HR: 0800h
AN: T11D-1300    [Abstracts]
TI: Three Sequential Ruptures Along the Rueisuei Segment of the Longitudinal Valley Fault, Eastern Taiwan
AU: * Fengler, K P
EM: keegan@geology.cwu.edu
AF: Central Washington University, Department of Geological Sciences 400 E University Way, Ellensburg, WA 98926 United States
AU: Rubin, C M
EM: charlier@geology.cwu.edu
AF: Central Washington University, Department of Geological Sciences 400 E University Way, Ellensburg, WA 98926 United States
AU: Chen, W
EM: wenshan@ms.cc.ntu.edu.tw
AF: National Taiwan University, Department of Geosciences 245 Choushan Road R301, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: National Taiwan University, Department of Geosciences 245 Choushan Road R301, Taipei, 106 Taiwan
AU: Madden, C L
EM: madden@earthconsultants.com
AF: Earth Consultants International, 150 El Camino Real, Suite 212, Tustin, CA 92780 United States
AB: The Mw 7.1 1951 October and November earthquakes in eastern Taiwan were the most destructive earthquakes in the past 100 years along the Longitudinal Valley fault. Although these earthquakes produced a substantial amount of damage, little is known about fault slip rates and recurrence intervals along the Longitudinal Valley fault. The November earthquakes produced about 65 km of surface rupture along three north-south trending fault segments along the Longitudinal Valley. During the earthquake, vertical offsets across the faults averaged 1.0 m, with a maximum of 2.1 m. Between June 2003 and February 2004, we initiated paleoseismic studies along the Rueisuei segment of the Longitudinal Valley fault at the Anding bridge site in order to determine the precise timing and magnitude of past earthquakes. Excavations along the 1951 surface rupture reveal evidence of two prehistoric earthquakes. Accelerator mass spectrometer (AMS) radiocarbon ages of detrital charcoal from alluvial deposits and fault scarp colluvium indicate that the penultimate earthquake occurred about 1640 - 1800 AD. The event horizon of the penultimate earthquake is bracketed between two alluvial deposits separated by buried colluvium. Trench wall exposures also revealed clear evidence of at least one pre-1500 AD rupture at the Anding bridge site. AMS dates on detrital charcoal fragments indicate some recycling of detrital charcoal. Vertical offset from the 1951 earthquake at the Anding bridge site was about 1.3 m. Because the scarps formed by the two prehistoric ruptures are similar in height to the scarp formed by the 1951 Mw 7.1 earthquake, the prehistoric ruptures was, at least locally, similar in size to the most recent event. The average dip slip inferred from vertical offset and the observed fault dip of ~27ø for the Longitudinal Valley fault at the Anding bridge during the past three earthquakes was about 6.1 ñ 0.2 m, which implies a dip slip rate of ~10 mm/a. This rate is only 1/2 of the GPS geodetically determined shortening rate across the valley. Although the Longitudinal Valley fault currently creeps at about 10 mm/a, it is clear that the current creep rate does not fully release strain accumulation along the Rueisuei segment.
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting