Low velocity zone under Long Valley as determined from teleseismic events

This is the published version. Copyright 1976 American Geophysical Union. All Rights Reserved.A temporary seismograph station network was used to estimate teleseismic P wave residuals in the vicinity of Long Valley geothermal area, California. Relative P wave delays of 0.3 s persist at stations in the west central part of the Long Valley caldera after regional and near-surface effects have been removed. Ray tracing indicates that low-velocity material exists beneath the caldera at depths greater than 7 km and less than 40 km, probably less than 25 km. The velocity contrast with normal crust must be at least 5% to satisfy the data and is probably in the range 10–15%. We believe that the low velocity indicates anomalously hot rock at depth and that relative teleseismic P residuals may be useful for investigation of sources of geothermal energy