AVL operates the seismic, geodetic, and geomagnetic observations for research on the Aso, Kuju, and Tsurumi active volcanoes. Volcanic earthquakes beneath the crater can be divided into two kinds, high frequency events and low frequency ones.
Studies show that their source mechanisms are different before and after the eruptions.
The changes in the amplitude and the period of volcanic tremors are remarkably recognized to be closely related to eruptive activities. The very long period tremors are observed by the broadband seismometers. The period is 15 seconds. This long period tremor always occurs every ten minutes. The telemetric seismic network around the caldera and others consists of 22 stations.