HR: 14:45h
AN: T13F-05    [Abstracts]
TI: Investigating The Kinematics Of Shortening Across The Pakuashan Anticline, West Central Taiwan.
AU: * Simoes, M
AF: Ecole Normale Superieure - Laboratoire de Geologie, 24 rue Lhomond, Paris, 75005 France
AU: * Simoes, M
AF: California Institute of Technology - GPS division, MC 100-23, Pasadena, CA 91125 United States
AU: Avouac, J
AF: California Institute of Technology - GPS division, MC 100-23, Pasadena, CA 91125 United States
AU: Chen, Y
AF: National Taiwan University - Department of Geosciences, 105R, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Singhvi, A
AF: Physical Research Laboratory - Planetary and Geosciences Division, Navarangpura, Ahmedabad, 380009 India
AU: Chan, Y
AF: Academia Sinica - Institute of Earth Sciences, 128 Academia Road - Sec. 2, Nankang , Taipei, 115 Taiwan
AU: Jaiswal, M
AF: Physical Research Laboratory - Planetary and Geosciences Division, Navarangpura, Ahmedabad, 380009 India
AU: Bernard, S
AF: Ecole Normale Superieure - Laboratoire de Geologie, 24 rue Lhomond, Paris, 75005 France
AB: The Pakuashan anticline is an active fault-propagation fold which constitutes the most frontal zone of deformation along the Western Foothills of central Taiwan. This blind fault is thought to be responsible for the 1848 Changhua earthquake, M~7.1, and to be currently locked. Previous studies mostly based on balanced cross-sections, have suggested various amounts of total shortening varying from 400m to 5km. The shortening rate was poorly constrained due to the uncertainty on this estimate as well as on the age of initiation of folding. Assessing the seismic hazard associated with this fold and its contribution to crustal shortening across central Taiwan, would require some better constraints on the fold structure and growth rate. To address this issue, field investigations allowed surveying the geometry of several deformed strata and geomorphic surfaces which recorded different cumulated amounts of shortening. These units were dated from Optical Stimulated Luminescence, and yielded ages ranging between ~ 19000 yr to ~ 300000 yr. We combined our data with seismic profiles and well logs which provided useful constraints on the deep structure of the fold and on finite deformation. None of the existing models of fault-propagation folding was found successful in reconciling the fold structure with incremental deformation documented from our study. We therefore used a simple analytical formulation which has been obtained recently from sand-box experiments (Bernard, Avouac, and Dominguez, this session). We derived a kinematic model which predicts a finite deformation consistent with the deep structure of the fold, and incremental folding consistent with the deformation of the shallower sedimentary units and geomorphic surfaces. As an outcome, we estimate cumulative shortening across the fold, age of initiation of folding, and the incremental deformation that occurred since the deposition of the various dated units. Consequently, we were able to derive an estimate of the slip rate on the Changhua thrust fault. This approach proved successful in reconciling all data for the Pakuashan anticline and should therefore be applicable widely to determine the kinematics of fault-propagation-folds.
DE: 7223 Seismic hazard assessment and prediction
DE: 8005 Folds and folding
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting