HR: 1340h
AN: S23B-0237    [Abstracts]
TI: A Triple Junction of Plates and Tectonics in Hokkaido, Japan Using Local Seismic Tomography
AU: * Kim, S
EM: sogukim@hanmail.net
AF: Hanyang University, Sa-dong, Ahnasnshi, 425791 Korea, Republic of
AU: Bae, H
EM: baehs79@hanmail.net
AF: Hokkaido University, N10 W8 Kita-ku, Sapporo, 0600810 Japan
AU: Kasahara, M
EM: mkasa@eos.hokudai.ac.jp
AF: Hokkaido University, N10 W8 Kita-ku, Sapporo, 0600810 Japan
AU: Ichianagi, M
EM: yanamasa@eeos.hokudai.ac.jp
AF: Hokkaido University, N10 W8 Kita-ku, Sapporo, 0600810 Japan
AB: Abstract: Three-dimensional tomography (Kim et al., 2004) was applied to 64,024 P-wave travel times and 64,618 S-wave travel times observed at 238 seismic stations for 4050 local earthquakes in the depth range of 0 to 300 km in and around Hokkaido, Japan. Vp/Vs ratio discrepancies (VRD) were clearly imaged in and around Hokkaido. The upper seismic planes of the double seismic zone (DSZ) were found in the subducted Pacific Plate beneath Hokkaido at a depth of 40-80 km, which produced high seimicity in and around Hokkaido. The findings of high Vp/Vs ratio discrepancies beneath the Moho discontinuity supports an evidence of a surface triple-collision hypothesis proposed by Moriya (1994) which states that the Kuril Arc (Okhotsk Plate or North American Plate) is colliding against the NE Japanese Arc (Amurian Plate or Eurasian Plate), along and beneath the Hidaka Mountain Range, and at the same time the Pacific Plate is subducting into these two plates, making for "an equilibrium of tectonic forces" along the Hikada Mountain Range (HMR) corner and the central tectonic axis (142-143 E) in Hokkaido. The low Vp and Vs values were also found east and west along the central tectonic axis in which the focal mechanism represents the extensional forces. These phenomena are also consistent with low Bouguer gravity anomalies in this region. Most great earthquakes occurred outside Hokkaido with the "break-up" of the balance of the three tectonic forces exerted on the plate juncture in Hokkaido. Keywords: VRD, double seismic zone, Bouguer gravity 1. Tectonophysics and Crustal Structure 2. VRD, double seismic zone, Bouguer gravity
DE: 6982 Tomography and imaging (7270, 8180)
DE: 7270 Tomography (6982, 8180)
DE: 7280 Volcano seismology (8419)
DE: 7290 Computational seismology
DE: 8180 Tomography (6982, 7270)
SC: Seismology [S]
MN: Fall Meeting 2005