HR: 1340h
AN: G53B-0890    [Abstracts]
TI: Ground deformation of Asama Volcano, Japan, associated with the 2004-2005 unrest
AU: * Aoki, Y
EM: yaoki@eri.u-tokyo.ac.jp
AF: Earthquake Research Insitute, University of Tokyo, 1-1 Yayoi 1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Watanabe, H
EM: watanabe@eri.u-tokyo.ac.jp
AF: Earthquake Research Insitute, University of Tokyo, 1-1 Yayoi 1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Koyama, E
EM: etsu@eri.u-tokyo.ac.jp
AF: Asama Volcano Observatory of Earhquake Research Institute, University of Tokyo, 2125 Nagakura, Karuizawa, Nagano, 389-0011 Japan
AU: Oikawa, J
EM: oikawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Insitute, University of Tokyo, 1-1 Yayoi 1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Morita, Y
EM: morita@eri.u-tokyo.ac.jp
AF: Earthquake Research Insitute, University of Tokyo, 1-1 Yayoi 1, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Ground deformation of Asama Volcano, Japan, associated with the most recent eruptions started on September 1, 2004, is reported. The ground deformation observed by continuous Global Positioning System measurements was modeled by dike intrusion for two different periods; one is between July, 2004, to March, 2005, which represents overall deformation during the unrest, and the other is between November, 2004, to March, 2005, which represents the deformation during the latter half of the unrest. The results show that the deformation field is well modeled by a dike striking roughly east-west, strike of which is consistent with the regional stress field. Shape of the dike, that is, length, width, and thickness, is not well constrained due to the small amount of deformation, up to 10 mm, and the scarcity of GPS sites, but volume of the dike is well constrained to be 6.82 and 4.63 million cubic meters for the whole period and the latter half, respectively. The estimated depth of the dike tip is roughly 1 km below the sea level; the depth of earthquakes is consistent with a theory of dike-induced earthquakes that they occur near the dike tip due to the stress concentration. However, the comparison of the location of the modeled dike and the distribution of earthquakes clearly shows that the earthquake distribution is inconsistent with the theory described above, that is, the earthquakes are distributed only in the eastern half of the modeled dike tip. The possible reasons for this inconsistency are either 1) earthquakes exists in the west half of the dike tip as well, but they are not detected due to the sparse distribution of seismometers to the west of the flank, 2) the western half of the modeled dike is not capable of generating earthquakes because the temperature is too high for brittle failure of rocks, or 3) the differential stress in the western half is so low that the area cannot reach the critical stress field even by the introduction of dike-tip stress concentration. Current geophysical observation cannot identify the reason but future development of geophysical network is expected to solve the puzzle.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 7280 Volcano seismology (8419)
DE: 8185 Volcanic arcs
DE: 8419 Volcano monitoring (7280)
DE: 9320 Asia
SC: Geodesy [G]
MN: Fall Meeting 2005