Seismic monitoring at Medicine Lake
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.
The seismic network at Medicine Lake volcano includes five seismometers. The network was installed in 1978 and the most recent instrument was added in 2009. The most notable seismicity over the last three decades was a series of shallow earthquakes in 1988-89 (magnitudes of 4.1 and less).