Local Variations in Magnetic Field, Long-Term Changes in Creep Rate, and Local Earthquakes along the San Andreas Fault in Central California

  • B. E. Smith
  • M. J. S. Johnston
  • R. O. Burford
Conference paper
Part of the Advances in Earth and Planetary Sciences book series (AEPS, volume 5)


Comparison between local variations in magnetic field, long-term changes in creep rate, and local earthquakes have been made for the seismically active and creeping section of the San Andreas fault between the most southern extent of the 1906 earthquake fault break and the most northern extent of the 1857 break, for the period early 1974 through mid-1977. The data utilized are from stations located near the two ends of this section of the San Andreas fault where strain accumulation is expected. The proton precession magnetometer stations included in this study have recorded local magnetic field variations up to 1.8 γ with durations of a few minutes to several months. The creep data indicated changes in creep rate of up to 10 mm/year lasting for 6 months or more and a close similarity between the changes in creep rate on two adjacent creepmeters about 7 km apart. Earthquakes with magnitudes less than 4.0 do not appear to correspond in time to local changes in magnetic field greater than 0.75 γ or variations in the creep rate. There is no general correspondence between creep events and magnetic field variations. There is, however, an approximate correspondence, in both space and time, between the long-term changes in creep rate and the variations in magnetic field. In order to explain the observations presented in this study, it appears necessary to allow for a substantial amount of deep aseismic slip without any obvious attendant changes in the time distribution or size of the local earthquakes.


Creep Rate Local Earthquake Creep Data Creep Event Magnetic Field Change 
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  1. Bakun, W.K., C.G. Bufe, and R.M. Stewart, Body wave spectra of central California earthquakes, Bull. Seismol. Soc. Am., 66, 363–384, 1976.Google Scholar
  2. Burford, R.O., Fluctuations in rates of fault creep associated with moderate earthquakes along the central San Andreas fault, EOS, Trans. Am. Geophys. Union, 57, 1012, 1976.Google Scholar
  3. Johnston, M.J.S., Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault, J. Geomag. Geoelectr., 30, 511–522, 1978.CrossRefGoogle Scholar
  4. Johnston, M.J.S., B.E. Smith, and R.J. Mueller, Tectonic experiments and observations in western U.S.A., J. Geomag. Geoelectr., 28, 85–97, 1976a.CrossRefGoogle Scholar
  5. Johnston, M.J.S., S. McHugh, and R.O. Burford, On simultaneous tilt and creep observations on the San Andreas fault, Nature, 260, 691–693, 1976b.CrossRefGoogle Scholar
  6. Johnston, M.J.S., B.E. Smith, and R.O. Burford, Local magnetic field measurements and fault creep observations on the San Andreas fault, Tectonophysics, 1978 (in press).Google Scholar
  7. McHugh, S. and M. Johnston, Short period nonseismic tilt perturbations and their relation to episodic slip on the San Andreas fault, J. Geophys. Res., 81, 6341–6345, 1976.CrossRefGoogle Scholar
  8. Mortensen, C.E., R.C. Lee, and R.O. Burford, Simultaneous tilt, strain, creep, and water level observations at the Cienega Winery south of Hollister, California, Bull. Seismol. Soc. Am., 67, 641–650, 1977.Google Scholar
  9. Rikitake, T., Earthquake Prediction, pp. 197–211, Elsevier, Amsterdam, 1976.Google Scholar
  10. Savage, J.C. and R.O. Burford, Discussion of paper by C.H. Scholz and T.J. Fitch, Strain accumulation along the San Andreas fault, J. Geophys. Res., 86, 6469–6479, 1971.CrossRefGoogle Scholar
  11. Slater, L.E. and R.O. Burford, A comparison of long-baseline strain data and fault creep records obtained near Hollister, California, Tectonophysics, 1978 (in press).Google Scholar
  12. Smith, B.E. and M.J.S. Johnston, A tectonomagnetic effect observed before a magnitude 5.2 earthquake near Hollister, California, J. Geophys. Res., 81, 3556–3560, 1976.CrossRefGoogle Scholar
  13. Stacey, F.D. and S.K. Banerjee, The Physical Principles of Rock Magnetization, pp. 146–155, Elsevier, Amsterdam, 1974.Google Scholar
  14. Stuart, W.D. and M.J.S. Johnston, Tectonic implications of anomalous tilt before central California earthquakes, EOS, Trans. Am. Geophys. Union, 56, 1196, 1974.Google Scholar
  15. Talwani, P. and R.L. Kovach, Geomagnetic observations and fault creep in California, Tectonophysics, 6, 69–73, 1972.Google Scholar
  16. Thatcher, W. and T.C. Hanks, Source parameters of southern California earthquakes, J. Geophys. Res., 78, 8547–8576, 1973.CrossRefGoogle Scholar
  17. Wesson, R.L., R.O. Burford, and W.L. Ellsworth, Relationship between seismicity, fault creep and crustal loading along the central San Andreas fault, in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, edited by R.L. Kovach and A. Nur, pp. 303–321, School of Earth Sciences, Stanford University, Stanford, California, 1973.Google Scholar
  18. Yamashita, P.A. and R.O. Burford, Catalog of preliminary results from an 18-station creepmeter network along the San Andreas fault system in central California for the time interval June 1969 to June 1973, U.S. Geol. Surv. Open File Report, 215 pp., 1973.Google Scholar

Copyright information

© Center for Academic Publications Japan 1979

Authors and Affiliations

  • B. E. Smith
    • 1
  • M. J. S. Johnston
    • 1
  • R. O. Burford
    • 1
  1. 1.U.S. Geological SurveyMenlo ParkUSA

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