In October 1995, a mud volcano formed in Mt. Garan, one of cones at Tsurumi Volcano. This produced characteristic seismic events named “Heart beats” with a constant time interval of 1.3 s. Seismic observations were performed around the mud volcano to investigate the source mechanism of the “Heart beats” in April 1996. Assuming homogeneous half-space of Vp=300 m/s based on seismic velocity survey around the mud crater. The source of the “Heart beats” was located at the eastern bottom of the mud volcano. This area was the most fumarolic active region in the crater. The source mechanism of “Heart beats” was determined by evaluating the moment tensor of the initial motion by waveform inversion. Two seismic sources were assumed in order to explain the initial motions and the following large dilatational phases of the “Heart beats.” The “Heart beats” were initiated by normal faulting, and this was followed by volumetric contraction of 0.5×l0-4 m3.
