Seismic structure across asperity area of off-Miyagi earthquake,NE Japan using OBSs,Land stations and explosives

HR: 1340h
AN: T33B-0534 [Abstracts]
TI: Seismic structure across asperity area of off-Miyagi earthquake,NE Japan using OBSs,Land stations and explosives
AU: * Watanabe, I
EM: izumi@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Shinohara, M
EM: mshino@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Mochizuki, K
EM: kimi@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Yamada, T
EM: yamada@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Nakahigashi, K
EM: kazuo@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kurashimo, E
EM: ekura@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kato, A
EM: akato@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Iidaka, T
EM: iidaka@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Iwasaki, T
EM: iwasaki@eri.u-tokyo.ac.jp
AF: ERI,Univ.Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Sendai, Miyagi, 980-8578 Japan
AU: Nishino, M
EM: nishino@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Sendai, Miyagi, 980-8578 Japan
AU: Kuwano, A
EM: kuwano@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Sendai, Miyagi, 980-8578 Japan
AU: Yamamoto, Y
EM: yyama@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Sendai, Miyagi, 980-8578 Japan
AU: Takanami, T
EM: ttaka@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Murai, Y
EM: murai@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Machida, Y
EM: machida@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Makino, Y
EM: makino@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Saito, I
EM: ichisuke@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Azuma, R
EM: azoomar@eos.hokudai.ac.jp
AF: Hokkaido Univ., Sapporo, Hokkaido, 060-0810 Japan
AU: Sato, T
EM: satot@earth.s.chiba-u.ac.jp
AF: Chiba Univ., Chiba, Chiba, 263-8522 Japan
AU: Uehira, K
EM: uehira@sevo.kyushu-u.ac.jp
AF: Kyushu Univ., Shimabara, Nagasaki, 855-0843 Japan
AU: Miura, S
EM: miuras@jamstec.go.jp
AF: IFREE,JAMSTEC, Yokohama, Kanagawa, 236-0001 Japan
AU: Fujie, G
EM: fujie@jamstec.go.jp
AF: IFREE,JAMSTEC, Yokohama, Kanagawa, 236-0001 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: IFREE,JAMSTEC, Yokohama, Kanagawa, 236-0001 Japan
AB: In a region off Miyagi, it is suggested that a large earthquake will occur in the near future. Therefore a long-term ocean bottom seismic observation has been performed since 2002. In addition, many seismic surveys using ocean bottom seismometers (OBSs) and controlled sources were carried out. In August 2005, a large thrust-type earthquake (M=7.2) occurred in the estimated source area of future off-Miyagi earthquake. However a detailed seismic structure around the source area is not still obtained due to its depth. In summer 2004, we conducted an intensive seismic refraction/reflection survey using OBSs, land stations and controlled seismic sources such as airguns and explosives in sea and land. The purposes of this experiment are to obtain detailed P- and S- wave velocity structures around the plate boundary including asperities of large earthquakes, and to study amplitude variation of reflected waves from the plate boundary. Three profiles, one is perpendicular to the trench and two are parallel with the trench, pass across the asperities of past and future Off- Miyagi earthquakes. The EW profile ,which has 200km long in the marine area, was extended to the land to obtain a deep structure. Explosives whose charge size was 40 kg were used as seismic sources on the EW line and the trench parallel profile close to land. The EW line had 22 OBS at an average interval of 4 km and 7 land stations. Twenty-one OBSs were deployed on the trench parallel profile at an interval of 15 km. Two dimensional velocity models beneath two profiles were estimated by a 2-D ray tracing method. Beneath the trench parallel profile, an island arc Moho exists about 22-24km deep and P-wave velocity of the uppermost mantle is estimated to be 8.1 km/s. Furthermore, the plate boundary is expected to exist at depth of about 35km using travel times of reflected waves. The refracted waves penetrated through to depth of 25 km below the EW line. The structure deeper than 25 km was determined by reflected waves. The dip angle of the subducting plate estimated from our study is consistent with that of focal solution of the 2005 Off-Miyagi earthquake.
DE: 3025 Marine seismics (0935, 7294)
DE: 3050 Ocean observatories and experiments
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005