Vertical distortion in Long Valley, California, associated with the January 1983 earthquake swarm

Beginning in the summer of 1982, a series of repeated, high-precision, gravity measurements have been undertaken in Long Valley, California. Benchmarks have been established from south of Crowley Lake outside the caldera, to Mono Craters in the north. Stations are reobserved at frequent intervals with three Model G, LaCoste-Romberg gravity meters. We observed significant changes in surface gravity associated with the January 1983 earthquake swarm in the south moat of Long Valley caldera. These changes indicate that the ground around the Casa Diablo hot springs area was uplifted at the time of the swarm. The uplift pattern agrees with that predicted by the model of Rundle and Whitcomb, that is, injection of magma into two chambers at 5 to 8 km depth beneath Long Valley Caldera.