HR: 0800h
AN: T41B-1299    [Abstracts]
TI: Deformational Mechanism of Upper Cenozoic System in the Epicentral Area of the 2004 Mid-Niigata Prefecture Earthquake, Central Japan: Insights from Physical Modeling
AU: * Ueta, K
EM: ueta@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194 Japan
AU: Inoue, D
EM: daiei@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194 Japan
AU: Torigoe, Y
EM: W910743@tohoku-epco.co.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194 Japan
AB: Physical experiments were performed to gain a better understanding on the deformational mechanism of the upper Cenozoic system in the epicentral area of the 2004 Mid-Niigata Prefecture earthquake (MJMA 6.8), Japan. The present study focuses on deformation of sedimentary cover, including overpressured mudstone, caused by reverse movements along the basement fault corresponding to the source fault responsible for the main shock. Our physical models comprise dry quartz sand representing brittle sedimentary rock and viscous silicone polymer representing overpressured mudstone. Computerized X-ray tomography to analyze the kinematic evolution and geometry of folds and faults in the models indicates that minor folds and minor displacement out-of-syncline thrusts developed on the footwall of the major monoclinal flexure within the sedimentary cover above the steeply dipping reverse basement fault. The out-of-syncline thrust diverged from the flexural-slip fault that is parallel to the horizon between sand layer and silicone polymer layer. These results compare well with the geometry and kinematic evolution of geologic structure in the epicentral area. Minor folds distribute on the footwall of the major monoclinal flexures. These folds are interpreted as minor folds developed during formation of the major monoclinal flexure propagating from the steeply dipping reverse basement fault, which corresponds to the source fault responsible for the main shock. The thrust beneath the surface rupture associated with the earthquake is inferred to be the out-of-syncline thrust diverging from the flexural-slip fault that runs along a certain overpressured mudstone layer. Overpressured mudstone and gravity sliding within the sedimentary cover may play important roles for the development of these geologic structures in the epicentral area.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: Fall Meeting 2005