2012 Volume 64 Issue 3 Pages 135-142
We investigated the spatial distribution, temporal change and some statistical features of the swarm activity in Hakone volcano after the 2011 Off the Pacific Coast of Tohoku earthquake (hereafter, the 2011 Tohoku earthquake). Though overall spatial distribution of the activity was not much different from that observed at swarm activities in recent years, its temporal change was quite different: Contrary to recent activities in which burst-like earthquake occurrence was observed repeatedly, the activity after the 2011 Tohoku earthquake declined rather rapidly and monotonously according to an inverse power law of the elapsed time from the 2011 Tohoku earthquake. This feature was most clearly seen in the change of daily number of earthquake clusters. Another notable feature of the activity was that the b value was significantly smaller than the values of recent swarm activities. These characteristics suggest that the swarm activity was induced by the sudden increase of static stress caused by the 2011 Tohoku earthquake on March 11.