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CENTRAL CALIFORNIA COAST

ML 4.7 (NCSN) Mw 4.6 (UCBSL)

01/12/28
21:14:01
36.64N
121.25W
6.8 km (4.2 miles)

Moderate 4.7 earthquake hits Central California Coast

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December 28, 2001

Preliminary data indicates that an earthquake measuring M4.7 occurred in the Central California Coast Range at 1:14 p.m. this afternoon, shaking a wide area but not causing any damage or injuries.

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According to the Northern California Seismic Network (NCSN) the earthquake measured a Local magnitude (ML) of 4.7 and occurred at 21:14 GMT or 1:14 p.m. PST, December 28, about 17 miles south-southeast of Hollister and 10 miles northwest of the Pinnacles along the eastern flank of the Gablian Range, near the junction of Old Airport Road and Highway 25 at bear Canyon. See a Topozone topographic map or a MapQuest street map.

The focal depth was at 6.8 km (4.2 miles), a typical depth for earthquakes here.

The UC Berkeley Seismological Laboratory (UCBSL) report a Moment magnitude (Mw) of 4.6, slightly less than the Local magnitude reading. Their Moment Tensor solution indicated strike-slip motion along a northwest trending plane. (See moment tensor)

The earthquake occurred along the San Juan Bautista segment of the San Andreas Fault. This portion of the nearly state-long fault experiences abundant microseismicity and is referred to as the "creeping segment".

Felt Reports
Early reports indicate the earthquake was felt over a wide area of Central California from the San Jose to Monterey. No reports have been received that items toppled from tables or shelves.

There have been no reports of ant serious damage or injuries at this time, and none would be expected from an earthquake of this magnitude in this location.

Aftershocks
It has been followed by a half dozen aftershocks within the first hour, a few of which registered in the M2 range but nothing larger.

There was an early report of an earthquake registering M4.1 near Cholame but this later determined not to be an earthquake and data was removed from the catalog.

Background Information
This is the largest earthquake along this segment of the San Andreas Fault since a M5.4 temblor struck near San Juan Bautista on August 12, 1998. It broke a 25-week gap in M4+ activity in Central California. (See weekly map and graph of Central California earthquake activity here)

A M4.1 temblor triggered a few miles to the northwest on July 2 - a little more than six months ago.

Additional seismic information links:

Mainstream media news reports:
  • None at this time.
Report update: 3:20:51 PM, Friday, December 28, 2001
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