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Ultra-low frequency electromagnetic monitoring of the San Andreas Fault

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:

    (JRSC) Jasper Ridge Biological Preserve, Stanford University
    (MHDL) Marin Headlands, Golden Gate National Recreation Area
    (BRIB) Russell Reservation, Briones Reserve, U.C.

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

    (SAO) San Andreas Geophysical Observatory, Hollister
    (PKD) Bear Valley Ranch, Parkfield

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.



2013   Fraser-Smith, A.C., McPhee, D.K., Glen, J.M., Klemperer, S.L., McGill, P.R., and Bernardi, A.  Comments on "On the reported magnetic precursor of the 1989 Loma Prieta earthquake" by J. N. Thomas, J. J. Love, and M. J. S. Johnston, Physics of the Earth and Planetary Interiors. 


2012  Christman, L., Connor, D., McPhee, D.K., Glen, J.M., and  Klemperer, S.L.  Characterizing potential earthquake signals on the Stanford-USGS ultra-low frequency electromagnetic (ULFEM) array.  EOS Trans. AGU Abstract NH41B-1608 presented at 2012 Fall Meeting, AGU, San Francisco, CA. 

2012  Connor, D., Klemperer, S.L., Glen, J.M., and McPhee, D.K., Stanford-USGS Ultra-Low Frequency Electromagnetic Network: Magnetometer Calibration Developments.  Poster presented at 2012 Annual Biomedical Research Conference for Minority Students (ABRCMS), San Jose, CA, 11/28/2012. 


2010 Bowden, D.C.., Engelland-Gay, H., Enright, A., Gardner, J., Klemperer, S.L., McPhee, D.K., Glen, J.M.  Stanford-USGS Ultra-low frequency electromagnetic network: hardware developments in magnetometer calibration and recording. EOS Trans. AGU, Abstract NH31A-1338 presented at 2010 Fall Meeting, AGU, San Francisco, CA.

Download Document(s): PDF icon bowden-Henry-ULFEM-2010AGU-v11

2010 Neumannn, D.A., McPherson, S., Klemperer, S.L., Glen, J.M.G, McPhee, D.K, and Kappler, K., Documentation for a web site to serve ULF-EM (Ultra-Low Frequency Electromagnetic) data to the public: U.S. Geological Survey Open-File Report 2010-1321, 44 p.


2009   Garber, J.H., Klemperer, S.L., McPhee, D.K., Glen, J.M., 2009. Temporal Changes in Apparent Resistivity on the Stanford-USGS Ultra-Low Frequency Electromagnetic Network. EOS Trans. AGU, 89 (52), Fall Meet. Suppl., Abstract NH31C-1129.


2008   Neumann, D.A., McPherson, S.-L., Kappler, K., Klemperer, S., Glen, J., and McPhee, D. Stanford–USGS Ultra-Low Frequency Electromagnetic Network: Status report and and data availability via the Web. EOS Trans. AGU, 88 (52), Fall Meet. Suppl., Abstract S53B-1824.


2007   Culp, D., Klemperer, S., Glen, J., and McPhee, D. Re-affirming the Magnetic Precursor to the 1989 Loma Prieta, CA, Earthquake Using Magnetic Field Data Collected in the US in 1989 and 1990. EOS Trans. AGU, 87 (52), Fall Meet. Suppl., Talk Abstract S41D-03. 


2005   Bijoor, S., Glen, J., McPhee, D.K., and Klemperer, S.L., Ultra-low Frequency Electromagnetic Monitoring of Earthquakes in the San Francisco Bay Area: Initial Results of an Earthscope PBO Project, EOS Trans. AGU, 86 (52), Fall Meet. Suppl., Abstract T51B-1343.