A M4.2 earthquake occurred in West Hollywood California at 4:59 pm (local time) September 9, 2001. This earthquake was widely felt throughout the Los Angeles Basin and in parts of San Fernando Valley and was well recorded by the Caltech-USGS TriNet. The focal depth of this earthquake was about 4 km, making the shaking most severe in the Hollywood basin. No significant damage has been reported.

During the last two weeks a north-northwest trending cluster of seismicity preceded the M4.2 earthquake. This cluster crossed the epicentral area of the M4.2 extended from Inglewood in the south, to Northridge in the north. These quakes had magnitudes in the range from M1.3 to M2.0.

This earthquake is located near the intersection of the Newport-Inglewood and Hollywood faults. The focal mechanism showed horizontal strike-slip motion on a north-northwest striking plane, suggesting that this event may be associated with the north end of the Newport-Inglewood fault.

The Los Angles basin has north-northwest trending strike-slip faults at shallow depth and east-west trending thrust faults at depths greater than 6 to 8 miles. This earthquake differs from of the deep thrust faulting earthquake sequences recorded over the last two decades in the Los Angeles area such as 1987 M5.9 Whittier Narrows and 1994 M6.7 Northridge. The occurrence of this earthquake cluster suggest activation of the more shallow strike-slip regime of fault s in the Los Angeles basin, which has mostly remained dormant over the last decade.

The M4.2 has so far been followed by the following aftershocks:

MAG    DATE    LOCAL-TIME  LAT     LON    DEPTH    LOCATION
                                   y/m/d     h:m:s     deg     deg     km

2.8  2001/09/09 17:01:01 34.078N 118.396W  3.1  1 km (1 mi) SSE of WestHollywood, CA
2.0  2001/09/09 17:06:22 34.084N 118.390W  6.3  1 km (1 mi) E of West Hollywood,CA
1.8  2001/09/09 17:25:27 34.047N 118.391W 11.5  3 km (2 mi) ESE of Century City,CA