草津白根山における新たな地震観測システムの構築

概要

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Flow properties of volcanic fluids beneath the Kusatsu-Shirane volcano have been studied at the Volcano Fluid Research Center, Tokyo Institute of Technology, by using geochemical methods. A novel seismic observation system, in which seismic signals from two borehole stations newly constructed at the summit are continuously acquired with the data from our previous observation system, started to monitor the activity of the Kusatsu-Shirane volcano in November 2001. The seismic signals are digitized with a 20 or 22bit A/D resolution and a sampling time of 0.01s, and are integrated with the seismic data from the Earthquake Research Institute, University of Tokyo. As a result, the detection capability of earthquakes and the accuracy of hypocenter determination are significantly improved especially in the Yugama region. Volcanic earthquakes in excess of 100 occurrences per month -5 to 10 times the number of earthquakes observed by the Japan Meteorological Agency - were observed by the new system. The observed volcanic earthquakes are tectonic type, with distinct P- and S-waves. A total of 602 earthquake hypocenters were determined between November 2001 and March 2003. The regions of Yugama and north Motoshirane are seismogenic regions in the vicinity of the Kusatsu-Shirane volcano. Seismic activity in north Motoshirane, which was unknown in the past, is equivalent to the activity in Yugama.
特定非営利活動法人日本火山学会の論文
2006-02-28