Seismo-Watch Significant Earthquake Report - No. 01-028
Regional Location:

Preliminary Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
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PORTOLA, NORTHEASTERN CALIFORNIA

ML 5.5 (NCSN), ML 5.5 (UNRSL), Mw 5.2 UCBSL

01/08/10
20:19:26 (1:19 p.m. local time)
39.828N
120.632W
14.5 km

PORTOLA M5.5 EARTHQUAKE REPORT (Continued, Page 3)

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Brief Background
The quake occurred along the Mohawk Valley seismic zone, a series of tremors which generally follow the Mohawk Valley fault zone - a prominent series of fault between Sierra Valley and Quincy. Most of the recent tectonic action, however, has occurred slightly to the north of the fault and west of Davis Lake.

Light to moderate tremors have been felt in the area in the last five years, including a M4.2 and a M4.0 in 1998, and a M4.8 in 1997. An expanded search of M4+ activity from Quincy to the Nevada border, and from Sierra Valley to Honey Lake shows that 11 tremors have registered M5.0 or stronger in this aream including four inthe M6 range.

This was the largest earthquake along the California-Nevada border north of Mammoth Lakes since Markleeville (Double Springs Flats) M5.9 earthquake on September 12, 1995. On October 30, 1998, the U.S. Geological Survey measured a M5.3 near Incline but the University of Nevada, Reno, Seismological Laboratory measured it at M4.9 and they probably had a better fix on the data.

Additional Seismic information links:

Seismograms of the earthquake series from nearby stations:
Mainstream media news reports:
Report update: 11:50 p.m., August 11, 2001
Wednesday, August 22, 2001
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