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Local Magnetic Field Variations and Stress Changes Near a Slip Discontinuity on the San Andreas Fault

  • M. J. S. Johnston
Conference paper
  • 38 Downloads
Part of the Advances in Earth and Planetary Sciences book series (AEPS, volume 5)

Abstract

Data from an array of proton magnetometers in central California indicate that a systematic decrease in magnetic field of about 2 γ in 5 years has occurred in a localized region near Anzar, California, just north of the creeping section of the San Andreas fault. This field change has most likely resulted from changes in crustal stress in this region, although an unknown second-order effect of secular variation cannot be excluded as a alternate explanation. Tectonomagnetic models have been developed using dislocation modeling of slip on a finite section of fault. Assuming a fault geometry and rock magnetization, these models relate changes in stress, fault slip, and fault geometry to surface magnetic field anomalies. A large-scale anomaly, opposite in sense to that observed but of similar amplitude, would be expected to have accumulated in this area during the past 70 years. A localized 5-bar decrease in shear strain on the fault resulting from about 2 cm of slip on a 0.25-km square patch at a depth of 1 km beneath the surface trace of the fault opposite the magnetometer could explain the observed data and still be compatible with the geodetic strain measurements in the area. Other models of limited local slip are equally possible. The occurrence of a moderate magnitude earthquake in this region will allow comparison of stress changes estimated by different techniques.

Keywords

Magnetic Anomaly Stress Change Secular Variation Fault Slip Fault Geometry 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Atwater, T. and P. Molnar, Relative motion on the Pacific and North American plates deduced from sea floor spreading in the Atlantic, Indian and South Pacific oceans, in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, edited by R.L. Kovach and A. Nur, pp. 136–148, School of Earth Sciences, Stanford University, Stanford, California, 1973.Google Scholar
  2. Bolt, B.A. and R.D. Miller, Catalogue of earthquakes in northern California and adjoining Areas— January 1910–13 December 1972, Bulletin of the Seismographic Stations, University of California, Berkeley, 568 pp., 1975.Google Scholar
  3. Brune, J.N., Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res., 75, 4997–5009, 1970.CrossRefGoogle Scholar
  4. Brune, J.N., T.L. Henyey, and R.F. Roy, Heat for, stress, and rate of slip along the San Andreas fault, California, J. Geophys. Res., 74, 3821–3828, 1969.CrossRefGoogle Scholar
  5. Chinnery, M.A., The stress changes that accompany strike-slip faulting, Bull. Seismol. Soc. Am., 53, 921–932, 1963.Google Scholar
  6. Chinnery, M.A. and J.A. Petrak, The dislocation model with variable discontinuity, Tectonophysics, 5, 513–529, 1968.CrossRefGoogle Scholar
  7. Friedman, M.E., J.H. Whitcomb, C.R. Allen, and J.A. Hileman, Seismicity of the Southern California Region, 1 January 1972 to 31 December 1974, Seismological Laboratory, California Institute of Technology, Pasadena, California, 81 pp., 1976.Google Scholar
  8. Hanna, W.F., R.D. Brown, D.C. Ross, and A. Griscom, Aeromagnetic reconnaissance along the San Andreas fault between San Francisco and San Bernardino, California: U.S. Geological Survey, Geophys. Inv. Map GP 815, scale 1:250,000, 1972.Google Scholar
  9. Hilderbrand, T., Seismomagnetism, Ph.D. thesis, University of California, Berkeley, 1975.Google Scholar
  10. Hileman, J.A., C.R. Allen, and J.M. Nordquist, Seismicity of the southern California region 1 January 1932 to 31 December 1972, Seismological Laboratory, California Institute of Technology, Pasadena, 404 pp., 1973.Google Scholar
  11. Johnston, M.J.S., B.E. Smith, and R. Mueller, Tectonic experiments and observations in western U.S.A., J. Geomag. Geoelectr., 28, 85–97, 1976.CrossRefGoogle Scholar
  12. Lachenbruch, A.H. and J.H. Sass, Thermo-mechanical aspects of the 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. 192–205, School of Earth Sciences, Stanford University, Stanford, California, 1973.Google Scholar
  13. McHugh, S. and M.J.S. Johnston, Dislocation modelling of creep related tilt changes, Bull. Seismol. Soc. Am., 68, 155–168, 1978.Google Scholar
  14. Ohnaka, M. and H. Kinoshita, Effect of uniaxial compression on Remanent Magnetization, J. Geomag. Geoelectr., 20, 93, 1968a.CrossRefGoogle Scholar
  15. Ohnaka, M. and H. Kinoshita, Effect of axial stress upon initial susceptibility of an assemblage of fine grains of Fe2TiO4-Fe3O4solid solution series, J. Geomag. Geoelectr., 20, 107, 1968b.CrossRefGoogle Scholar
  16. Prescott, W. and J.C. Savage, Strain accumulation rates in the western United States between 1970 and 1976, J. Geophys. Res., 1978 (in press).Google Scholar
  17. Press, F., Displacements, strains and tilts at teleseismic distances, J. Geophys. Res., 70, 2395–2412, 1965.CrossRefGoogle Scholar
  18. Rosenman, M. and S.J. Singh, Quasi-static strains and tilts due to faulting in a viscoelastic halfspace, Bull. Seismol. Soc. Am., 63, 1737–1742, 1973.Google Scholar
  19. Shamsi, S. and F.D. Stacey, Dislocation models and seismomagnetic calculations for California 1906 and Alaska 1964 earthquakes, Bull. Seismol. Soc. Am., 59, 1435–1448, 1969.Google Scholar
  20. Sieh, K., Pre-historic large earthquakes on the San Andreas fault in the area of the Palmdale Uplift, EOS, Trans. Am. Geophys. Union, 57, 899, 1976.Google Scholar
  21. 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
  22. Spottiswood, S.M. and A. McGarr, Source parameter of tremors in a deep-level gold mine, Bull. Seismol. Soc. Am., 65, 93–112, 1975.Google Scholar
  23. Stacey, F.D., The seismomagnetic effect, Pure Appl. Geophys., 58, 5–22, 1964.CrossRefGoogle Scholar
  24. Stacey, F.D. and M.J.S. Johnston, Theory of the piezomagnetic effect in titanomagnetite bearing rocks, Pure Appl. Geophys., 97, 146–155, 1972.CrossRefGoogle Scholar
  25. Stesky, R.M. and W.F. Brace, Estimation of frictional stress on the San Andreas fault from laboratory measurements, in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, edited by R.L. Kovach and A. Nur, pp. 206–213, Stanford University Publications, 1973.Google Scholar
  26. Talwani, P. and R.L. Kovach, Geomagnetic observations and fault creep in California, Tectonophysics, 14, 245–256, 1972.CrossRefGoogle Scholar
  27. Toppazada, T.R., D.L. Parke, and C.T. Higgins, Seismicity of California, 1900–1931, unpublished manuscript, 1976.Google Scholar
  28. 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
  29. Williams, F.J. and M.J.S. Johnston, Differential magnetometer measurements on the Palmdale Bulge, and along the San Jacinto fault, EOS, Trans. Am. Geophys. Union, 57, 898, 1976.Google Scholar

Copyright information

© Center for Academic Publications Japan 1979

Authors and Affiliations

  • M. J. S. Johnston
    • 1
  1. 1.U.S. Geological SurveyMenlo ParkUSA

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