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.
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References
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.
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.
Brune, J.N., Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res., 75, 4997–5009, 1970.
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.
Chinnery, M.A., The stress changes that accompany strike-slip faulting, Bull. Seismol. Soc. Am., 53, 921–932, 1963.
Chinnery, M.A. and J.A. Petrak, The dislocation model with variable discontinuity, Tectonophysics, 5, 513–529, 1968.
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.
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.
Hilderbrand, T., Seismomagnetism, Ph.D. thesis, University of California, Berkeley, 1975.
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.
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.
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.
McHugh, S. and M.J.S. Johnston, Dislocation modelling of creep related tilt changes, Bull. Seismol. Soc. Am., 68, 155–168, 1978.
Ohnaka, M. and H. Kinoshita, Effect of uniaxial compression on Remanent Magnetization, J. Geomag. Geoelectr., 20, 93, 1968a.
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.
Prescott, W. and J.C. Savage, Strain accumulation rates in the western United States between 1970 and 1976, J. Geophys. Res., 1978 (in press).
Press, F., Displacements, strains and tilts at teleseismic distances, J. Geophys. Res., 70, 2395–2412, 1965.
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.
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.
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.
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.
Spottiswood, S.M. and A. McGarr, Source parameter of tremors in a deep-level gold mine, Bull. Seismol. Soc. Am., 65, 93–112, 1975.
Stacey, F.D., The seismomagnetic effect, Pure Appl. Geophys., 58, 5–22, 1964.
Stacey, F.D. and M.J.S. Johnston, Theory of the piezomagnetic effect in titanomagnetite bearing rocks, Pure Appl. Geophys., 97, 146–155, 1972.
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.
Talwani, P. and R.L. Kovach, Geomagnetic observations and fault creep in California, Tectonophysics, 14, 245–256, 1972.
Toppazada, T.R., D.L. Parke, and C.T. Higgins, Seismicity of California, 1900–1931, unpublished manuscript, 1976.
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.
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.
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Johnston, M.J.S. (1979). Local Magnetic Field Variations and Stress Changes Near a Slip Discontinuity on the San Andreas Fault. In: Fuller, M., Johnston, M.J.S., Yukutake, T. (eds) Tectonomagnetics and Local Geomagnetic Field Variations. Advances in Earth and Planetary Sciences, vol 5. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-9825-0_6
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DOI: https://doi.org/10.1007/978-94-010-9825-0_6
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