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Weekly Earthquake Reports
Earthquake Alert Bulletin No: 97-175

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):


2.9 MD


7.5 km
A strong earthquake swarm began at Mammoth Lakes at about 8:00 a.m July 7 and has produced over 175 quake in the following 27 hours. All of the activity has been less than M3 with the strongest quake in the sequence listed above. The activity is centered about 3-5 miles east of the town of Mammoth Lakes near Casa Diablo Hot Springs. This is the southwestern margin of the resurgent dome - a portion of the Long Valley caldera floor which is bowing upwards with the influx of magma. Earthquake swarms have been relatively common the Mammoth lakes since the 1980s with the last major surge in the winter of 1996. As with swarms of this intensity, a Status Alert change to level D has been advised by the USGS.
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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