aftershock sequence. It is well off the San Andreas Fault and north of the Garlock fault in the Eastern California Shear Zone. Read more from @Temblor about this area here: https://t.co/thInzw8ghF pic.twitter.com/NpLvDpyn1y — Dr. Kasey Aderhold (@kaseyaderhold) July 6, 2019 SLIPNEAR model along the aftershocks of the M6.4 mainshock. Slip inversion carried out with 2 different fault planes, one SE dipping (strike 45) from FMNEAR, and the other NW dipping from GCMT (strike 228). Slip distribution is quite similar in both cases (main slip zone stable) pic.twitter.com/gegZ9BSqR9 — Bertrand Delouis (@BertrandDelouis) July 7, 2019 Cumulative stress change caused by 4 July 2019 M=6.4 and the 7 July 2019 M=7.1 earthquakes on nearby strike slip faults, the red color represents increase seismic hazard Dr Kariche@IPGS2019 #RidgecrestEarthquake @DrLucyJones pic.twitter.com/jpGfqKhdzD — Jugurtha Kariche (@JkaricheKariche) July 7, 2019 Pixel tracking of @Planetlabs satellite images reveals the northern termination of the Mw 7.1 July 5th #earthquake. Result shows only ~16 km of rupture, with a minor transtensional splay in lower right. Slip profile, exhibits classic ‘dogtail’ taper. pic.twitter.com/S5CfsKd5AP — Chris Milliner (@Geo_GIF) July 7, 2019 A complete image of the Mw 7.1 Ridgecrest #earthquake showing amount of surface displacement measured by @planetlabs satellite imagery. Rupture is ~40 km in length with up to ~5m of fault slip. Fault trace has remarkably similar rupture geometry to 1999 Mw 7.1 Hector Mine event. pic.twitter.com/ORBA5D0gKz — Chris Milliner (@Geo_GIF) July 8, 2019 Came across this sandy vegetation mound out on the China Lake bed, which was cut in half by the fault rupture. Measured offset is approximately 8 feet. #earthquake #Ridgecrest pic.twitter.com/ok95QmfZQ8 — Brian Olson (@mrbrianolson) July 8, 2019 Estimated preliminary extent of the main rupture of Mw7.1 #earthquake #Ridgecrest CA, combining surface rupture traces from @CATnewsDE and @Geo_GIF (traced on @planetlabs imagery). Main rupture (red) extends at >45km. Black dots: reviewed epicenters USGS. Quaternary Faults: USGS. pic.twitter.com/Yq68sg86ub — Sotiris Valkaniotis (@SotisValkan) July 8, 2019 Great day mapping. Even made a 2 second cameo on PBS News hour. ;) — Nick Graehl (@nickgraehl) July 9, 2019 As promised, here are pictures of formerly high-speed dirt and environs! Enjoy these annotated photos from our recon mapping with J. Dolan and S. Attia yesterday of the Searles Valley EQ seq. near Ridgecrest, CA. Please contact me for more photos and information-ahatem@usc.edu pic.twitter.com/jZSIEaJuZY — Alex Hatem (@pride_of_lowell) July 9, 2019 A few more! pic.twitter.com/OckTe5LSx7 — Alex Hatem (@pride_of_lowell) July 9, 2019 OK, this really is the last one. The M6.4 earthquake strikes almost perpendicular to the track direction, and shows a deformation pattern that is more symmetric. We are mostly seeing the E-W movement of the fault in this case. [Thanks to @JAXA_en for a great radar satellite!] pic.twitter.com/joFeJ5tURk — Gareth Funning (@gfun) July 9, 2019 #RidgecrestQuake from Space This colorful map shows surface changes from the two earthquakes that rattled California last week. More here: https://t.co/qnj4B8zJm8 pic.twitter.com/w44MXwd3xL — NASA JPL (@NASAJPL) July 9, 2019 Some photos from today…#RidgecrestEarthquake pic.twitter.com/x5HrsdpJc6 — Nick Graehl (@nickgraehl) July 9, 2019 Surface rupture & displacement from the Mw 7.1 #Ridgecrest #earthquake CA as seen from #Sentinel2 images from @CopernicusEU. Animation using June 28 and July 8 images. Optical correlation map to follow later. pic.twitter.com/4cW0ovSIcM — Sotiris Valkaniotis (@SotisValkan) July 9, 2019 Quake ripped right through the flattest parts of the basin with maybe a little compression ridge in the southern stepover pic.twitter.com/NnSmKa3kSv — Bill Barnhart (@HawkeyeSeismo) July 9, 2019 It was a boots on the ground kind of day for CGS and USGS. Today we focused on measuring fault rupture offsets on the China Lake NAWS base #faultmapping #earthquake #Ridgecrest @CalConservation pic.twitter.com/L2PTZZF3ed — Ellie Spangler (@EllieSpangler) July 9, 2019 Data available; high-resolution figures and raster files for subpixel co-seismic offsets for the Mw6.4 and Mw7.1 #Ridgecrest, California #earthquakes, using #Sentinel2 images. #MicMac and CosiCorr files. Files uploaded in Zenodo repository: https://t.co/l10csPV4n7 pic.twitter.com/1MQIeeEzFj — Sotiris Valkaniotis (@SotisValkan) July 9, 2019 More from our #RidgecrestEarthquake coverage: DOC Drone footage south of Ransberg Road captures surface rupture. Photo: Roadway surface displacement – right-lateral offset approx. 6.5 ft and 3' vertical. Offset bottom of pic 5' ~ Footage: Nathaniel Roth. Photo: @mrbrianolson pic.twitter.com/6kDX8Tcc1e — DeptofConservation (@CalConservation) July 10, 2019 Surface fault ruptures from the July 4th Mw6.4 #Ridgecrest #earthquake visible using #Sentinel2 optical (normalized difference – Band4) and #Sentinel1 interferogram (made with SNAP at @esa_gep). Multiple traces, marked with orange arrows pic.twitter.com/70ePXUsiQD — Sotiris Valkaniotis (@SotisValkan) July 10, 2019 The Ridgecrest earthquakes: Torn ground, nested foreshocks, Garlock shocks, and Temblor’s forecast | https://t.co/1twVj9F84q https://t.co/x6aHPj0Az0 via #NSFfunded @temblor #California #Earthquake — temblor (@temblor) July 10, 2019 Azimuth phase gradient map, Range phase gradient map, Zoom in of range phase gradient map. It is filled with cracks!!!! #RidgecrestEarthquake pic.twitter.com/pJ5ydG5xR0 — Xiaohua Xu (@XiaohuaXu1) July 10, 2019 #Ridgecrest #Trona #earthquakes — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 10, 2019 Track 64 interferogram from Sentinel-1 data acquired by @esa. Remind me of the Hector Mine interferogram. #RidgecrestEarthquake #ridgecrestearthquakes pic.twitter.com/oqDQa5qC6e — Xiaohua Xu (@XiaohuaXu1) July 10, 2019 Following #Ridgecrest earthquake, @NASAJPL ARIA ALOS-2 interferogram, appears to show very small triggered slip on the Garlock fault. Bottom shows USGS Quaternary fault trace. pic.twitter.com/kppDaIkpsD — Chris Milliner (@Geo_GIF) July 9, 2019 I saw some spectacular faulting while putting in extra seismometers around Ridgecrest. pic.twitter.com/aOXz9aaNnY — Elizabeth Cochran (@escochran) July 10, 2019 Ken Hudnut (USGS), along w/partners Bob Fenton (FEMA Region IX Admin.) and Mark Ghilarducci (Director of CalOES) briefed @VP about the M7.1 earthquake that struck CA on July 5, 2019. Emphasis was placed upon coordination between CGS, USGS and @USNavy. https://t.co/suTpYkbe5z pic.twitter.com/lrSXC04T8W — USGS (@USGS) July 11, 2019 A preliminary semi-realistic finite element model of M6.9 Ridgecrest EQ, with fault curvature following pixel-tracked trace, CVM-H tomography, topography. Vertical fault is set for this stage. Green's function library on its way. @SotisValkan @chandraphyctc @shirzaei @ratlab3 pic.twitter.com/WSd9520fiT — Jay Tung (@jaytung_earth) July 11, 2019 Thanks to incoming InSAR images covering the complete rupture (below ALOS-2 interferogram from the @NASAJPL ARIA project), the information value provided by previous rapid slip inversions using strong motion data (SLIPNEAR) can be evaluated: pic.twitter.com/KDTC45kKuP — Bertrand Delouis (@BertrandDelouis) July 10, 2019 Map of permanent ground displacement due to M6.4 and M7.1 earthquakes near Ridgecrest California from NASA Caltech-JPL ARIA processing of JAXA ALOS-2 (unwrapped interferogram, path 65). This InSAR sensitive to west and up motion of ground. @zross_ relocated main and aftershocks pic.twitter.com/CuGtOv78nB — Eric Fielding (@EricFielding) July 10, 2019 Our Automatic Sentinel1 processing of co-seismic interferogram for the California Earthquakes with Mw. 7.1 and Mw 6.4 (Interferogram and LOS Displacement map) using #Sentinel1 @ESA_EO @CopernicusEU Track 64 (20190704-20190710) #IREA #CNR @FraxInSAR @claudiodeluca @VDN75 pic.twitter.com/ruGHFoQ0pv — Fernando Monterroso (@maferp_13) July 10, 2019 Left lateral faulting #SoCalEarthquake #drone #Ridgecrest #California pic.twitter.com/7QHGGXGm7G — Forrest Lanning (@rabidmarmot) July 11, 2019 #Sentinel2 mapped co-seismic #fault traces from the #Ridgecrest CA #earthquakes. While Sentinel-2 (Band 4 normalized difference) offers extravagant detail at certain parts, is missing traces in other areas. Interesting when in comparison with other sensors/methods & field. pic.twitter.com/VCb8ghN8WM — Sotiris Valkaniotis (@SotisValkan) July 11, 2019 My first look at #RidgecrestEarthquake rupture on Tues and first tweet ever!! pic.twitter.com/QFOpokctQR — Stephen Angster (@faultjumper) July 11, 2019 Found our BIGGEST offset yet for the fault that caused the M7.1 earthquake. This channel is offset about 13 feet! #ridgecrestearthquake #earthquake #ridgecrest pic.twitter.com/EQCh3Z9DBj — Brian Olson (@mrbrianolson) July 12, 2019 An amazing week working with colleagues from @CalConservation California Geological Survey and the @usgs mapping ruptures from the earthquakes in Ridgecrest. Thanks to the residents who have been welcoming and the @USNavy for incredible logistical support. #ridgecrestearthquakes pic.twitter.com/Yqs8yAZtLY — Tim Dawson (@timblor) July 12, 2019 This animation shows preliminary results from precise relocation of the Ridgecrest foreshock sequence, up to the the time of occurrence of the M 7.1 mainshock. Full details at: https://t.co/Gm3GuSPt0s pic.twitter.com/RfIijTiHfu — USGS (@USGS) July 12, 2019 A very preliminary fault slip model for #RidgecrestEarthquake, using data from GPS, @esa Sentinel-1, @ALOS2_JAXA, optical imagery from @planetlabs by @Geo_GIF. Model, surface displacement and Coulomb stress available at https://t.co/SSyQaHdJYh. pic.twitter.com/TZ8PQop7cZ — Xiaohua Xu (@XiaohuaXu1) July 12, 2019 CGS and USGS teams mapped fault offsets that were an order of magnitude less than yesterday’s, but in someways much cleaner to measure. Here is a shrub dune left-laterally offset 30 cm by the July 4 M 6.4 pic.twitter.com/F7UH6f82An — Tim Dawson (@timblor) July 13, 2019 Updated rupture map of #Ridgecrest earthquake. Faults mapped from @Planetlabs offsets, and Sentinel-1 wrapped and phase gradient. Juncture of Mw 6.4 and 7.1 is highly complex. Green = primary fault rupture — Chris Milliner (@Geo_GIF) July 12, 2019 Today's M4.9 aftershock was recorded by a temporary seismometer at ~2 km epicentral distance. It recorded a peak acceleration of 14%g. Intensities in Ridgecrest imply accelerations in the same range, or maybe even higher locally. This illustrates an important point. pic.twitter.com/ruefagOhdT — Susan Hough (@SeismoSue) July 13, 2019 Headed home after a week working on response to #RidgecrestEarthquake. Impressive effort by all involved from #USGS #CGS #UNR #EERI and many more. A few of my favorite photos: ~4 m offset dirt road, 108F temps, central part of M7.1 rupture with @timblor and @chrisduross for scale pic.twitter.com/B8fIfaNxti — Ryan Gold (@runr447) July 13, 2019 'NASA's ARIA Team Maps California Quake Damage' news article from the #NASA_App @NASAJPL https://t.co/Kyk34SmN6q — Eric Fielding (@EricFielding) July 13, 2019 Growing evidence for Garlock fault having very small triggered slip. Both ALOS-2 wrapped phase and Sentinel 1 aziumuthal gradient map show small slip for ~35 km alongfault. @XiaohuaXu1 pic.twitter.com/bKSbGmWO9U — Chris Milliner (@Geo_GIF) July 10, 2019 This @UNVACO map shows how GPS stations moved from just before to just after the #RidgecrestEarthquake. The arrows show the direction & size of motion. This represents how much the ground moved at each site. The scale arrow in the lower left represents 100 mm, or 10 cm (~4 in). pic.twitter.com/tQzvNGugms — IRIS Earthquake Sci (@IRIS_EPO) July 8, 2019 The possible fault sources of the #ridgecrestearthquake by analytical solution combining #sentinel1 #sentinel2 @UNAVCO gps and @USGS faultlines data. — Vincenzo De Novellis (@VDN75) July 13, 2019 Ground deformation after #Ridgecrest earthquake using #Sentinel1 ascending dataset. #RidgecrestEarthquake #RIKEN #RIKEN_AIP #Earthquake #Deformation pic.twitter.com/EFQadAoaZ7 — Sadra Karimzadeh (@Sadra_Krmz) July 13, 2019 Why historical seismology? Some years ago @Kate6HTN and I wrote a paper on the 1872 Owens Valley earthquake, presenting evidence that the rupture continued south of Lone Pine, to Haiwee. pic.twitter.com/VNND3HfniX — Susan Hough (@SeismoSue) July 14, 2019 "Scientists from the USGS and other organizations continue field work and analyses". Here is a release of the surface rupture map:https://t.co/cC53bdzEQZ pic.twitter.com/tS3p5t9c6z — Stéphane Baize (@stef92320) July 13, 2019 More results using @ALOS2_JAXA data available on https://t.co/SSyQaHdJYh . What really needed is the other look direction. Waiting for 16th Sentinel-1. Also check out the north west corner. That's central valley going down. pic.twitter.com/419xh9uJQi — Xiaohua Xu (@XiaohuaXu1) July 14, 2019 Here it is. With @YorgosBz and @ESM_db we've been looking at the (possibly) impulsive features of ground motions from the #californiaearthquake, as identified by Baker's 2007 algorithm. Polygon is source projection, E is epicenter. (Note: just preliminary, no conclusions yet.) pic.twitter.com/4vucfl8nuV — iunio iervolino (@iuniervo) July 14, 2019 Last 12 days on a seismogram ~15km S of #Ridgecrest showing:#Ridgecrest #Trona #earthquake — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 15, 2019 Many are asking *why* Ridgecrest didn't suffer more damage from the M7.1 earthquake. I noticed the peak ground accelerations measured IN Ridgecrest were actually LESS for the M7.1 despite it releasing 11x more energy. pic.twitter.com/UyUGVYyNh0 — Brian Olson (@mrbrianolson) July 15, 2019 Wanted to say I was honored to join the team collecting location & offset data from recent Ridgecrest earthquakes. From huddling under tables w/ @kwhudnut & @earthquakemom during the M7.1 to sweating profusely on the dry lake bed, I valued all of it. #TeamCGS #TeamUSGS pic.twitter.com/Yxzf8yrQ15 — Brian Olson (@mrbrianolson) July 14, 2019 Another preliminary fault slip model for #RidgecrestEarthquake, using data from @esa #Sentinel1 and @UNAVCO GPS. @USGS faultlines (black) & @IRIS_EPO earthquakes distribution (red) are also shown; the darkest blue corresponds to ~5.5 m slip value.@SimoneAtzori73 @EricFielding pic.twitter.com/gSTzlTDD4X — Vincenzo De Novellis (@VDN75) July 15, 2019 Well, at AGU it is going to be called: — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 16, 2019 Another phase gradient image from the M7.1 Hector Mine Earthquake. Not as many conjugate fractures as the M7.1 in Ridgecrest. pic.twitter.com/pwTr8vEIlI — David Sandwell (@sandwell_david) July 14, 2019 And it's official, or very close to it: the earthquake sequence formerly known as Searles Valley will henceforth be known, in official circles as well as the media, as the 2019 Ridgecrest sequence. pic.twitter.com/cWICiSZ8Ry — Susan Hough (@SeismoSue) July 16, 2019 Earthquake now officially renamed! pic.twitter.com/vNwjzQob3z — Susan Hough (@SeismoSue) July 16, 2019 Post-seismic slip (~2-6cm) along the fault rupture of both Mw6.4 & Mw 7.1 #Ridgecrest #earthquakes, as hinted by #Sentinel1 #InSAR for the time interval June 10 – June 16. pic.twitter.com/71oFb0Z4A4 — Sotiris Valkaniotis (@SotisValkan) July 16, 2019 Descending interferogram #InSAR from #Sentinel1 data, #Ridgecrest #earthquake sequence. Rupture trace from previous InSAR & optical data. July 4 – July 16. Processed with DIAPASON at @esa_gep pic.twitter.com/VThrEHNqj9 — Sotiris Valkaniotis (@SotisValkan) July 16, 2019 Unwrapped (LOS displacement) descending interferogram #InSAR from #Sentinel1 data, #Ridgecrest #earthquake sequence. Rupture trace from previous InSAR & optical data. July 4 – July 16. Processed with DIAPASON at @esa_gep pic.twitter.com/Qs8DOuUjix — Sotiris Valkaniotis (@SotisValkan) July 16, 2019 A new phase gradient map from @Sentinel1a descending track 71 for #ridgecrestquake. Data quality is just better. And a screen shot that shows sharp creep on the Garlock. Soon these will be available on https://t.co/sUnZG76gzM. pic.twitter.com/ovIzBTgS9p — Xiaohua Xu (@XiaohuaXu1) July 17, 2019 Garlock Fault @AmauryVallage pic.twitter.com/6MlmdcWouK — Sotiris Valkaniotis (@SotisValkan) July 16, 2019 Just released: 2019 Ridgecrest Earthquake Sequence: July 4, 2019–July 16, 2019. Download or view a text version at https://t.co/C864c132ol pic.twitter.com/jHRm0e0fLp — USGS (@USGS) July 17, 2019 And the ascending pair from #Sentinel1, #Ridgecrestearthquake. Gradient render from unwrapped LOS displacement map (higher quality 20m from SNAP). Processing in @esa_gep. pic.twitter.com/IzaHeceXUU — Sotiris Valkaniotis (@SotisValkan) July 17, 2019 Some more animations from #Sentinel2 imagery, sgowing possible liquefaction/lateral-spreading or surface distrurbance in #Searles Lake from the Mw 7.1 #RidgecrestEarthquake 2/2 pic.twitter.com/1MXynzpvQR — Sotiris Valkaniotis (@SotisValkan) July 17, 2019 Building on our previous InSAR result across the #californiaearthquake #Ridgecrest we've been able to determine the East-West and Vertical components of movement using two opposing @CopernicusEU Sentinel-1 lines-of-sight. Over 90 cm of westward movement is detected! pic.twitter.com/LcIMMk9HkI — NPA SatelliteMapping (@CGGNPA) July 17, 2019 Instrumental ground motion observations of the #ridgecrestearthquake sequence. Portable real-time stations get us good close in strong-motion measurements of the Mw 4.9 and other aftershocks. @usgs_seismic @usgs @GeoGinger pic.twitter.com/o1Eka8K1lD — Daniel McNamara (@DanielEMcNamara) July 17, 2019 Came across an elongate cobble that was FLIPPED over by the earthquake shaking. This is fairly flat ground, no slope for gravity assistance. Suggests some pretty strong shaking in this area south of Hwy 178. #RidgecrestEarthquake #ridgecrest #earthquake pic.twitter.com/l1rDnFogYQ — Brian Olson (@mrbrianolson) July 18, 2019 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. pic.twitter.com/wZi8H9i78O — Sotiris Valkaniotis (@SotisValkan) July 18, 2019 Shaken, not stirred! We observed this strong ground motion indicator of a toppled tufa pile along the SW strand of the Mw 7.1 Ridgecrest rupture. These tufa piles are least 14,000 years old and have been thru many regional EQs, but one decided to fall now! James Dolan for scale. pic.twitter.com/KcyE4OAnKs — Alex Hatem (@pride_of_lowell) July 18, 2019 These before & after #Landsat panchromatic band images show a surface rupture near the epicenter of the #Ridgecrest 7.1 #earthquake. — USGS Landsat Program (@USGSLandsat) July 18, 2019 Preliminary fault slip distribution for 7.1 #Ridgecrest earthquake measured from pixel tracking of Sentinel-2 optical images. Rupture shows compact slip asperity near epicenter, with max. being ~4 m, consistent with field observations. pic.twitter.com/yGQ1usV2DQ — Chris Milliner (@Geo_GIF) July 18, 2019 Preliminary rupture models for M6.4 and M7.1 by joint inversions of strong-motion, GPS, and teleseismic. Seems possible that it could have slipped twice. #RidgecrestEarthquake pic.twitter.com/jUYE8hUwsE — Chengli Liu (@chengli_liu) July 15, 2019 How Two Big Earthquakes Triggered 16,000 More in Southern California – The New York Times. Love the animations! @nytimes https://t.co/qL4A5cPUb7 — Susan Hough (@SeismoSue) July 19, 2019 The Geotechnical Extreme Events Reconnaissance (GEER) Association report for the Ridgecrest Earthquake Sequence is now online. #RidgecrestEarthquake @USGSBigQuakes @CalConservation #CAgeologicalSurvey and @UCLAengineering collaboration w/@USNavy https://t.co/OQwenwYM2x pic.twitter.com/zBlkAaksMR — Jason "Jay" R. Patton (@patton_cascadia) July 20, 2019
Well, yesterday I was preparing some updates to the Ridgecrest Earthquake following my field work with my colleagues at the California Geological Survey (where I work) and the U.S. Geological Survey. We spent the week documenting surface ruptures associated with the M 6.4 and M 7.1 Ridgecrest Earthquake Sequence. (it is currently named the Searles Valley Earthquake Sequence, but I am calling it the Ridgecrest Earthquake)
Impact of Earthquake Now I can get back to working on a Ridgecrest update… stay tuned. (the maps are already made) I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this: FOS = Resisting Force / Driving Force When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.
Nowicki Jessee and others (2018) is the preferred model for earthquake-triggered landslide hazard. Our primary landslide model is the empirical model of Nowicki Jessee and others (2018). The model was developed by relating 23 inventories of landslides triggered by past earthquakes with different combinations of predictor variables using logistic regression. The output resolution is ~250 m. The model inputs are described below. More details about the model can be found in the original publication. We modify the published model by excluding areas with slopes <5° and changing the coefficient for the lithology layer "unconsolidated sediments" from -3.22 to -1.36, the coefficient for "mixed sedimentary rocks" to better reflect that this unit is expected to be weak (more negative coefficient indicates stronger rock).To exclude areas of insignificantly small probabilities in the computation of aggregate statistics for this model, we use a probability threshold of 0.002.
Here is an excellent educational video from IRIS and a variety of organizations. The video helps us learn about how earthquake intensity gets smaller with distance from an earthquake. The concept of liquefaction is reviewed and we learn how different types of bedrock and underlying earth materials can affect the severity of ground shaking in a given location. The intensity map above is based on a model that relates intensity with distance to the earthquake, but does not incorporate changes in material properties as the video below mentions is an important factor that can increase intensity in places.
Zhu and others (2017) is the preferred model for liquefaction hazard. The model was developed by relating 27 inventories of liquefaction triggered by past earthquakes to globally-available geospatial proxies (summarized below) using logistic regression. We have implemented the global version of the model and have added additional modifications proposed by Baise and Rashidian (2017), including a peak ground acceleration (PGA) threshold of 0.1 g and linear interpolation of the input layers. We also exclude areas with slopes >5°. We linearly interpolate the original input layers of ~1 km resolution to 500 m resolution. The model inputs are described below. More details about the model can be found in the original publication.
Here is a map that shows a comparison of modeled shaking intensity for both the M 6.9 Molucca Strait (the left panel) and M 7.3 Halmahera (the right panel) earthquakes. The legend shows the MMI scale, which I discuss above.
Annual probability of experiencing a tsunami with a height at the coast of (a) 0.5m (a tsunami warning) and (b) 3m (a major tsunami warning).
Regional tectonic setting with plate boundaries (MORs/transforms = black, subduction zones = teethed red) from Bird (2003) and ophiolite belts representing sutures modified from Hutchison (1975) and Baldwin et al. (2012). West Sulawesi basalts are from Polvé et al. (1997), fracture zones are from Matthews et al. (2011) and basin outlines are from Hearn et al. (2003).
Along its western margin, the Philippine Sea plate is associated with a zone of oblique convergence with the Sunda plate. This highly active convergent plate boundary extends along both sides the Philippine Islands, from Luzon in the north to Sulawesi in the south. The tectonic setting of the Philippines is unusual in several respects: it is characterized by opposite-facing subduction systems on its east and west sides; the archipelago is cut by a major transform fault, the Philippine Fault; and the arc complex itself is marked by volcanism, faulting, and high seismic activity. Subduction of the Philippine Sea plate occurs at the eastern margin of the archipelago along the Philippine Trench and its northern extension, the East Luzon Trough. The East Luzon Trough is thought to be an unusual example of a subduction zone in the process of formation, as the Philippine Trench system gradually extends northward (Hamburger and others, 1983).
Topographic and tectonic map of the Indonesian archipelago and surrounding region. Labeled, shaded arrows show motion (NUVEL-1A model) of the first-named tectonic plate relative to the second. Solid arrows are velocity vectors derived from GPS surveys from 1991 through 2001, in ITRF2000. For clarity, only a few of the vectors for Sumatra are included. The detailed velocity field for Sumatra is shown in Figure 5. Velocity vector ellipses indicate 2-D 95% confidence levels based on the formal (white noise only) uncertainty estimates. NGT, ew Guinea Trench; NST, North Sulawesi Trench; SF, Sumatran Fault; TAF, Tarera-Aiduna Fault. Bathymetry [Smith and Sandwell, 1997] in this and all subsequent figures contoured at 2 km intervals
3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.
(A) Location and major tectonic features of the Molucca Sea region. Small, black-fi lled triangles are modern volcanoes. Bathymetric contours are at 200, 2000, 4000, and 6000 m. Large barbed lines are subduction zones, and small barbed lines are thrusts. (B) Cross section across the Halmahera and Sangihe Arcs on section line B. Thrusts on each side of the Molucca Sea are directed outward toward the adjacent arcs, although the subducting Molucca Sea plate dips east beneath Halmahera and west below the Sangihe Arc. (C) Inset is the restored cross section of the Miocene–Pliocene Weda Bay Basin of SW Halmahera on section line C, fl attened to the Pliocene unconformity, showing estimated thickness of the section
Map of the Molucca Sea, eastern Indonesia, showing I~tions of seismic refraction lines (solid straight lines) and gravity traverses (duhed-dotted lines). Thrust faults are shown with teeth on hanging wall. Triangles represent active volcanoes defining the Sangihe and Halmahera magmatic arcs. Isobath interval is 1 km from Mammericks et al. [1976].
Gravity model for the central Molucca Sea. (II) Crustal model with layers designated by their density contrasts and refraction control points by open circles and vertical bars. (b) Mantle structure used in modeling the gravity profiles in the central Molucca Sea. Figure 124 fits into the small box at the apex of the inverted-V-ehaped lithosphere. Slab dimensions are controlled by earthquake foci (dots) from Hlltherton 11M Dickinaon [1969J, and mantle densities are taken from Grow 11M Rowin [1975J. The column at the left shows assumed densities for the range of depths between the tick marks. The small v pattern represents oceanic crust, and island arc crust is designated by a short parallel line pattern. East is to the right of the figure.
Location map and active faults of the Molucca Sea region. Fault colours: blue, convergence; red, transvergence; yellow, divergence; grey, uncertain motion. Fault abbreviations: CF, Catabato Fault; GF, Gorontalo Fault; NST, North Sulawesi Trench; PKF, Palu-Koro Fault; SF, Sorong Fault.
Sketch geological map of Halmahera based on Apandi & Sudana (1980), Silitonga et al. (1981), Supriatna (1980) & Yasin (1980) and modified after our own observations. Note in particular the absence of thrusting in the NE arm and the major NE-SW fault (the Subaim Fault) running parallel to the south side of Kau Bay.
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Updated #aftershocks of the yesterday Mw 7.3 Halmahera #earthquake, seems the EQ has low aftershocks productivity. The Mc is quite large (~3.5) in this region due to the lack of local (distance <100 km) seismic station, but the regional coverage is good. #seismology #gempa pic.twitter.com/wEzwn9fJvR — Dimas Sianipar (@SianiparDimas) July 15, 2019 Mw=7.4, HALMAHERA, INDONESIA (Depth: 17 km), 2019/07/14 09:10:50 UTC – Full details here: https://t.co/dNG7xZttM4 pic.twitter.com/BrD8FJ8ofn — Earthquakes (@geoscope_ipgp) July 14, 2019 Explore the complex region where the M7.3 #Indonesia #earthquake occurred using the IRIS Interactive Earthquake Browser. The size of the dot indicates the magnitude & the color indicates the depth. You can even look at eq hypocenter locations in 3D! https://t.co/Gs3ykBEp0y pic.twitter.com/wEK4g6srok — IRIS Earthquake Sci (@IRIS_EPO) July 14, 2019 potential #tsunami after #Halmahera #earthquake. Tsunami impact highly depends on a still very uncertain rupture mechanism. Recorded wave amplitude of 10 cm near #Gebe. — CATnews | Andreas M. Schäfer (@CATnewsDE) July 14, 2019 potentially expected #aftershocks for today's #Halmahera #earthquake, #Indonesia @ShakingEarth pic.twitter.com/R9RUghePs2 — CATnews | Andreas M. Schäfer (@CATnewsDE) July 14, 2019 BMKG: Halmahera Selatan Masuk Wilayah Seismik Aktif dan Kompleks https://t.co/8XcNfJMQEy — Indonesiainside.id (@indoinsidenews) July 15, 2019
There have been well over 1000 aftershocks with magnitudes M ≥ 0.5. https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/executive From the USGS: Analog seismograph record from an instrument near the Grapevine. Mainshock and large aftershock are in view. Photo taken at CGS HQ in Sacramento. #RidgecrestEarthquake #SearlesValleyEarthquake pic.twitter.com/HmL5g0I8Yy — Nick Graehl (@nickgraehl) July 5, 2019 The fault also ruptured across Randsburg Wash Road (south of Hwy 178) and offset it approx 1.5 feet. The offset is more here because it’s focused on 2-3 fault strands instead of 5-6 strand at Hwy 178. #ridgecrest #earthquake pic.twitter.com/GSVbTd60Kw — Brian Olson (@mrbrianolson) July 5, 2019 I ran the coseismics through G-FAST and got the following slip model for the Searles Valley EQ. G-FAST adds some extra fault real-estate (i.e. to NE) to allow for bilateral rupture, but does a good job putting slip only where it should be. pic.twitter.com/EleHejDZez — Brendan Crowell (@bwcphd) July 5, 2019 Earthquake aftershocks could last months or even years, scientists say https://t.co/YMoq0pLMVX @r_valejandra — Ron Lin (@ronlin) July 5, 2019 Aftershocks are continuing and damage/injury reports are becoming more detailed after today's magnitude 6.4 between the Sierras and the Mojave Desert, near Ridgecrest, CA. See our recent web article for basic earthquake information and safety tips: https://t.co/y41yRoHZYP. pic.twitter.com/oCniHnRXry — SCEC (@SCEC) July 4, 2019 Ridgecrest earthquake video: Parents, kids scream as 6.4-magnitude quake rattles stage during July 4th performance https://t.co/OIcBHswdnf via @abc7 — CaliforniaDisasters (@CalDisasters) July 6, 2019 New surface rupture from latest earthquake. 35.64900, -117.48240 pic.twitter.com/xgBUOExshK — Rich Koehler (@faultcreeper) July 6, 2019 Preliminary finite fault model for today's California earthquake. ~50 km long, ~20 s duration, peak slip ~3m in this model. Deep slip at NW end of model probably not real. Updates will follow. pic.twitter.com/i5q4iFK0yF — Gavin Hayes (@gph_seismo) July 6, 2019 Another huge earthquake in Los Angeles! #earthquake #LosAngeles #california pic.twitter.com/c7hVHLrNaN — Max Graham (@maxgraham22) July 6, 2019 7.1 just happened! The seismograph at #GriffithObservatory was going crazy during the #SoCal #earthquake #StrangerThings #RidgecrestEarthquake #LasVegas #vegasearthquake #California pic.twitter.com/Hc0Gv5d5ey — CantTameMe (@CantTameMe69) July 6, 2019 Earthquake batters Trona: Rockslides cut off town; water is scarce https://t.co/ugYcpujKiE — L.A. Times: L.A. Now (@LANow) July 6, 2019 #Video taken at Morongo Casino in Cabazon, California, at the moment 6.9 mag earthquake strikes in southern California minutes ago. pic.twitter.com/BLQxO0ZqBq — 1st Breaking News® 🇲🇽 (@1stBreakingNews) July 6, 2019 7.1 magnitude earthquake 150 miles away in Ridgecrest, Ca. This is in my 6th (very top) floor apartment in Glendale, Ca. Turn your volume on for the full effect! #earthquakes #earthquake #EarthquakeLA #earthquakecalifornia @earthquakeBot @USGSBigQuakes pic.twitter.com/ZCokTSHvgM — russell john (@russelljohnnn) July 6, 2019 7.1 magnitude earthquake 150 miles away in Ridgecrest, Ca. This is in my 6th (very top) floor apartment in Glendale, Ca. Turn your volume on for the full effect! #earthquakes #earthquake #EarthquakeLA #earthquakecalifornia @earthquakeBot @USGSBigQuakes pic.twitter.com/ZCokTSHvgM — russell john (@russelljohnnn) July 6, 2019 Aftershock activity comparison: Largest expected aftershock M6.0-6.3 is still to come (or maybe not) pic.twitter.com/q2Bid6C6w0 — CATnews | Andreas M. Schäfer (@CATnewsDE) July 6, 2019 Too amped to sleep. https://t.co/B0y7x6xhwY — Tiegan Hobbs (@THobbsGeo) July 6, 2019 DOC's Acting State Geologist, Tim McCrink, on @kcranews showing the #RidgecrestQuake area seismic faults and explaining the aftershock sequence. https://t.co/44NWJUiDq2 @Cal_OES — DeptofConservation (@CalConservation) July 6, 2019 Hold the train! near Trona pinnacles with @faultcreeper close to 1 m RL offset. #earthquake #ridgecrestearthquake pic.twitter.com/J9Z8npqZH5 — Ian Pierce (@neotectonic) July 6, 2019 Second quake did not rupture 395 or any roads east of coso junction pic.twitter.com/HPz2DfRo0O — Ian Pierce (@neotectonic) July 6, 2019 Creating two pictures, one from the M6.4 to the M7.1 (top), and the second from the M7.1 onwards (bottom). This, to separate the two sequences (although that of the M6.4 continues to some extent after the M7.1). The green and blue lines materialize the M6.4 aftershock sequence. pic.twitter.com/atYSvNJvCp — Bertrand Delouis (@BertrandDelouis) July 6, 2019 Just ran the Ridgecrest slip model through G-FAST, M7.19, a bit over 3 m slip, still preliminary. pic.twitter.com/hmUD6uSRg4 — Brendan Crowell (@bwcphd) July 6, 2019 Back Projection for M 7.1 CENTRAL CALIFORNIA #EARTHQUAKE https://t.co/ajDkYpZFRS pic.twitter.com/B1Qg78bpbI — IRIS Earthquake Sci (@IRIS_EPO) July 6, 2019 Today's large EQ in USA is a good example of how its not large earthquakes that kill people but poorly built/designed buildings and infrastructure. So far no reported fatalities. BBC News – California earthquake: Larger 7.1 magnitude quake hitshttps://t.co/PfVSqJPFQS — tectonictweets (@tectonictweets) July 6, 2019 Animation of the #SoCalEarthquake sequence made using the IRIS Interactive Earthquake Browser. This covers the time period 7/4-to 7/6 17:00 UTC and uses USGS #earthquake locations. https://t.co/o0PzvGOiJH pic.twitter.com/f12FJXhi13 — IRIS Earthquake Sci (@IRIS_EPO) July 6, 2019 Permanent deformations predicted on the base of the finite fault provided by #USGS, through waveform inversion, for the M 7.1 #EarthquakeLA. — Simone Atzori (@SimoneAtzori73) July 6, 2019 View the #SoCalQuake sequence on the IRIS Interactive Earthquake Viewer. You can even view the #earthquake hypocenters in 3D (like in the black image below) and animate the aftershock sequence! https://t.co/Gs3ykBEp0y pic.twitter.com/RsK6kQ2T4v — IRIS Earthquake Sci (@IRIS_EPO) July 6, 2019 Earthquakes near Ridgecrest were clearly in an red zone in the Coulomb failure stress changes (ΔCFS) analysis by Verdecchia and Carena, Tectonics (2016) 10.1002/2015TC004091. Would be great to see an after-event update? and see the impact on Garlock Fault. pic.twitter.com/VWh6po02dg — Anne-Sophie Meriaux 🇪🇺 (@Tecto_Asm) July 6, 2019 Right offsets pic.twitter.com/cv5gM1ms9N — Rich Koehler (@faultcreeper) July 6, 2019 This mornings findings in the Trona pinacles area along the #Ridgecrest surface rupture with @neotectonic Think we Found southern extent of rupture pic.twitter.com/YhkgQA2aUF — Rich Koehler (@faultcreeper) July 6, 2019 DOC California Geological Survey's Janis Hernandez measures an offset on Highway 178. She's 1 of 20 geologists deployed to survey the effects of #RidgecrestEarthquake #earthquakeresponse @USGS @Cal_OES #cgs pic.twitter.com/LY3vv0H9uR — DeptofConservation (@CalConservation) July 6, 2019 Chris was in the field this morning and saw an offset anthill with about ~ 1 ft RL displacement from M7.1. His pictures below: pic.twitter.com/WwqXq1giz6 — Danielle Madugo (@DanielleVerdugo) July 6, 2019 1m of right lateral displacement of tire tracks, a dirt road and a fence. Pretty amazing. And we are at the southern part of the rupture pic.twitter.com/Fl4cIKvyr1 — Colin Chupik (@ChupikColin) July 6, 2019 More from today. Tiny pull aparts, pressure ridges and wide zones of deformation… pic.twitter.com/TjJwCVOBOJ — Colin Chupik (@ChupikColin) July 6, 2019 Just got into cell range from the 7.1 rupture where it crosses the 178. Just south of there, it crosses a dirt road with 1 strand with ~2ish ft RL and some vertical and another strand with very minimal RL and diffuse vertical displacement. NBC is camped on the RL and main strand. pic.twitter.com/54qxfaEHrk — Danielle Madugo (@DanielleVerdugo) July 6, 2019 Latest view of aftershocks from the SoCal quakes + slip model of today's M7.1 rupture (projected on the surface+aligned along the fault). Looks like today's rupture went SE past the intersection of the two faults. SW-NE fault has been less active today in terms of aftershocks. pic.twitter.com/td2V75ukNS — Stephen Hicks 🇪🇺 (@seismo_steve) July 6, 2019 @Planetlabs satellite images shows complex and distributed rupture of the July 4th Mw 6.4 Ridgecrest #earthquake. You can make out subtle left-lateral motion in top left of image. pic.twitter.com/cFpI4wTz4m — Chris Milliner (@Geo_GIF) July 6, 2019 Nevada Geodetic Lab (next door to M6.4, M7.1 Searles Valley quakes) is analyzing their network and other data, more here https://t.co/mnJuhMXK53 — UNAVCO (@UNAVCO) July 6, 2019 Seismologists at Scripps created this plot of the #RidgecrestEarthquake sequences and magnitudes over time. There have been more than 2,400 aftershocks to date. pic.twitter.com/mOgXQzCyz4 — Scripps Oceanography (@Scripps_Ocean) July 6, 2019 Seismologists at Scripps created this plot of the #RidgecrestEarthquake sequences and magnitudes over time. There have been more than 2,400 aftershocks to date. pic.twitter.com/mOgXQzCyz4 — Scripps Oceanography (@Scripps_Ocean) July 6, 2019 Great article by @WeiPoints in @NatGeo about the #SoCalQuake with quotes from @SeismoSue from the @USGS, Ross Stein from @temblor and me (from @IRIS_EPO). #scicomm #earthquake https://t.co/BHN0WuIMnl — Dr. Wendy Bohon (@DrWendyRocks) July 6, 2019 Satellite imagery from @Planetlabs shows surface rupture of the Mw 7.1 July 5th #earthquake. There is much larger fault slip here than the Mw 6.4, ~2m of right-lateral offset at this location (35.79, -117.61). Slip profile and correlation results to come. pic.twitter.com/RMZX9XydeM — Chris Milliner (@Geo_GIF) July 7, 2019
Well, happy fourth of July! I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1919-2019 with magnitudes M ≥ 5.0 in one version. From the USGS:
Overview of active faults and regional topography of the Eastern California shear zone (ECSZ) and southern Walker Lane belt. Labeled faults are abbreviated as follows: ALF—Airport Lake fault, BF—Blackwater fault, GF—Garlock fault, KCF—Kern Canyon fault, LLF—Little Lake fault, OVF—Owens Valley fault, SNFF—Sierra Nevada frontal fault. OL—Owens Lake, IWV—Indian Wells Valley. Major historical earthquake surface ruptures in the Eastern California shear zone and Walker Lane belt are outlined in white, with stars denoting epicentral locations: OV—1872 Owens Valley, L—Landers 1992, HM—1999 Hector Mine. Active fault traces are taken from the U.S. Geological Survey Quaternary fault and fold database, with the exception of the Kern Canyon fault, taken from Brossy et al. (2012).
Shaded relief index map of Quaternary faults, roads, towns, and fi eld trip stops in the eastern California shear zone. Most faults are from the U.S. Geological Survey Quaternary fault and fold database (http://earthquake.usgs.gov/regional/qfaults). Arrows indicate relative fault motion for strike slip faults. Bar and circle indicates the hanging wall of normal faults. Field trip stop location numbers are tied to site descriptions in the fi eld guide section. AHF—Ash Hill fault; ALF—Airport Lake fault; B—Bishop; BF—Blackwater fault; BLF—Bicycle Lake fault; BM—Black Mountains; BP—Big Pine; Br—Baker; Bw—Barstow; By—Beatty; CA—California; CF—Cady fault; CLF—Coyote Lake fault; CoF—Calico fault; CRF—Camp Rock fault; DSF—Deep Springs fault; DV-FLVF—Death Valley–Fish Lake Valley fault; EPF—Emigrant Peak fault; EV— Eureka Valley; FIF—Fort Irwin fault; FM—Funeral Mountains; GF—Garlock fault; GFL—Goldstone Lake fault; GM—Grapevine Mountains; HF—Helendale fault; HLF—Harper Lake fault; HMSVF—Hunter Mountain–Saline Valley fault; I—Independence; LF—Lenwood fault; LLF— Lavic Lake fault; LoF—Lockhart fault; LP—Lone Pine; LuF—Ludlow fault; LV—Las Vegas; M—Mojave; MF—Manix fault; NV—Nevada; O—Olancha; OL—Owens Lake; OVF—Owens Valley fault; P—Pahrump; PF—Pisgah fault; PV—Panamint Valley; PVF—Panamint Valley fault; R—Ridgecrest; S—Shoshone; SAF—San Andreas fault; SDVF—southern Death Valley fault; SLF—Stateline fault; SPLM—Silver Peak–Lone Mountain extensional complex; SNF—Sierra Nevada frontal fault; SP—Silver Peak Range; T—Tonopah; TF—Tiefort Mountain fault; TMF—Tin Mountain fault; TPF—Towne Pass fault; WMF—White Mountains fault; YM—Yucca Mountain.
Simplified geologic map of the Little Lake fault, highlighting Quaternary volcanic and alluvial deposits bearing on the Pleistocene drainage of Owens River through the Little Lake area. Map units are named and modified from Duffield and Bacon (1981). The 30 m elevation contours are taken from the National Elevation Database (NED). The 40Ar/39Ar dates are labeled as in Table 1. SNFF—Sierra Nevada frontal fault.
Northward branching of the Holocene-active Airport Lake fault zone in northern Indian Wells Valley, Rose Valley, the Coso Range, and Wild Horse Mesa. AL—Airport Lake playa; BR— basement ridge; CB—Central branch; CWF—Coso Wash fault; EB—Eastern branch; GF—geothermal field; HS— Haiwee Spring; LCF—Lower Cactus Flat; MF—McCloud Flat; UCF—Upper Centennial Flat; WB—Western branch; WHA—White Hills anticline; WHM—Wild Horse Mesa; WHMFZ— Wild Horse Mesa fault zone. Faults with especially prominent scarps in Wild Horse Mesa are highlighted in bold. Late Quaternary faults modified from Duffield and Bacon (1981) and Whitmarsh (1998), with additional original mapping. A and B indicate two faults that display evidence for late Quaternary dextral offset.
Map showing the locations of events from the SCSN Earthquake Catalog and seismic moment tensors obtained by inverting low-frequency waveforms recorded at BDSN stations CMB, PKD1, and SAO.
Seismicity (M 4 or greater) for 28 June 1992 to 1 June 1993. See Figure 1 legend for definitions of abbreviations. The 28 June 1992 Landers rupture is shown as shaded fault lines. Faults are from Jennings (1992).
Coulomb 3.3 calculation of stress transferred by the 4th July shock to the surrounding region and major faults. Here we use a simple source based on the moment tensor (geometry, sense of slip, and size) of the earthquake, as determined by the USGS.
Aerial view of a 2 km wide tension graben located along the south end of the right slip Airport Lake fault.
Map showing interpreted thickness of Cenozoic deposits and major faults outlining the deep basins, based on inversion of gravity data [56]. Connection between West Inyo and Southwest Argus faults from Pluhar et al. [58]. ALFZ = Airport Lake Fault Zone; CWF = Coso Wash Fault; EIF = East Inyo Fault; LLF = Little Lake Fault. A-A’ to H-H’ indicate lines of cross sections and gravity profiles shown in Figure 10.
Map showing deep basins, relatively shallow down-dropped blocks, extended mountain blocks, and structural zones in the ESVS, which is bounded by largely unextended mountain blocks. CB = Chalfant Basin; NBB = North Bishop Block; RVB = Round Valley Basin
Structural cross sections across the East Sierra Valley System (ESVS), with corresponding gravity profiles. Locations of sections are shown in Figure 5. No vertical exaggeration. Shading represents Quaternary sedimentary and volcanic deposits, with thicknesses based on inversion of gravity data [53].
The two beach balls show the stike-slip fault motions for the M6.4 (left) and M6.0 (right) earthquakes. Helena Buurman's primer on reading those symbols is here. pic.twitter.com/aWrrb8I9tj — AK Earthquake Center (@AKearthquake) August 15, 2018
Strike Slip: A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)
Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.
Today, on #SeismogramSaturday: what are all those strangely-named seismic phases described in seismograms from distant earthquakes? And what do they tell us about Earth’s interior? pic.twitter.com/VJ9pXJFdCy — Jackie Caplan-Auerbach (@geophysichick) February 23, 2019
Californians are real time seismometers: they jump on LastQuake app as soon as the tremor (propagating circles) reach them pic.twitter.com/ymRLUXczkc — EMSC (@LastQuake) July 4, 2019 First-motion mechanism: Mwp6.4 #earthquake Central California https://t.co/kCIw9Vypa6 https://t.co/cge7d6C4jw pic.twitter.com/iReAd4TTl4 — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 4, 2019 apparent left lateral offset along CA178 between Trona and Ridgecrest #earthquake #ridgecrest pic.twitter.com/tjZagKMJ9V — Ian Pierce (@neotectonic) July 4, 2019 Southern California M 6.4 earthquake stressed by two large historic ruptures | https://t.co/1twVj9WIVY https://t.co/bvNUbcEbPG via @temblor #SouthernCalifornia #earthquake #LA — temblor (@temblor) July 4, 2019 this is over by Trona pic.twitter.com/6SXodtcQ8z — t.s. idiot (@THEjoeydavis) July 4, 2019 Here's a map of focal mechanisms for the M 6.4 Searles Valley sequence. Mostly strike-slip and the outliers will probably get cleaned up by analysts in coming days. pic.twitter.com/UfKxszbNF7 — Zach Ross (@zross_) July 5, 2019 BREAKING: Video footage shows a landslide following a magnitude 6.6 #earthquake in Southern California. — Global News Network (@GlobalNews77) July 4, 2019 Also while talking about the Searles Valley #Earthquake today @GriffithObserv’s seismograph detected and recorded an aftershock: a 4.0 at 1634PDT/2334UTC. pic.twitter.com/KzkOubP8hQ — THE MONTH OF GAY WRATH HAS BEGUN 💪✊👊🏳️🌈 (@jaredhead) July 5, 2019 ❗️NEW VIDEOS ❗️@USGS reported that 6.4 magnitude #earthquake rocked Ridgecrest, California at 10:33am Pacific Time. The earthquake was also felt in Los Angeles, #California.#CAwx pic.twitter.com/qHpLlP6HXB — WeatherNation (@WeatherNation) July 4, 2019 "We should be expecting lots of aftershocks and some of them will be bigger than the 3s we've been having so far," says USGS seismologist Lucy Jones on the California quake. "I think the chance of having a magnitude 5…it's probably greater than 50-50." https://t.co/klvvgQkSCI pic.twitter.com/oMAHheAsic — CNN (@CNN) July 4, 2019 THREAD: A strong (Mw 6.4) earthquake occurred 12 km SW of Searles Valley, — USGS (@USGS) July 4, 2019 To all heading to the ridgecrest earthquake rupture zone: please, please do not trespass on the military base. This includes drone overflights! Trespassing could result in loss of access permission for everyone. Don’t be that person. — Mike Oskin (@mikeoskin) July 5, 2019 I collected a few links and mashed up a couple of graphics to help think about the #earthquake in southeastern California: https://t.co/u0qJCX9SP9 — Ramon Arrowsmith (@ramonarrowsmith) July 4, 2019 Pictures my mom took while working out in ridgecrest… pic.twitter.com/aLRBwMB2jm — Em💞 (@Emily31377) July 4, 2019 Rupture says hi (probably a zone of distributed opening and rotation, most likely, the 'ruptures' are oriented N-S which is very oblique to the strike) pic.twitter.com/jWbFTEvhuj — Gareth Funning (@gfun) July 5, 2019 Watch the waves from the M6.4 southern California #earthquake roll across the USArray seismic network (https://t.co/RIcNz4bgWq)! #socalearthquake THREAD pic.twitter.com/RUcTkh4cHF — IRIS Earthquake Sci (@IRIS_EPO) July 5, 2019 6.4 magnitude earthquake hits Southern #California — Trama (@Trama70602212) July 4, 2019 6.4 magnitude earthquake hits Southern #California — Trama (@Trama70602212) July 4, 2019 California’s joint Emergency Management Team @Cal_OES @CHP_HQ @CAL_FIRE @theCaGuard joining @kerncountyfire on a damage assessment overflight of the #RidgecrestEarthquake #OneTeamOneFight #MACS #ICS #SEMS pic.twitter.com/mKExsN2r7Y — mark s ghilarducci (@CalOES_Dir) July 5, 2019 Ridgecrest Regional Hospital being evacuated. #ABC7Eyewitness #Ridgecrest #RidgecrestEarthquake #KernCounty #SearlesValley .@cnnbrk .@CNN .@ABC7 .@CBSLA .@cbs2kcal9brk pic.twitter.com/g5kFnKQzDI — Go Ridgecrest – Tourism & Filming – RACVB (@goridgecrest) July 4, 2019 California M6.4 earthquake: for examples of past ruptures on conjugate faults see summary in Fukuyama (2015 https://t.co/SwSSJ35RQM) https://t.co/VwHHW2OUcR pic.twitter.com/RSLj41loqv — Pablo Ampuero (@DocTerremoto) July 5, 2019 The morning after the evening before… No offset in the paint line across the asphalt repairs => probably no significant ongoing shallow afterslip at this location. pic.twitter.com/XxNRiNdEr0 — Gareth Funning (@gfun) July 5, 2019 UPDATE to previous tweet https://t.co/HcDzaWnNce Thanks to @gfun: accurate location of road offset 35.644050°N 117.536939°W I haven't realised former field photo was taken with long focal lens. At the right site, even the black mark is visible on google street view 🤓 pic.twitter.com/CDqBiA2OKK — Robin Lacassin (@RLacassin) July 5, 2019 A large-ish quake (6.4M) just shook Southern California. I'll be continuously updating this post as information comes in for @ForbesScience, which will explain: — Dr Robin George Andrews 🌋 (@SquigglyVolcano) July 4, 2019 My dad lives in Ridgecrest and felt strong ground shaking. I asked him to take pictures of any damage, see photos below (credit Adam Graehl). M 6.4 – 12km SW of Searles Valley, CAhttps://t.co/3e222a3nq8 pic.twitter.com/jaTt3GWLYw — Nick Graehl (@nickgraehl) July 4, 2019 Surface rupture near Ridgecrest! pic.twitter.com/JsFlLGieSG — Danielle Madugo (@DanielleVerdugo) July 5, 2019 These are my rapid coseismic values for the Searles Valley EQ. Using about 100 seconds on either side of the shaking. @UNAVCO pic.twitter.com/i8ChP2x0Sp — Brendan Crowell (@bwcphd) July 5, 2019 About 100 ft wide zone of parallel ruptures showing LL and some dilation along the Ridgecrest surface rupture. pic.twitter.com/Gp5a1G0tG6 — Danielle Madugo (@DanielleVerdugo) July 5, 2019 A "reminder that the Big One lurks." "Lurks" might be an under-used word in earthquake #SciComm. A good word. @NickAtNews https://t.co/fi1Zj2qSo2 — Susan Hough (@SeismoSue) July 5, 2019 #Ridgecrest #Earthquake: M5.4 aftershock 2019-07-05 11:07 UTC (below) and M6.4 mainshock (above) seismograms plotted with the same amplitude scale. — Anthony Lomax 🌍🇪🇺 (@ALomaxNet) July 5, 2019 More surface ruptures from #RidgecrestEarthquake #earthquake #Ridgecrest with @faultcreeper pic.twitter.com/iPjV1cXo63 — Ian Pierce (@neotectonic) July 5, 2019
Earthquake Report: Ridgecrest Update #2
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.Field Work Narrative
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
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
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.
NASA JPL ARIA Data Products
Dr. Sotiris Valkaniotis
PBS News Hour: 2019.07.08
Death Valley at Devil’s Hole
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
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!
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
Field Photos
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
Southern CA
Earthquake Reports
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@patton_cascadia@FaultyAndSalty#RidgecrestEarthquake https://t.co/kkDR4WP2ib
M≥2.0 2019-07-04>2019-07-10-09h https://t.co/sRUqn89xEO relocations w/ station corrections, over ALOS-2/JAXA/@NASAJPL-ARIA interferogram https://t.co/NpRQTwvQn8
Events colored by origin time before & after M7 mainshock (left), & by depth (right) pic.twitter.com/GnOO4kYR0K
Red = secondary faults
Blue dots = aftershocks (SCSN) pic.twitter.com/N3TSO02GYA
This one woke me up:
The path has just begun.@SimoneAtzori73 @maferp_13 @FraxInSAR @EugenioSansosti pic.twitter.com/F34nIjfZKL
M6.4 2019-07-04 (green)
M7 2019-07-06 (black)
…and many, many aftershocks#Australia
M6.6 2019-07-14 (blue, lower left, 06h)#Indonesia
M7.3 2019-07-14 (blue, lower right) pic.twitter.com/vxnqPB8zd6
"S041 – The 2019 M6.4 Searles Valley and M7.1 Ridgecrest Earthquakes"
Some improvement…https://t.co/adGovA3GyP
Visit https://t.co/umhIv4gJkU for more information about the earthquake pic.twitter.com/vxCY9663om
Quite possibly the best animations on this sequence.
References:
Return to the Earthquake Reports page.
Earthquake Report: Halmahera, Indonesia
I was just about done with these new maps and getting ready to start writing them up in an updated earthquake report when I noticed that there was an interesting earthquake, with few historic analogues, along the Western Australia Shear Zone offshore of northwestern Australia. I probably won’t get to that earthquake, but I started downloading some material and reviewing my literature for the region. I considered doing both of these tasks on Sunday (today). That was not to be as I awakened to an email about this magnitude M 7.3 earthquake in Halmahera, Indonesia. I have several earthquake reports for the Molucca Strait, west of Halmahera. So, I have some background literature and knowledge about this region already.
There was an earthquake along Molucca Strait that I could not work on due to my field work. So I will briefly mention that quake here. There was also a recent earthquake to the south, in the Banda Sea (here is my earthquake report for that event). The June earthquake had the same magnitude as today’s shaker, M = 7.3. However, the earlier quake was too deep to cause a tsunami (unlike today’s temblor). Earthquakes along the Molucca Strait have generated tsunami with wave heights of over 9 meters (30 feet) according toe Harris and Major, 2016.
https://earthquake.usgs.gov/earthquakes/eventpage/us70004jyv/executive
The Molucca Strait is a north-south oriented seaway formed by opposing subduction zone / thrust faults (convergent plate boundaries). See the “Geologic Fundamentals” section below for an explanation of different fault types. On the west of the Molucca Strait is a thrust fault that dips downwards to the west. On the east, there is a thrust fault that dips down to the east (beneath the island of Halmahera).
There is a major east-west trending (striking) strike-slip fault that comes into the region from the east, called the Sorong fault. There are multiple strands of this system. A splay of this Sorong fault splays northwards through the island of Halmahera. There may be additional details about how this splay relates to the Sorong fault, but I was unable to locate any references (or read the details) today. According to BMKG, the fault that is associated with this earthquake is the Sorong-Bacan fault.
Today’s M 7.3 Halmahera earthquake is a strike-slip earthquake (the plates move side-by-side, like the San Andreas or North Anatolia faults). Often people don’t think of tsunami when a strike-slip earthquake happens because there is often little vertical ground motion. Many people are otherwise familiar with thrust or subduction zone earthquakes, which can produce significant uplift and subsidence (vertical land motion), that can lead to significant tsunami.
However, there is abundant evidence that strike-slip earthquakes do cause tsunami, though often of much smaller size than their thrust/subduction siblings. The main difference is that these strike-slip generated tsunami are much smaller in size.
For example, the 1999 Izmit and 2012 Wharton Basin earthquakes provided empirical evidence of strike-slip earthquake triggered tsunami. More recently, the 28 September 2018 magnitude M 7.5 Dongalla-Palu earthquake caused a tsunami in Palu Bay, Sulawesi, Indonesia that exceeded 10 meters (33 feet) in wave height (wave run up elevation)!!! I just got an email from Dr. Lori Dengler who is an a conference where people claim that the earthquake is possibly singlehandedly responsible for this large wave. Previously people thought that there may have been submarine landslides that contributed to the size.
Here is the tide gage record from a gage near today’s M 7.3 earthquake. The earthquake epicenter appears to be on land, so the tsunami is possibly smaller because of this. Indonesia operates a network of tide gages throughout the region here. The gage data below are from the island of Gebe, about 50 miles to the east of the M 7.3 epicenter.
Here is a quote from the Meteorology, Climatology and Geophysics Agency (BMKG) website:
Based on community reports, it was shown that shocks were felt in Bitung and Manado with the intensity of IV-V MMI (felt by almost all residents, many people built), and in Ternate III-IV MMI (felt by many people in the house). Until now there have been no reports of damage due to a strong earthquake shock in northern Maluku last night. The impact of the North Maluku earthquake only caused a tremendous panic among the people. In the city of Manado, some of the houses of the walls had cracks in the building walls of the building with very light categories.
Below is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange). Due to the high rate of seismicity in this region, I do not have an historic seismicity poster for this event.
Magnetic Anomalies
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Other Report Pages
Shaking Intensity and Potential for Ground Failure
Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.
Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.
Here is a map with landslide probability on it (Jessee et al., 2017). 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)
Here is a map showing liquefaction susceptibility (Zhu et al., 2017).
Seismic Hazard and Seismic Risk
Tsunami Hazard
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
Philippines | Western Pacific
Earthquake Reports
Social Media
Run-up of ~1 m possible around epicenter @ShakingEarth pic.twitter.com/uUHBuf3QkY
References:
Return to the Earthquake Reports page.
Earthquake Report: Ridgecrest Update #1
Last night there was the largest aftershock (so far) a magnitude M 5.4 earthquake.
It is clear that this sequence has involved at least 2 main faults. I interpret the mainshock (the M 6.4) to be on a northeast trending (striking) left-lateral strike-slip fault. This is largely because (1) the longer of the 2 aftershock trends is has this orientation and (2) the majority of field observations of surface rupture are along this orientation. The M 5.4 aftershock is located along the right-lateral northwest trending fault. The M 6.4 could be on the nw striking fault.
Lots of information about the regional tectonics is in my original report, so I won’t rehash that here.
Seismicity Visualization
Updated Seismicity Map
LATE BREAKING NEWS
UPDATE
UPDATE: 2019.07.06 afternoon
Other Report Pages
USGS Earthquake Forecast (UPDATED 5 July 2019)
Be ready for more earthquakes
About this earthquake and related aftershocks
What we think will happen next
About our earthquake forecasts
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
Southern CA
Earthquake Reports
Social Media
M7.1 succeeding aftershocks are 1.4x larger in numbers and, so far, released 6.5x more energy than aftershocks succeeding the M6.4 event two days ago (within ~4h)
UPDATE: 2019.07.06
Wating for #InSAR measurements.#RidgecrestEarthquake #TerremotoCalifornia #Terremoto @InSARinfo @USGSBigQuakes @EricFielding @gfun pic.twitter.com/jCXsE9oqL5
Screenshot from NGL webpage pic.twitter.com/LFM5Mz3OLj
UPDATE: 2019.07.07
References:
Return to the Earthquake Reports page.
Earthquake Report: Ridgecrest, CA
There was a good sized earthquake in southern California today. The largest earthquake since the 1999 M 7.1 Hector Mine earthquake. (The 2003 San Simeon earthquake was larger, but much farther to the west, at about the same latitude.)
Today’s earthquake sequence has a mainshock (so far) with a magnitude M = 6.4. If you live in southern California or southern Nevada, please visit this website to describe your observations.
https://earthquake.usgs.gov/earthquakes/eventpage/ci38443183/executive
This region is at the intersection of several different fault systems. The Pacific-North America plate boundary, which most people associate with the San Andreas fault, includes the South Sierra Nevada fault zone and other right-lateral strike-slip faults that trend along the eastern side of the Sierra Nevada Mountains (including the Eastern California Shear Zone). There is also an interesting conjugate fault, the Garlock fault, which is a left-lateral strike-slip fault.
If we zoom into the area where this earthquake sequence is happening, we can locate some mapped faults. Some are parallel to the S. Sierra Nevada system and some are parallel to the Garlock fault. The faults parallel to the Sierra Nevada system are right-lateral and the faults parallel to the Garlock are left-lateral.
The sequence today appears to involve faults with both orientations. Looking at the aftershocks, it looks like the main shock is left-lateral (more aftershocks along the northeast trend).
These strike-slip faults also have normal motion on them (so they are both strike-slip and normal, i.e. “oblique”).
There are photographic reports of surface rupture (where the earthquake fault breaks the ground surface) across Highway 178.
This earthquake will be studied over the coming weeks, so I will be preparing updates in the near and far future.
The USGS earthquake products I review below include (1) the probability (“chance for”) landslides and liquefaction and (2) an earthquake forecast (the chance of future earthquakes for given time ranges).
Below, check out the social media links. There are field observations and a link to a Temblor report where they suggest this earthquake was possibly triggered by earthquakes in the 20th century.
Here is the Baby Benioff Seismograph from Humboldt State University, Department of Geology (photo credit Dr. Mark Hemphill-Haley).
This is in a tweet below, but the figure is so telling, I am placing it up here. Some may need to read more background material (below) to understand this figure.
This figure shows earthquake mechanisms (focal mechanisms) for seismicity associated with this ongoing sequence in Ridgecrest.
There are lots of great field photos in tweets below. Here is one of them. The reason I show this here is to mention one of the principles of geologic time. Relative time is based on several principles (e.g. law of superposition, principle of original horizontality). The principle demonstrated here is cross cutting relations.
The spectacular example spans different time scales. First the road was built, then the paint stripes were painted (superposed above the road, so are younger than the road). Then the driver of the Jeep felt the earthquake (inferred by the black rubber skid marks). The skid marks were then offset by the earthquake (the skid marks are cross-cut by the earthquake fault).
This objective information tells us several things about the earthquake. I already mentioned that the driver may have felt the earthquake, leading them to skid to a stop. The cool thing is that we can tell that the fault slipped in this area after the person skid across the fault. This is really cool… at this location, the shaking started prior to the fault slip.
UPDATE: Ian Pierce tells us that the black mark is not a skid mark, but road tar. So, I was incorrect.
UPDATE (2019.07.05): Here is my first Earthquake Report UpdateBelow is my interpretive poster for this earthquake
I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
Global Strain
I include some inset figures. Some of the same figures are located in different places on the larger scale map below.
Landslide, Liquefaction, and Shaking Intensity
USGS Earthquake Forecast (UPDATED 5 July 2019)
Be ready for more earthquakes
About this earthquake and related aftershocks
What we think will happen next
About our earthquake forecasts
Other Reports for this Earthquake
Some Relevant Discussion and Figures
Geologic Fundamentals
Compressional:
Extensional:
San Andreas fault
General Overview
Earthquake Reports
Northern CA
Central CA
Southern CA
Eastern CA
Southern CA
Earthquake Reports
Social Media
pic.twitter.com/vGtflE7ScQ
California on the China Lake Naval Air Center at 10:33:48 am local
time on July 4, 2019. The closest big population center is the city of
Ridgecrest with a population of 28k people.
Check out the skid marks:
Firefighters working fire pic.twitter.com/iv80v2Q5aZ
Firefighters working fire pic.twitter.com/iv80v2Q5aZ
UPDATE: 2019.07.05
-What caused it
-What this quake *isn't* related to
-How this fits in with the region's geologyhttps://t.co/BRLCSihyUH
Seismic station at Goldstone ~80km SE of the epicenters. pic.twitter.com/or445gJzPw
References:
Return to the Earthquake Reports page.