The 2019 Ridgecrest Earthquake Sequence
The M7.1 mainshock of the Ridgecrest Earthquake Sequence struck at 03:19 UTC on 6 July 2019 at a depth of 8.0 km. This event occurred directly within the Ridgecrest area of Kern County, California, and stands as the sole strong earthquake (M7.0 or greater) recorded in the region since 1 January 2000. The Ridgecrest area lies in the western Mojave Desert, where the crust accommodates right-lateral shear between the Pacific and North American plates. The sequence ruptured within the Little Lake Fault Zone, a network of northwest-trending strike-slip faults that connect the Garlock Fault to the south with the Owens Valley Fault system to the north. Regional geology features Precambrian to Mesozoic basement rocks overlain by Quaternary alluvial and lacustrine sediments that fill fault-bounded basins. These young deposits amplify ground motion during earthquakes and record long-term slip rates of several millimeters per year on nearby faults. Seismicity in the Mojave block has been monitored continuously since the early twentieth century. Prior to 2019, the largest event since 2000 remained well below M7.0, consistent with the data provided. The 2019 sequence released strain accumulated along the Little Lake Fault Zone and triggered widespread aftershock activity that illuminated previously unmapped fault strands. Post-event studies refined fault-slip models and confirmed that the mainshock produced surface rupture exceeding 50 km in length, with maximum right-lateral offsets near 5 m. Current hazard assessments for the region incorporate the 2019 observations to update recurrence intervals on the Garlock and Little Lake faults. These models indicate that the Mojave Desert remains capable of producing M7+ events, underscoring the importance of continued seismic monitoring and resilient infrastructure design in eastern California.
References
USGS Earthquake Catalog (event parameters and regional seismicity since 2000)
California Geological Survey, Fault Activity Map of California (geologic setting and fault zones)