All three earthquakes have been described by the United States Geological Survey as occurring via shallow strike-slip mechanisms. PDT on July 5, a larger 7.1 M w earthquake occurred in the Ridgecrest area after being preceded by a 5.0 M w foreshock 3 minutes prior, revealing the previous day's 6.4 M w earthquake to have been a foreshock. Shaking was felt as far north as Sacramento, California, eastward to Phoenix, Arizona, and as far south as Baja California, Mexico, with evacuations taking place in Mexicali and Tijuana. Residents near the epicenter reported that shaking lasted approximately 30 seconds. Focused at a relatively shallow depth of 6.6 mi (10.7 km), the foreshock affected a large region populated by 20 million people. The exact fault it occurred on is uncertain with many small faults encompassing the region, though United States Geological Survey (USGS) seismologist Susan Hough stated it may have been the Little Lake Fault. Earth on either side of the fault was deformed, with lateral shifts of 6–8 in (15–20 cm) in the immediate vicinity. The rupture occurred along a 10 mi (16 km) section of an unspecified fault. The foreshock originated along a strike-slip fault in the Eastern California Shear Zone, a region frequented by earthquake swarms, near the edge of Death Valley National Park. The most populated area near the epicenter was Ridgecrest, home to 28,000 people. A foreshock registering 6.4 M w occurred at 10:33 a.m. PDT (17:02 UTC) on July 4, 2019, a 4.0 M w foreshock occurred about 6.8 mi (10.9 km) southwest of Searles Valley, California.
The red dot marks the M 7.1 event.Īt 10:02 a.m. The July 4 M 6.4 event (orange dot) occurred on the SW-NE fault where it intersects the NW-SE oriented fault. The aftershocks of the Ridgecrest earthquakes reveal two fault zones. An estimated 20 million people experienced the foreshock, and approximately 30 million people experienced the mainshock. Effects were felt across much of Southern California, parts of Arizona and Nevada, as far north as the San Francisco Bay Area and Sacramento, and as far south as Baja California, Mexico. The main quake on July 5 cut power to at least 3,000 residents in Ridgecrest. Relatively minor damage resulted from the initial foreshock, though some building fires were reported in Ridgecrest near the epicenter. Subsequent aftershocks extended approximately 50 km (~30 miles) along the Little Lake Fault Zone. The latter, now considered the mainshock, was the most powerful earthquake to occur in the state in 20 years (after the 1999 Hector Mine earthquake). PDT approximately 10 km (6 miles) to the northwest. The M 5.4 and M 7.1 quakes struck on Friday, July 5 at 4:08 a.m.
This quake was preceded by several smaller earthquakes, and was followed by more than 1,400 detected aftershocks. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona, on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone. The first main shock (now deemed to be a foreshock) occurred on Thursday, July 4 at 10:33 a.m. Eleven months later, a M w 5.5 aftershock took place (the largest aftershock of the sequence) to the east of Ridgecrest. They included three initial main shocks of M w magnitudes 6.4, 5.4, and 7.1, and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. The 2019 Ridgecrest earthquakes (more commonly referred to in scientific literature as the 2019 Ridgecrest earthquake sequence) of July 4 and 5 occurred north and northeast of the town of Ridgecrest, California located in Kern County and west of Searles Valley (approximately 200 km north-northeast of Los Angeles).
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