Recent progress on a magnetometer array on the San Andreas Fault



Four highly sensitive optically pumped rubidium vapor magnetometers are in continuous operation along the San Andreas fault near Hollister, California, to detect any local changes in the geomagnetic field, which are associated with earthquakes or creep displacement on the fault. The magnetometer signals are telemetered to a central reference station, and differences are formed in real time to reduce the effect of unwanted micropulsations. A telemetering creep recorder complements the magnetometer array. Local geomagnetic events have indeed been observed, occurring some tens of hours before the onset of local creep displacement. Two types of magnetic signatures are observed.