Permalink : http://hdl.handle.net/2115/55263

JaLCDOI : 10.14943/gbhu.77.5

An earthquake swarm begun at the end of January, 2012 and the activity reached a peak in middle February, then gradually decreased by the end of April, in the Nigorikawa caldera, Hokkaido. The largest earthquake was the MJMA3.6 event which occurred on 15 February 2012 with maximum intensity 3．Temporal seismic observation with two stations carried out from 20 February to 9 April in the caldera. Detailed hypocenter distribution estimated by using both data temporal and secular observations shows two clusters, one of them is aligned along the northern caldera wall and another is located at eastern outside of caldera. Strike of alignment epicenter of the north cluster shows NE-SW direction, which is in good agreement with one of the nodal plane of focal mechanism of the largest event.