M 6.0 - Antelope Valley, CA

Tectonic Summary

The July 8, 2021 M 6.0 earthquake in Antelope Valley, California, 32 km south-southwest of Smith Valley, Nevada, 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.