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

Research Project

Project/Area Number	12640403
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	固体地球物理学
Research Institution	The University of Tokyo
Principal Investigator	IDA Yoshiaki Earthquake Research Institute, Professor, 地震研究所, 教授 (30013535)
Co-Investigator(Kenkyū-buntansha)	OIKAWA Jun Earthquake Research Institute, Research Associate, 地震研究所, 助手 (40262084)
Project Period (FY)	2000 – 2001
Project Status	Completed (Fiscal Year 2001)
Budget Amount *help	¥3,600,000 (Direct Cost: ¥3,600,000) Fiscal Year 2001: ¥500,000 (Direct Cost: ¥500,000) Fiscal Year 2000: ¥3,100,000 (Direct Cost: ¥3,100,000)
Keywords	Volcanic earthquake / Volcanic tremor / Asama volcano / Magma reservoir / Free oscillations of a fluid sphere / Eruption / Pressure source under a summit crater / 広帯域地震観測 / A型地震 / B型地震 / N型地震 / 火山性流体 / 発生機構 / 浅間山 / 火山性地震・微動 / マグマ / 火山ガス
Research Abstract	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.