HR: 0800h
AN: U11A-0803    [Abstracts]
TI: Deep Tow Sub-bottom Profiler and Side Scan Sonar records around the epicenter of the Sumatra Earthquake, 26th December, 2004
AU: * Arai, K
EM: ko-arai@aist.go.jp
AF: Geological Survey Japan AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Iba 308-8567 Japan
AU: Kisimoto, K
U11A-0803 AF: Geological Survey Japan AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Iba 308-8567 Japan
AU: Ikehara, K
U11A-0803 AF: Geological Survey Japan AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Iba 308-8567 Japan
AU: Joshima, M
U11A-0803 AF: Geological Survey Japan AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Iba 308-8567 Japan
AU: Nishimura, K
U11A-0803 AF: Geological Survey Japan AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Iba 308-8567 Japan
AU: Soh, W
U11A-0803 AF: Japan Agency for Marine-Earth Science Japan Agency for Marine-Earth Science JAMSTEC, 2-15 Natsushima, Yokosuka, Kan 237-0061 Japan
AU: Machiyama, H
U11A-0803 AF: Japan Agency for Marine-Earth Science Japan Agency for Marine-Earth Science JAMSTEC, 2-15 Natsushima, Yokosuka, Kan 237-0061 Japan
AB: 26th December 2004, a great Sumatran Earthquake and its subsequent devastating Tsunami attacked not only the Sumatra Island but also many countries which face to the Indian Ocean. The epicenter was located at off Simuelur Island, off Aceh, northern Sumatra, Indonesia. The seismic rupture was propagated northward along the Nicobal and Andaman Islands more than 1,000 km long. Urgent offshore survey program (NT05-2 Natsushima cruise) was carried out by the JAMSTEC and the BPPT in order to examine geomorphological changes and to monitor aftershocks in and around the overriding plate off Ache, Sumatra, Indonesia. The swath bathymetry survey by the multi-beam echo sounder and the single channel seismic (SCS) profiles indicated the thrust ridge and landmass wasting patterns. Near-bottom observations were carried out successfully by the ROV, Hyper Dolphin, to find abundant deformed features of the seafloor, such as ruptures and fissures. The speculation onboard is that some of the observed deformation on the seafloor surface was co-seismic, possibly caused by exceeding gravity acceleration during the grand motion of the catastrophic earthquake. The DAI-PACK (Deep-sea Acoustic Imaging Package) which is composed of Deep-sea Sub-bottom Profiler (SBP) and Side Scan Sonar (SSS) systems was piggybacked on the ROV Hyper Dolphin to clarify the deformation and faulting below/on the seafloor. The DAI-PACK system is designed to get high-resolution acoustic profiles and imageries of the seafloor. The SBP uses 10kHz transducer, capable of 6 cm vertical resolution with subbottom penetration of up to 40 m. The SSS uses 300kHz transducers for imaging the seafloor. Bottom penetration of SBP was from 10 to 20 meters throughout the NT05-2 cruise. We found stratified sediment broken into large clumps at the foot of steep slope of the thrust ridge during the ROV Dive 386. Strong reflectors occur in the steep slope area and some strata tilted to landward covered with thin soft sediment. On the top of the thrust ridge, we saw many ruptures and fissures in video images of ROV from the Dive 391. The SSS imagery of the fissure/rupture shows strong reflectors and structural patterns. The SBP image shows that the sediments above the strong reflector at about 7.5 m is highly deformed in general. Strong reflector at about 9 m depth can be traced continuously below the deformed strata. We could not identify a thrust rupture on the seafloor, however, very intense earthquake shaking was inferred from the deformed features on the young sediments at the top of thrust ridge.
DE: 3080 Submergence instruments: ROV, AUV, submersibles
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8010 Fractures and faults
DE: 9340 Indian Ocean
SC: Union [U]
MN: Fall Meeting 2005