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M 5.4 (SCSN)

1.2 km (0.7 miles)

Big Bear M 5.4 earthquake shakes a wide area

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Saturday, February 22, 2003

An earthquake registering M 5.4 occurred early this morning about 90 miles east of Los Angeles in the San Bernardino Mountains near Big Bear City, jarring residents awake and shaking buildings over a wide area, but not causing any serious damage or injuries. Five aftershocks in the M 4.0+ range occurred within the first six hours of the main shock, frightening many people and contributing to the minor damage reported.

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According to the Southern California Seismic Network (SCSN), the earthquake measured M 5.4 occurred at 4:19 a.m. PST (or 12:19:10 GMT), February 22, about 90 miles east of Los Angeles, 29 miles northeast of San Bernardino, and 3 miles north of Big Bear City, in the San Bernardino Mountains. It was centered on the north side of Gold Mountain at Union Flats. See a Topozone topographic map or a MapQuest street map.

The focal depth was rather shallow, only 1.2 km (0.7 mi.) beneath the surface. Most of the earthquake activity in the San Bernardino Mountains tends to occur between 5-9 km deep and activity this shallow is uncommon.

A preliminary fault plane solution by UC Berkeley indicated strike-slip motion along a northwest-southeast. Preliminary data shows the aftershocks form a 2 mile long, northwest striking trend that represent the source of the fault. The Helendale fault, a nearby northwest-trending fault two miles to the east, has been the site of several small to moderate earthquakes in the past and a splay or offshoot may have been responsible for today's quake.

Continued on Page 2 >>

Report update: 10:02:41 AM, Monday, February 24, 2003

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