Seismic monitoring at Coso volcanic field
As magma moves through the earth, it displaces and fractures rock along the way. This movement causes earthquakes that can be recorded with seismometers at the surface of the earth. As of 2008, seismic monitoring is the most used technique for volcano surveillance.
Volcanic earthquakes often provide the initial sign of volcanic unrest. Their signals differ from typical, tectonic, earthquakes because they tend to be found at depths shallower than 10 km, are small in magnitude (< 3), occur in swarms, and are restricted to the area beneath a volcano. Harmonic tremor, or volcanic tremor, is the name for the continuous, rhythmic seismic energy associated with underground magma movement.
There is currently one USGS operated seismometer near Coso volcanic field, which was installed in 2001. Monitoring conducted by the U.S. Navy suggests there are common small to moderate earthquakes associated with the geothermal resource.