2018年11月下旬以降の焼岳火山近傍の地震活動について

Abstract

An intense swarm activity took place in the vicinity of the Yake-dake volcano, Hida mountain range, central Japan, in the end of November 2018 and lasted for about three months. The main hypocentral region in November 2018 (Group A) is located at the western flank of Yake-dake volcano, followed by other small activities in the Kamikochi area in December 2018 (Group B), west to the Group A in January 2019 (Group C), and between Yake-dake and Akandana volcanoes beneath the ridge in February 2019 (Group D). Focal mechanism obtained using P-wave first motion indicates NW-SE compressional stress field in Group A. However, there are several events that exhibit normal fault type solution in Group B, which are not consistent with the regional stress field. Temporal change of the geodetic, geomagnetic, geothermal, and geochemical data collected from monitoring stations in the vicinity do not show the clear signals associated with the swarm activity.