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增加了四个地震台站，以便在火山口下方较近的距离内获得高质量的记录。利用这些新数据，火山地震的震源得到了更精确的确定，尤其是深度。高频率地震和低频率地震集中在火山口下方1公里深度以上的浅层区域。在3公里以下也观察到一些高频事件，两个带之间存在地震间隙。地震间隙与地面变形估计的压力源位置吻合。推断该断裂带与岩浆储层相对应，在通往山顶火山口的管道内及其周围发生浅层地震事件。通过GPS观测，地震群与地壳变形有关，变形的压力源与火山地震位于山顶火山口下方的同一区域。地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.