Seismo-Watch Significant Earthquake Report - No. 01-029
Regional Location:

Preliminary Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Focal Depth:


Ml 4.4 (SCSN)

18:04:32 (11:04 a.m. local time)
0.0 km (near surface)


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Felt Reports
The temblor was widely felt in the region and mostly along the coast of Southern California, but did not cause a damage.

The USGS's Community Internet Intensity Maps indicated the main M4.4 jolt was felt from Ventura County to San Diego County but mostly along the coastal communities. An exception came from a few, isloated reportd from some Inland Empire towns, such as Riverside, Redlands and San Bernardino.

Most people described the shaking as a light rolling sensation, lasting approximately 5-10 seconds.

Did you feel this quake? Tell us what you felt. We want to know.

There were no reports of items toppling from tables and shelves and only a few residence in tall buildings indicated slightly stronger shaking than the others.

Brief Background
The quake occurred along the San Clemente fault zone, a series of northwest trending faults and fault segments that includes the San Isidro fault zone south of the Mexican border. The northern extension is not well understood and appears to merge with the Santa Catalina fault zone.

The total length of the entire San Clemente-San Isidro fault zone is on the order of 210 km (130 miles) which suggests it is capable of significant earthquakes in the M7+ range.

This was the first M4+ temblor in Southern California south of the Transverse Range since the Big Bear M5.1 earthquake on February 10 - more than six months ago, a seismic gap of unusual length.

Past activity along the San Clemente fault zone has been sporadic yet has produced M4+ action about 1-3 times each decade. However, this activity has been increasing of late, as four M4s occurred in the 1990s and three M4s have been recorded during the first two years of this decade. See lists of M3+ quakes and M4+ quakes.

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Report update: 9:00 p.m., August 16, 2001

Wednesday, August 22, 2001
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