HR: 12:00h
AN: T32C-07    [Abstracts]
TI: The latest event and start period of the thrust system in the Kuromatsunai lowland, northernmost part of the back arc zone of Northeast Japan
AU: * AZUMA, T
EM: t-azuma@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, Central 7, 1-1-1, Higashi, Tsukuba, 3058567 Japan
AU: GOTO, H
EM: hgoto@educ.fukushima-u.ac.jp
AF: Fukushima University, 1, Kanayagawa, Fukushima, 9601296 Japan
AU: OKUMURA, K
EM: kojiok@hiroshima-u.ac.jp
AF: Hiroshima University, 1-2-3, Kagamiyama, Higashi-Hiroshima, 7398522 Japan
AU: SUGIYAMA, Y
EM: sugiyama-y@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, Central 7, 1-1-1, Higashi, Tsukuba, 3058567 Japan
AB: The Kuromatsunai-teich fault zone is an N-S trending fold and thrust zone in southwestern Hokkaido. Kuromatsunai lowland is located in the northernmost area of the fold and thrust zone in the back arc of Northeast Japan. Only few data had been obtained for the active faults in Hokkaido. We made trenching surveys and seismic profiling in this fault zone and obtained new data on the timing of the latest faulting events and the subsurface structures. The results of trench and pit excavation surveys at two sites (Shirozumi and Warabitai) show the latest event occurred after the Last Glacial period. At the Warabitai site, the timing of the latest faulting was narrowed down around 5,500 yBP. The results of seismic profiling on two lines show westward tilting. The westward dip of the layers decrease upward and the thickness of each layers increases toward the axis of syncline. This indicates the growth of tilting through the Middle to the Late Quaternary period. Based on the tilting rates of the late Pleistocene terraces, the deformation in this fault zone was informed to have started Early to Middle Pleistocene period (ca. 0.8 Ma).
DE: 9320 Asia
DE: 7221 Paleoseismology
DE: 7230 Seismicity and seismotectonics
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting