HR: 1340h
AN: T13C-1397    [Abstracts]
TI: Seismic reflection profiling of the fault related fold in the eastern margin of the Japan Sea
AU: * Abe, S
EM: shintaro@criepi.denken.or.jp
AF: CRI of Electric Power Industry, Abiko 1646, Abiko-shi, Chiba-ken, 270-1194 Japan
AB: The fault related fold in the eastern margin of the Japan Sea was investigated to evaluate its activity by geomorphologic and geological surveying. The investigated area is Japan sea off the Tsugaru peninsula where a 16 km long fault related fold had been shown in the previous tectonics map. The submarine geomorphology of the area was mapped by a narrow multi beam survey. In addition roughness and materials of the seafloor were imaged by a side-scan sonar survey. The synthetic picture of these results revealed a geomorphologic character of the continental shelf. A small valley passes through and runs on the axis of anticline from the continental shelf to the continental slope was found. The intensity of reflection on the axis of anticline is high. It seems that the old stratum is exposed. The three dimensional geological structure of a several hundred meters depth below seafloor was clarified by seismic reflection surveys using chirp sonar and water gun. The former target is stratigraphy in shallow part and the latter one is deeper structure. In order to acquire high horizontal resolution and to operate following digital filtering, a short shot-interval and digital recording were applied in the survey. The survey lines run across the investigated area in every 500 meters and along it in every 1000 meters. A thick sedimentary layer of middle Pleistocene was confirmed with reference to the following piston coring and the past exploration drilling in the survey area. The gravity piston cores were sampled at 8 points across the anticline to clear geological age of the acoustic layers. In evaluation of the fault related fold activity, the kink bands around the forelimb were observed on the seismic profiles. The growth pattern of the kink band is identified to hinge migration with a constant dip. As a result of tracing the deformed layer across the dense profiles, two folds were identified in the area, which had been recognized as a long fold in the previous studies. Besides, the upper limit of the deformed layer has the partial variation along the fold.
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8005 Folds and folding
DE: 8015 Local crustal structure
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting