HR: 0800h
AN: U11A-0809    [Abstracts]
TI: Aftershock distribution of the December 26, 2004 Sumatra-Andaman earthquake from ocean bottom seismographic observation
AU: * Araki, E
EM: araki@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Shinohara, M
U11A-0809 AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo, 113-0032 Japan
AU: Obana, K
U11A-0809 AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Yamada, T
U11A-0809 AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo, 113-0032 Japan
AU: Kaneda, Y
U11A-0809 AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Kanazawa, T
U11A-0809 AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo, 113-0032 Japan
AU: Suyehiro, K
U11A-0809 AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AB: We conducted deployment of OBS (Ocean Bottom Seismographs) network from February to March 2005 in the rupture area of the Sumatra Andaman earthquake on December 26, 2004. We deployed 17 short-term OBS and two long-term OBSs, and recovered the short-term OBSs after observation for 19 to 22 days. One of the long-term OBSs were recovered in August, 2005. Hypocenter distribution from the 17 OBS network delineated detailed structure of aftershock seismicity in offshore Sumatra Island. Aftershock seismicity associated with subducting slab starts 30km inward from the Sunda trench axis, and ceases at 50km depth beneath the Aceh basin approximately 240km inward from the trench axis. Aftershocks in 120-170km from the trench axis consists a surface with a dip of 10 to 12 degrees dominated by dip-extension type mechanism. Beyond the southwestern edge of the Aceh basin, the aftershock activity becomes higher, and dominated by dip-slip type earthquakes, with a slightly increased dipping angle of 15 to 20 degrees. Three along arc bands of shallow seismicity were identified near the Sumatra trench, 90 km inward from the trench, and in the south of the Aceh basin. These locations correspond to steep topographic slopes in the accretionary prism, suggesting present evolutional activity of accretionary prism offshore Sumatra Island.
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Union [U]
MN: Fall Meeting 2005