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Weekly Earthquake Reports
Earthquake Alert Bulletin No: 97-182

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):


3.0 MD


5.6 km
After a brief pause, significant microseismicity resumed last night at the Long Valley caldera near Mammoth Lakes, California. Following the 31 events/hr surge between 4-5 a.m., Wednesday, July 9, activity sputtered at 0-4 events/hr throughout most of Wednesday and Thursday. A couple of 6-8 event/hr pulses were recorded but nothing substantial. However, after the first M3 event of the 5-day-long, 400+ event earthquake swarm a few seconds before midnight last night (listed above), activity has consistently remained at the 8-16 events/hr level. The 1-2 a.m. hour was the most active with 16 events/hr. The focal depth for the M3.0 quake was 5.6 km and consistent with that of the swarm sequence which has been typically at the 5-8 km depth.
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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