HR: 1330h
AN: T12C-0474    [PDF]
TI: Reevaluation of 1935 M 7.0 earthquake fault, Miaoli-Taichung Area, western Taiwan: a DEM and field study
AU: * Lin, Y N
EM: b87305139@ntu.edu.tw
AF: Inst. of Geoscience, NTU, No. 1, Sec. 4th, Roosevelt Rd., Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Inst. of Geoscience, NTU, No. 1, Sec. 4th, Roosevelt Rd., Taipei, 106 Taiwan
AU: Ota, Y
EM: ota@iceice.com
AF: Yokohama U., 2-11-13-201, Minamisenzoku, Otaku, Tokyo, 240-8501 Japan
AB: A large earthquake (M 7.0) took place in Miaoli area, western Taiwan on April 21st, 1935. Right to its south is the 1999 Chi-Chi earthquake fault, indicating it is not only tectonically but seismically active. As the previous study, the study area is located in the mature zone of a tectonic collision that occurred between Philippine sea Plate and Eurasia continental Plate. The associated surface ruptures of 1935 earthquake daylighted Tungtsichiao Fault, a tear fault trending NE in the south and Chihhu Fault, a back thrust trending N-S in the north, but no ruptures occurred in between. Strike-slip component was identified by the horizontal offset observed along Tungtsichiao Fault; however, there are still disputes on the reported field evidence. Our purposes are (1) to identify the structural behaviors of these two faults, (2) to find out what the seismogenic structure is, and (3) to reconstruct the regional geology by information given by this earthquake.\\ By DEM interpretation and field survey, we can clearly recognize a lot of the 1935 associated features. In the west of Chihhu Fault, a series of N-S higher terraces can be identified with eastward tilted surfaces and nearly 200 m relative height. Another lower terrace is also believed being created during the 1935 earthquake, showing an east-facing scarp with a height of ca. 1.5~2 m. Outcrop investigation reveals that the late-Miocene bedrock has been easterly thrusted over the Holocene conglomerates, indicating a west-dipping fault plane. The Tungtsichiao Fault cuts through a lateritic terrace at Holi, which is supposed developed in Pleistocene. The fault scarp is only discernible in the northeastern ending. Other noticeable features are the fault related antiforms that line up along the surface rupture. There is no outcrop to show the fault geometry among bedrocks.\\ We re-interpret the northern Chihhu Fault as the back thrust generated from a main subsurface detachment, which may be the actual seismogenic fault. Due to the bend geometry normally existing between ramp and detachment, stress accumulated and earthquake happened right on it. The fault tip of this main thrust may be blind on land or break out offshore, which explains why no surface ruptures related to the main thrust were found.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 7221 Paleoseismology
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting