Magnitude 5.5 near Portola, CA

Information from UCB, USGS Menlo Park, & UNR
Location:	14 km (9 miles) W of Portola, CA 39.828, -120.632
Date & Time (Local):	2001/08/10 13:19:26.97 (PDT)
Date & Time (UTC):	2001/08/10 20:19:26.97 (UTC)
Depth (km):	14
ML:	5.5
Mw:	5.2
Fault Zone:	Mohawk Valley

This area of California averages a M5 or larger earthquake approximately every 20 years or so. According to Tousson Toppozada of the California Division of Mines and Geology, historical events in this area include:

1875 M 6.2, ~40 km to the NNE near Janesville
1888 M 6.2, ~20 km to the SSW near Blairsden
1959 M 5.6, ~40 km to the ESE near Verdi
1966 M 6.0, ~60 km to the SSE near Truckee

• Details
  • Press Release
  • UCB Moment Tensor solution
  • UCB/USGS Aftershock Warning
    As of 17:00 PM (local time) on 08/12, a number of aftershocks have been recorded. The largest thus far, with M4.2, occurred at 05:01 AM on 08/11.

  • List of events within 50 km from the UC Berkeley catalog

  • More information from the USGS
  • More information from UNR

• Maps
  • RecentEQs quad for this event
  • Map showing M5.5 location
  • Map showing 30 years of M4.0 and larger events
  • Map of large historical earthquakes and recent seismicity in the vicinity of this event - from UNR (also available as PDF file)
  • More maps coming soon!

  • Probabilistic Seismic Hazard Map of this area - from CDMG

• Seismograms
  • Seismogram from ORV BHZ via "Make Your Own Seismogram"
    The BSL station ORV is located ~80 km away from the epicenter of this earthquake. An aftershock at 1:36 PM local time (20:36 UTC) is visible as a low amplitude wiggle on this plot. You can see what is happening at ORV now by checking the current seismograms entry.
  • 3-component recording from ORV
    This figure shows the 3 components of ground motion recorded at ORV, and indicates the arrival times of the P and S waves.
  • BDSN recordings
    This figure shows the recordings from several BDSN stations.
  • "Helicorder Cam"
    From UNR, showing the seismic signal coming in from their station at Battle Mountain, Nevada. (Check the archives if the event is no longer visible.)

• Ground shaking information
  • Northern California Shake Map - see the observed ground motions!
  • Community Internet Intensity Maps - see what other people felt and report your observations!

• Other
  • Photos of landforms near Portola - from the City of Portola