HR: 11:55h
AN: T11F-07    [PDF]
TI: Prehistoric Earthquakes Along The Sanchiao Fault, Taipei Basin, Northern Taiwan
AU: * Huang, S
EM: queens@geology.cwu.edu
AF: Department of Geological sciences, Central Washington University, 400 E 8th Ave, Ellensburg, WA 98926 United States
AU: Rubin, C M
EM: charlie@geology.cwu.edu
AF: Department of Geological sciences, Central Washington University, 400 E 8th Ave, Ellensburg, WA 98926 United States
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Liu, H
EM: liuhc@linx.moeacgs.gov.tw
AF: Central Geological Survey, 2. Lane 109, Hua-Hsin Street, Chung-Ho, Taipei, 235 Taiwan
AU: Su, T
EM: david@linx.moeacgs.gov.tw
AF: Central Geological Survey, 2. Lane 109, Hua-Hsin Street, Chung-Ho, Taipei, 235 Taiwan
AU: Lai, T
EM: hua@linx.moeacgs.gov.tw
AF: Central Geological Survey, 2. Lane 109, Hua-Hsin Street, Chung-Ho, Taipei, 235 Taiwan
AU: Chiu, C
EM: chiucl@linx.moeacgs.gov.tw
AF: Central Geological Survey, 2. Lane 109, Hua-Hsin Street, Chung-Ho, Taipei, 235 Taiwan
AB: Although numerous large earthquakes in Taiwan have produced surface rupture during the last century, little is known about fault slip rates and recurrence intervals of fault displacement in metropolitan Taipei city. Previous studies along the Sanchiao Fault, a major normal fault that flanks the western boundary of the Taipei Basin, suggest that the fault has a long-term slip rate of ~2.3mm/yr for the past 400,000 years. The Sanchiao Fault cuts the Quaternary Sunshan Formation and contains evidence for the age of subsidence of Taipei Basin. Strata from eight boreholes were examined in order to document the late-Pleistocene-Holocene record of earthquakes along the fault. Grain size analysis, total carbon content, lithology, texture, sedimentary structures, paleosols and fossil abundance were used to correlate subsidence stratigraphic units. Woody material and detrital charcoal from the boreholes were processed to provide radiocarbon dates. Borehole SCF05 and SCF06, drilled at the northern section of the fault, show two stages of hanging wall thickening. The amount of net offset between SCF05 and SCF06 abruptly changes from 5 to 8m, implying rapid subsidence of about 3 meters at about 9.3~9.4 kyr B.P. Similarly, net offset between SCF05 and SCF06 abruptly changes about 2 m occurs at about 11.1 kyr B.P., suggesting rapid subsidence. Borehole SCF01 and SCF02, located at the central section of the Sanchiao Fault, also display similar thickening and rapid subsidence. The net offset between SCF01 and SCF02 abruptly changes from 8 to 12m, suggesting rapid subsidence of about 4 m at about 8.4~8.6 kyr B.P. Earlier subsidence at about 8.9~9.1 kyr B.P. records similar displacement. Borehole SCF14, SCF15, SCF16 and SCF17, located at the southern section of the fault and do not show substantial Holocene offset. According to our subsurface stratigraphic correlations, we suggest that the Sanchiao Fault generated episodic earthquakes during the past 10,000 years. The amount of vertical offset for each event ranges from 2 to 4.8m. If we assume that 3.5m offset represents the average surface displacement, simple scaling relationships between surface displacement to moment magnitude yields a Mw 7.1 earthquake. Damage from large magnitude earthquakes along the Sanchiao Fault would be substantially different from that produced in the 1999 Mw 7.6 Chi-Chi earthquake. A large magnitude earthquake on the Sanchiao fault would rupture eastward, directing energy into the densely populated basin.
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting