Strong magnitude 6 quake strikes in Antelope Valley near California-Nevada border, no significant damage reported
Locaion of user reports feeling this morning's quake in California

Early morning on 8 July 2021, a strong magnitude 6.0 earthquake struck Little Antelope Valley, California at 3:49pm local time (July 8 at 22:49 UTC). The quake was registered at shallow depth of around 6 miles (9.8 kilometers) only.

The epicenter was about 20 miles southwest of Smith Valley, NV. Perceived shaking for the quake was very strong near the epicenter and light shaking could be felt in up to hundreds of miles distance, including the SF Bay area and Las Vegas. Within minutes, hundreds of users sent reports of shaking to our monitoring service. So far, USGS has received more than 20,000 reports for this quake.



There were no immediate reports of serious damage or injuries, fortunately. Near the epicenter, things fell off shelves, windows were broken, weak walls and some roofs were damaged. Rockfalls occurred on highways near mountain slopes, with rocks hitting cars. According to local news, people were not injured.





The shaking lasted for 30 seconds or more, and people ran out of buildings.



Initial report of magnitude 4.8

Initial calculations had indicated two earthquakes striking 25 seconds but 100 miles (161 kilometers) apart. After a review, USGS removed the magnitude 4.8 quake in Farmington, about five miles (8 km) southeast of Stockton. The uncertainty was caused by the remote location, which had fewer seismic instruments, Austin Elliott, a USGS geologist, explained to ABC news: “The system underestimated the original magnitude of that event and estimated a location that was slightly off from the true location,” he said.

As the seismic waves moved across the state, other stations misinterpreted them as a separate quake because ”they arrived at an unexpected time," Elliott said.

Elliott also said earthquakes commonly happen along this fault. He cited a magnitude 5.8 earthquake that rattled the Eastern Sierra town of Lone Pine last month and sent boulders crashing down Mt. Whitney.



Aftershocks

Less than a minute later, a strong aftershock of magnitude 5.2 occurred in the area and nearly 100 smaller aftershocks occurred during the 8 hours since the quake, reaching magnitudes of up to 4.6. These will continue in the near future, but decrease with time.



Tectonic information

The quake occurred as the result of normal faulting in the shallow crust of the North America plate. Preliminary focal mechanism solutions for the event, which describe the style of faulting in an earthquake, indicate slip likely occurred on a moderately dipping fault striking roughly north-south. This motion is consistent with east-west oriented extension that is common in Nevada and eastern California. This earthquake occurred along the eastern edge of the Sierra Nevada, a major physiographic boundary along the California-Nevada border.



Tectonically, this event occurred at the margin of the stable Sierra Nevada microplate and the Walker Lane, a zone of distributed shear. The Sierra Nevada microplate moves at about 12 mm/yr to the northwest relative to the North American plate. The Sierra Nevada microplate is a part of the broader Pacific-North America plate boundary system of California, and roughly 25% of the 5 cm/yr total plate boundary motion occurs east of the Sierra Nevada. Earthquakes in the vicinity of the July 8 earthquake include both normal faulting earthquakes and strike-slip earthquakes.



In the past 100 years, 33 earthquakes of M5+ or larger have occurred within 100 km of the July 8 earthquake. The largest of these were a M6.1 earthquake 36 km to the northwest in September 1994 and a M6.1 earthquake 63 km to the north in June 1933.



Source: USGS

Earthquake data:
Date & time: 8 Jul 3:49 pm (GMT -7) local time (8 Jul 2021 22:49 GMT)
Magnitude: 6.0
Depth: 7.5 km
Epicenterlatitude / longitude: 38.51°N / 119.5°W (Mono, California, United States)
Primary data source: USGS
https://www.volcanodiscovery.com/earthquake/news/134902/Strong-magnitude-6-quake-strikes-in-Antelope-Valley-near-California-Nevada-border-no-significant-dam.html