HR: 14:40h
AN: T33E-05    [Abstracts]
TI: Millennial Slip Rate of the Longitudinal Valley Fault From River Terraces: Implications for Convergence Across the Active Suture of Eastern Taiwan
AU: * Shyu, J H
EM: jbhs@gps.caltech.edu
AF: Tectonics Observatory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 United States
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: Tectonics Observatory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 United States
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Tectonics Observatory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 United States
AU: Chen, W
EM: wenshan@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei, 106 Taiwan
AB: Interpreting a geomorphic analysis of fluvial terraces in the hanging-wall block of a major active fault in Taiwan by means of a structural model, we have created a model for the creation of a lithospheric suture that may have broader application. The Longitudinal Valley fault is a key element in the active tectonics of Taiwan. It is the principal structure accommodating convergence across the eastern of the two active sutures of the Taiwan orogeny. To understand more precisely its role in the suturing process, we analyzed fluvial terraces along the Hsiukuluan River, which is the only river that cuts across the Coastal Range of eastern Taiwan, in the hanging-wall block of the Longitudinal Valley fault. This allowed us to determine both the subsurface geometry and the millennial slip rate of the fault. The uplift pattern of the Hsiukuluan River terraces is consistent with a fault-bend fold model. Our analysis yields a listric geometry for the Longitudinal Valley fault in its uppermost 2.5 km, with dips decreasing downdip from about 50° to about 30°. The maximum dip-slip component of the Holocene slip rate of the fault is about 23 mm/yr, which yields a maximum horizontal shortening rate of about 25.6 mm/yr in the direction of plate convergence. This rate is far less than the 40 mm/yr rate of shortening across the Longitudinal Valley derived from GPS measurements. The discrepancy may reflect an actual difference in millennial and decadal rates of convergence. An alternative explanation, however, is that the discrepancy is accommodated by a combination of subsidence of the Longitudinal Valley and slip on the Central Range fault, the other active fault of the suture. The shallow listric geometry of the Longitudinal Valley fault at the Hsiukuluan River valley differs markedly from the deep listric geometry illuminated by earthquake hypocenters near Chihshang, about 45 km to the south. We propose a model whereby this fundamental along-strike difference in geometry of the fault is a manifestation of the northward maturation of the suturing of the Luzon volcanic arc to the Central Range continental sliver. We believe that this model, in which the development of a complex, "Christmas tree" pattern of progressively active faults between the two crustal blocks may be a characteristic way that suture zones form. The actively suturing Taiwan orogen may thus provide an insight for interpreting old sutures.
DE: 8015 Local crustal structure
DE: 8107 Continental neotectonics (8002)
DE: 8150 Plate boundary: general (3040)
DE: 8175 Tectonics and landscape evolution
DE: 9320 Asia
SC: Tectonophysics [T]
MN: Fall Meeting 2005