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

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