HR: 13:40h
AN: T33E-01 INVITED     [Abstracts]
TI: Structural control on the 2004 Mid-Niigata Prefecture earthquake and its implication for inversion tectonics along NE Japan backarc
AU: * Okamura, Y
EM: okamura-y@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Ishiyama, T
EM: t-ishiyama@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Yanagisawa, Y
EM: y.yanagisawa@aist.go.jp
AF: Institute of Geoinformation and Geoscience, GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AB: The 2004 Mid-Niigata Prefecture earthquake (Mj=6.8) occurred in fold and thrust belts along the eastern margin of Japan Sea. Dense seismic network deployed immediately after the earthquake showed detailed distribution of aftershocks and velocity structure in the source area (e.g. Kato et al. 2005). These seismological studies showed that the source fault of the earthquake is closely related to the geologic structure. The source area is located in one of the Miocene rift basins along the eastern margin of Japan Sea. Many of the rift basins began to uplift due to reactivation of normal fault as reverse faults since late Pliocene. The Higashiyama and Uonuma hills, the source area of the earthquake, are a anticlinorium 15-20 km wide trending in NNE-SSW direction and are composed of Neogene sedimentary sequences. Several discontinuous anticlines of different divergence have been growing during the last a few million years in the anticlinorium. The late Pliocene to early Pleistocene Uonuma Group is the youngest marine sediments which has been uplifted several hundred meters. In the source area of the earthquake, east-vergent asymmetric anticlines have grown but surface faults have not been clearly defined. The subsurface fault which caused the anticlines was inferred assuming that the anticlines in the source area are fault-related folds above a single reverse fault cutting through the upper crust. The inferred fault consists of a deeper steep and an shallower gentle parts with a large bend at about 5 km deep. This geometry of the fault nearly agrees with the source fault of the main rupture imaged from aftershocks. In addition the southern and northern ends of the source area roughly coincide with the lateral extent of the east vergent anticlines in the Higashiyama and Uonuma hills. These comparisons between the source fault of the earthquake and geologic structure support that the 2004 earthquake was a one of the rupture which have been repeating along the same reverse fault below the Higashiyama and Uonuma hills for a few million years.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8005 Folds and folding
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8102 Continental contractional orogenic belts and inversion tectonics
SC: Tectonophysics [T]
MN: Fall Meeting 2005