Seismo-Watch

Special Earthquake Report No: 99-006

Regional Location:

Preliminary Magnitude:

Moment Magnitude:

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

Parkfield, Central California

4.0 Ml (NCSN)

4.0 Mw (UCB)

99/02/26
15:25:56
35.95N
120.49W
10.5 km
A

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An earthquake registering a preliminary magnitude of ML 4.0 (NCSN), Mw 4.0 (UCB occurred at 15:25:56 UTC (7:26 a.m. PST), February 26, in Central California. The focal point was placed at 5 km beneath the surface for quick processing and the University of California, Seismological Laboratory, fault plane solution suggested strike-slip motion along a northwest trending fault plane.
 
The quake was centered on the San Andreas fault about 5 miles north-northwest of Parkfield near Middle Mountain (see map).
 
Seismo-Watch has received felt reports from as far away as Paso Robles, about 20 miles to the southwest. The quake was not large enough to cause any items to topple from tables and shelves.
 
The quake occurred within the "Parkfield Experiment", a segment of the San Andreas fault thought to be the initiation spot for a major earthquake in the future. This quake will trigger emergency response personnel into a ready position. We do not have the statistics of foreshock probability at this time and will keep you informed of any developments.
 
Click here for more info about the USGS Parkfield experiement.
 

Here is a list of M4+ earthquakes in the Parkfield area since 1975:
1975/01/06 11:17:12.11  35.9427 -120.5142  10.81  M4.40  
1975/09/13 21:20:58.99  35.9967 -120.5463  11.21  M4.80  
1982/06/25 03:58:23.15  35.9730 -120.5207   8.76  M4.00  
1987/10/01 14:49:48.21  36.1200 -120.7640  14.12  M4.60 
1992/10/20 05:28:08.90  35.9285 -120.4728  10.21  M4.30 
1993/04/04 05:21:25.27  35.9413 -120.4925   7.65  M4.20 
1993/11/14 12:25:34.87  35.9527 -120.4968  11.70  M4.60 
1994/12/20 10:27:47.17  35.9175 -120.4643   9.10  M4.70
1999/02/26 15:25:56.70  35.95   -120.49    10.50  M4.05
Time is GMT.

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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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