Seismo-Watch

Special Earthquake Report No: 99-006

Preliminary data indicates a significant earthquake has occurred:caption

Regional Location:

Preliminary Magnitude:

Moment Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Latitude:
Longitude:
Focal Depth (km):
Analysis Quality (A-D):

CALIFORNIA-MEXICAN BORDER REGION

4.4 ML (SCSN)

4.1 Mw (Caltech)

99/01/13
13:20:55 (5:21 a.m. PST)
32.69N
115.92W
13.4 km
A

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An earthquake registering a preliminary magnitude of ML 4.4 (Caltech) Mw 4.1 (Caltech)occurred at 13:20:55 UTC (5:21 a.m. PST), January 13, along the Southern California border with Mexico. The focal depth was placed at 13.4 km beneath the surface and the Caltech moment tensor solution suggested strike-slip motion along a northwest or northeast trending fault plane with a slight dip-slip component. The quake was centered about 5 miles southeast of Ocotillo in the Yuha Desert.
 
Preliminary reports indicate the temblor was widely felt in eastern San Diego and western Imperial Counties, but there has been no news of any items toppling off tables or shelves. Several people were jarred from sleep and some reported the quake sounding like a freight train roaring through their home.
 
It occurred at the complex junction of the northern Elsinore fault zone and the southern Laguna Salada fault system, just a few miles north of the Mexican border. The focal mechanism does not sort out whether if the quake occurred along the northwest trending Elsinore-Laguna fault zones or along one of the cross faults in the region (ie; Yuha Wells fault). The quake was part of a brief sequence which included six foreshocks, the largest of which registered M3.8, and followed by two aftershocks, one of which measured as large as M3.2.
 
It was the first M4+ earthquake the region in ten weeks. The last earthquake in the M4+ range to strike the Southern California region was a M4.0 temblor south of Ocotillo in southern Sierra Juarez Valley on November 2.
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Subtract 8 hours from Greenwich Mean Time to obtain PST or 5 hours for EDT
Location Quality: A (good), B (fair), C (poor), D (bad)
Magnitude: Ml (local or Richter magnitude), Lg (mblg), Md (duration), Mb (body wave), Ms (surface wave), Mw (moment)

Standard Sources Include:
U.S. Geological Survey, National Earthquake Information Center, Golden, CO (NEIC)
Harvard Geophysical Observatory, Harvard University, Cambridge, MA (HRV)
U.S. Geological Survey, Northern California Seismic Network (NCSN)
University of California, Berkeley, Seismological Laboratory (UCBSL)
California Institute of Technology, Pasadena, California (Caltech)
various wire reports and/or personal communications

All data are preliminary and subject to change.
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