The first main shock (now deemed to be a foreshock) occurred on Thursday, July 4 at 10:33 a.m. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona,[9] on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone.

Relatively minor damage resulted from the initial foreshock, though some building fires were reported in Ridgecrest near the epicenter.

[14] At 10:02 a.m. PDT (17:02 UTC) on July 4, 2019, a 4.0 Mw  foreshock occurred about 6.8 mi (10.9 km) southwest of Searles Valley, California.

[15][16] A foreshock registering 6.4 Mw  occurred at 10:33 a.m. PDT (17:33 UTC) 7.5 mi (12.1 km) southwest of Searles Valley.

[18] 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.

[21] Focused at a relatively shallow depth of 6.6 mi (10.7 km), the foreshock affected a large region populated by 20 million people.

[24] A significant series of additional earthquakes followed the foreshock, with the majority of magnitudes ranging approximately 2–4 Mw .

[27] Shaking from this aftershock was felt as far north as Fresno, as far south as Laguna Hills (including Los Angeles), and as far east as Las Vegas, Nevada.

[30] On June 3, 2020, at 6:32 PM PST, a 5.5 Mw  aftershock was recorded 11 miles south of Searles Valley.

[18] Fifteen patients at Ridgecrest Regional Hospital and residents in several apartment buildings were evacuated.

[28] In Los Angeles proper, power outages affected the Fashion District and Granada Hills.

[5][6] Hours after the Mw  6.4 foreshock, California Governor Gavin Newsom approved an emergency proclamation for Kern County.

[74][75] Local emergency responders such as the Los Angeles Police Department used social media to alert the public that they were aware of the earthquake and to only use 9-1-1 if there was dangerous conditions or injuries.

[67] Naval Air Weapons Station China Lake brought in additional personnel to conduct damage assessments.

Due to temperatures exceeding 100 °F (38 °C), Cal OES established cooling stations in the affected areas.

[83] ShakeAlertLA is triggered by the ShakeAlert system being developed by the USGS that monitors earthquakes across Southern California.

[88][89] The broad context of the Ridgecrest earthquakes is the Eastern California Shear Zone (ECSZ), a seismically active region east of the southern segment of the San Andreas Fault (SAF) and largely coincident with the Mojave Desert, featuring multiple right-lateral strike-slip faults paralleling the SAF.

The OVF runs south, largely along U.S. Highway 395, through Bishop, Big Pine, Independence, and Lone Pine to the northern end of Rose Valley and the northwestern corner of the Naval Weapons Center (NWC), where the OVF turns slightly to the east.

[105] Geodetic measurements show that the slip-rate of Garlock Fault is currently less than half of its estimated long-term geological rate.

The Owens Valley quake is believed to be the greatest earthquake on record and not just for California, but also for the western continental United States.

[115] In March 1946 an ML 6.3[116] earthquake struck near Walker Pass (crest of the Sierra Nevada, due west from Ridgecest), with aftershocks continuing for nearly a year.

[113] Following the Landers earthquake "a well-developed linear pattern of primary and triggered aftershocks" was observed that extended along the Little Lake Fault and into Owens Valley.

[129] Seismicity in Indian Wells Valley has been characterized by swarms of thousands of earthquakes, some lasting for more than a year.

[132] An earlier study[133] noted that successive earthquake sequences here tend to increase in number and magnitude, and migrate southward.