HR: 0800h
AN: V21C-0619    [Abstracts]
TI: Volcanic conduit system beneath Aso volcano, Japan inferred from broadband seismic observation and numerical simulation of a fluid-filled crack
AU: * Yamamoto, M
EM: mare@zisin.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Aramaki-Aza Aoba 6-3, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Kawakatsu, H
EM: hitosi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kaneshima, S
EM: kane@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551 Japan
AU: Ohkura, T
EM: bonkura@aso.vgs.kyoto-u.ac.jp
AF: Aso Volcanological Laboratory, Institute for Geothermal Sciences, Kyoto University, Minami-Aso, Aso, Kumamoto, 869-1404 Japan
AB: Volcanic tremors are considered to be generated by the motion of volcanic fluid like magma and volcanic gases, and the elucidation of these signals is one of the critical keys to understand the dynamics of the volcanic system. In this study, as a tool to interpret the source process of volcanic tremors quantitatively, we develop a method to numerically simulate the dynamics of a fluid-filled crack, which is considered to be one of the most plausible models of the source of volcanic tremors. We formulate the motion of fluid and elastic solid inside and outside the crack using boundary integrals, and develop a numerical scheme most suitable to solve dynamic interactions between fluid and elastic solid. The newly developed method is more efficient compared to the conventional modeling method using the time-domain finite difference method, and enables us to study the dynamics of the fluid-filled crack over the wide range of physical parameters. We further apply the method to the analyses of volcanic tremors observed at Aso volcano, Japan. Our field observations so far reveal that long-period tremors (LPTs) with a period of 15 sec are generated by a resonance of a crack-like conduit beneath the active crater of the volcano, and short-period tremors (SPTs) with a period of 0.5-1.0 sec, which occur simultaneously with LPTs, are caused by a radial motion of cylindrical source at the top part of the crack-like conduit. To obtain more detailed image of the volcanic conduit system generating LPTs and SPTs, in this study, we conduct extensive numerical simulations of the motion of crack-like conduit using the newly developed method, and estimate the parameters of crack-like conduit such as the geometry of the crack and the properties of the fluid inside the crack from the observed characteristics of LPTs. Using the estimated parameters, we also simulate the behavior of the conduit system, and reveal that SPTs is caused by the fluid motion associated with the resonance of the crack (LPTs). These results suggest that the tremors with different frequencies, which have been separately studied, are driven by a single volcanic conduit system.
DE: 7280 Volcano seismology (8419)
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005