Seismo-Watch

More Special Earthquake Reports

January 28, 2002

An earthquake measuring M4.2 occurred this evening near the Los Angeles-Ventura County line north of Simi Valley, shaking a wide area but not causing any damage or injuries.

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According to the Southern California Seismic Network (SCSN) the earthquake measured a Local magnitude (ML) of 4.2 and occurred at 05:53 GMT, January 29 or 9:53 p.m. PST, Monday, January 28, about 32 miles northwest of Los Angeles, 8 miles north-northwest of Chatsworth, and 6 miles north-northeast of Simi Valley in the Santa Susana Mountains. See a Topozone topographic map or a MapQuest street map.

The focal depth was at 13.7 km (8.3 miles), a typical depth for earthquakes in this area.

A preliminary analysis by TriNet suggests the earthquake occurred along a moderately dipping, east-west trending plane and the type of fault slip was thrust (up and over). See fault plane solution.

Foreshocks and aftershocks
A foreshock measuring M3.1 triggered about 30 seconds before the main shock.

See a clip of the NBC4 Seis-Cam showing part of the Simi Valley earthquake series.

The quake was followed by about two dozen aftershocks within the first few hours, including two light jots, a M3.9 at about 34 seconds past 10 o'clock and a M3.8 about eight minutes later at 10:08 p.m. Both of these quakes were widely felt in the region and caused additional concern for the local residents.

Smaller aftershocks in the M2 range have been reportedly felt.

More Info on Page 2