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Weekly Earthquake Reports
Earthquake Alert Bulletin No: 97-188

Preliminary data indicates a significant earthquake has occurred:

Regional Location:

Preliminary Magnitude:

Moment Magnitude (Mw):

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


4.1 Ml

3.9 Mw (UCB)

19:46:37 (12:46 p.m. PDT)
7.4 km
A moderate earthquake occurred registering a preliminary magnitude of Ml 4.1 occurred at 12:46 p.m. local time, July 17, south of the San Francisco Bay Area near Gilroy. The quake was centered about 3 miles south-southeast of Gilroy and along the Sargent fault. The Moment magnitude solution was determined by the University of California, Berkeley, indicated a strike-slip motion along a NW trending plane - coincident with the orientation of the sargent fault. The quake was sharply felt in the epicentral regional and as far away as San Francisco. There have been no reports of damage or injuries at this time. There have been a couple small aftershocks.
Subtract 7 hours to obtain PDT or 4 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)

Sources Include:
U.S. Geological Survey, National Earthquake Information Center, Golden, CO (NEIC)
Harvard Geophysical Observatory, Harvard University, Cambridge, MA (HRV)
International Data Center, Center for Monitoring Research, Arlington, VA (IDC)
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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