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Ultra-low frequency electromagnetic monitoring of the San Andreas Fault

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spectrogram graph
48-hr spectrogram of vertical magnetometer, Jasper Ridge field electromagnetic observatory

The Stanford ultra-low frequency electromagnetic (ULFEM) Monitoring Project is recording naturally varying electromagnetic signals adjacent to active earthquake faults, in an attempt to establish whether there is any variation in these signals before or after earthquakes.



Our project is collaborative with the U.S. Geological Survey and U.C. Berkeley.  Lead scientists are Simon Klemperer (Stanford University), Jonathan Glen (U.S.G.S.) and Darcy Karakelian McPhee (U.S.G.S.)



Our initial sites are in the San Francisco Bay Area, monitoring different strands of the San Andreas fault system, and Jasper Ridge (JRSC), Marin Headlands (MHDL), and Briones (BRIB).  Related sites in the greater San Francisco Bay Area are operated by U.C. Berkeley and by Quakefinder.


Stanford University, in co-operation with the U.S.G.S. and with assistance from U.C. Berkeley, maintains three sites in the San Francisco Bay Area, monitoring different strands of the San Andreas fault system.  These three sites (Jasper Ridge (JRSC), Marin Headlands (MHDL), and Briones (BRIB)) have three orthogonal magnetometers, and JRSC and BRIB additionally have two pairs of orthogonal 100-m horizontal electrodes.  Our equipment is sensitive to natural field variations in the frequency (period) range 0.01 to 10 Hz (100 to 0.1 s).

Data sampled at 40 Hz are available online from three stations maintained by Stanford University in co-operation with the U.S.G.S and with asistance from U.C. Berkeley:

and from two stations maintained by U.C. Berkeley with assistance from the U.S.G.S. and Stanford University:

Station metadata can be found at the Berkeley Digital Seismic Network (BDSN) and Northern California Earthquake Data Center (NCEDC) sites including a brief listing of station location and operation dates and a description of each available channel

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