M5.1 - SOUTHERN CALIFORNIA

Tectonic Summary

A M5.1 earthquake occurred at 8:18 PM PDT, 16 miles WNW of Ludlow, CA. This earthquake was felt throughout the Mojave and weakly felt by many in the LosAngeles region. It was reported felt as far away as Kingman, AZ to the east, Camarillo to the west, and El Centro to the south. It was located near the NW extension of the Pisgah fault , near the NW terminus of the 1999 Hector Mine earthquake, and at the edge of a cluster of off-fault Hector Mine aftershocks. The hypocenter was located approximately 5.9 km (3.7 miles) deep.

The focal mechanism is consistent with right-lateral strike-slip on a N-NW trending MSZ fault, or left-lateral slip on a cross-fault. The mainshock was followed by a sparse aftershock sequence that included 30 recorded events in the first 36 hours, the largest of which was a M2.8 approximately 10 hours after the mainshock. The aftershock activity rate is about 50% of the average for a M5.1 mainshock in California.

The aftershocks indicate a N-NW trend, suggesting that the mainshock occurred on an unmapped extension of the Lavic Lake fault. No surface rupture is expected given the magnitude and depth of the event. The Lavic Lake fault is one of the N-NW trending strike-slip faults in the Mojave Shear Zone. Faults in this zone have been active in recent decades, producing the M7.3 Landers earthquake on 28 June 1992 as well as the M7.1 Hector Mine earthquake on 16 October 1999.

The M5.1 occurred at the edge of a cluster of off-fault aftershocks of the Hector Mine earthquake. Although the aftershock sequence has largely died down, activity in the area remains higher than the previous low background rate, indicating that the aftershock sequence is continuing. The recent M5.1 is thus considered to be an aftershock of the Hector Mine earthquake.

Earthquake Information for California