Study of source mechanism of volcanic earthquake and volcanic tremor revealed by broadband seismic observations

在浅间火山，最近在山顶火山口附近安装了另外四个地震站，以便在距离火山口下方的震源区域更近的地方获得高质量的记录。使用新的数据，火山地震的震源被更准确地确定，特别是在深度上。高频地震和低频事件集中在火山口下方1公里以上的浅层区域。在3km以下也观察到一些高频事件，并且在两个带之间存在地震空区。地震空区与由地面形变估计的压力源位置一致。据推断，差距区对应于一个岩浆库和较浅的地震事件发生在和周围的管道到山顶火山口。通过GPS观测，震群与地壳形变有关，形变压力源与火山口下方火山地震同区。震群被认为是由管道压力变化引起的。

ln Asama volcano, additional four seismic stations were recently installed near the summit crater in order to obtain the high quality records in closer distances to the hypocenter regions just below the crater. Using the new data, the hypocenters of the volcanic earthquakes were determined much more accurately, particularly in depth. High frequency earthquakes and low frequency events are concentrated into a shallow zone above the depths of 1 km underneath the crater. Some high frequency events are also observed below 3 km and there is a seismic gap between the two zones. The seismic gap agrees with the location of the pressure source which is estimated from the ground deformation. It is inferred that the gap zone corresponds to a magma reservoir and that shallower seismic events occur in and around the conduit to the summit crater. By GPS observation, the seismic swarm was associated with the crustal deformation and the pressure source of the deformation is the same region as the volcanic earthquakes just bellow the summit crater. The seismic swarm is considered to be caused by the pressure changes of the conduit.