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July 2020: Ridgecrest Earthquake First Anniversary
- From the Director
- Science Highlights
- Other Stories in the News
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The Ridgecrest earthquake sequence – one year later
 The Ridgecrest earthquake sequence that started a year ago at the southern end of the Walker Lane provided clear reminders that (i) potentially damaging large earthquakes occur in Southern California on timescale of decades and (ii) up close views reveal important features not accounted for by current understanding of accumulation and release of seismic energy. The recent June 4, 2020, M5.5 aftershock at the southern end of the 2019 Ridgecrest rupture, and the June 24, 2020, M5.8 earthquake near Lone Pine (also likely part of the Ridgecrest sequence) illustrate the complex nature of earthquakes interactions in space and time.
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Earthquake geology and the Ridgecrest earthquake
 Most SCEC scientists were preparing for 4th of July celebrations when the M6.4 Ridgecrest earthquake occurred. Numerous industry, academic, and agency geologists responded quickly to capture ephemeral data, following earthquake rapid response protocols developed with SCEC participation. Earthquake geology observations included documentation of offsets and mapping of the complex ground ruptures, as well as fragile geologic features that constrained strong ground motions. Field observations were augmented with remote mapping technology including high-resolution photogrammetry, airborne and terrestrial laser scanning, and image and topographic differencing.
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How the Ridgecrest earthquake sequence unfolded
 In July 2019 southern California was shaken by the largest quake to occur in the past twenty years, a M7.1 earthquake located near Ridgecrest, California. This was also the first major earthquake since the start of the modern era of the Southern California Seismic Network, which resulted in recording some of the densest and highest quality data of any large earthquake to occur in the United States. Seismologists supplemented these data with hundreds of additional temporary seismic instruments that were installed in the days following the earthquake. In the year since the sequence began, researchers have been using the seismic data to peer into the Earth to identify which faults moved, and when.
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Operational aftershock forecasting during the Ridgecrest sequence
 The 2019 Ridgecrest earthquake sequence was the first significant ‘real-world’ application of the Third Uniform California Earthquake Rupture Forecast with Epidemic Type Aftershock Sequences (UCERF3-ETAS) model in the California forecasting region since it was released in 2017. For the one-year anniversary of the 2019 Ridgecrest sequence, we share our experiences and responsibilities as SCEC researchers as this sequence unfolded, and what we’ve learned since that has resulted in numerous operational improvements and the first “out of sample” evaluation of the UCERF3-ETAS model.
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Lessons from the 2019 Ridgecrest earthquakes: a geodetic perspective
 The 2019 M7.1 Ridgecrest earthquake was the third major earthquake to occur in the Eastern California Shear Zone since the advent of satellite space geodesy in the 1970's and 1980’s. These events exemplify how high quality geodetic data can provide new insights into earthquake processes. The Ridgecrest earthquakes (M7.1 mainshock and its M6.4 foreshock) were imaged by multiple radar satellite missions, including Sentinel-1A/B, ALOS-2, and COSMO-SkyMed, and data was collected from campaign GNSS surveys. Early data processing results were shared with teams working in the field in near real time, and were used to identify and map additional surface ruptures and measure coseismic slip.
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Imaging the Ridgecrest earthquake ruptures from drones to space
 The 2019 Ridgecrest earthquake sequence occurred on two orthogonal faults, rupturing the surface in a complex pattern that included surface cracking, fault splays, and stepovers. The extent of surface rupture in an arid region and the availability of new optical imaging platforms made it possible to image the ruptures, associated surface cracking, and surface change spanning the earthquake sequence. We used small Uninhabited Aerial Vehicles (sUAS) or drones to target specific areas after the earthquake and commercial spaceborne imagery to measure the entire ruptures and separate deformation from the M6.4 and M7.1 earthquakes. We are continuing drone imaging of the area to search for longer term postseismic motions. The imagery proved useful for identifying surface cracking and guiding field observations.
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Damage to fragile geological features from the 2019 M7.1 Ridgecrest earthquake
 Understanding the upper limits of ground motions is key to designing critical infrastructures that have long lifespans and need to withstand extreme ground shaking from large earthquakes. But unfortunately the short history of seismic instrumentation is only a fraction of the recurrence interval of large earthquakes. However, we can rely on Fragile Geological Features (FGFs) to constrain the upper limits of ground motions in the absence of instruments. Precariously balanced rocks (PBRs), a type of FGF, have been used in the past to provide estimates of ground motions a region has experienced. The observation of damaged versus undamaged PBRs following earthquakes is critical in calibrating and validating PBR ground motion assessment methodologies developed from lab experiments and numerical modeling.
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Earthquake Science
07/05/2019: A 6.4-magnitude earthquake shook California. Now comes the ‘swarm’ of Aftershocks (Washington Post)
07/05/2019: Hundreds of aftershocks follow Ridgecrest earthquake, California's strongest in 20 years (USA Today)
07/05/2019: 11% chance of another huge earthquake in Southern California, scientists say (LA Times)
07/09/2019: Expect 34,000 aftershocks from Ridgecrest earthquakes. But seismic activity is slowing down (LA Times)
07/09/2019: The Ridgecrest earthquakes: Torn ground, nested foreshocks, Garlock shocks, and Temblor’s forecast (Temblor)
07/10/2019: Ridgecrest Earthquake Sequence: Activities and Results So Far (SCEC.org)
07/23/2019: More than 80,000 aftershocks and counting: Ridgecrest earthquakes keep shaking (LA Times)
07/23/2019: Watch the Ridgecrest Earthquake Shatter the Desert Floor (LA Times)
08/30/2019: Ridgecrest earthquake shut down cross-fault aftershocks (Temblor)
09/30/2019: Could the M7.1 Ridgecrest, CA Earthquake Sequence Trigger a Large Earthquake Nearby? (USGS)
10/17/2019: Analysis of recent Ridgecrest, California earthquake sequence reveals complex, damaging fault systems (Science Daily)
10/18/2019: New Movement Along Garlock Fault Line In California Could Mean Bigger Earthquakes (NPR)
10/19/2019: A California fault capable of producing a magnitude 8 earthquake has started 'creeping.' It's not the only one (Business Insider)
12/11/2019: Scientists Scramble to Collect Data After Ridgecrest Earthquakes (AGU Eos)
5/11/2020: Seismic hazard increased following 2019 Ridgecrest event (Temblor)
06/03/2020: Yes, The 5.5 Earthquake You Felt Was A Ridgecrest Aftershock (LAist)
06/03/2020: M 5.5 Ridgecrest aftershock (Temblor)
06/03/2020: M5.5 near Searles Valley (SCSN.org)
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