HR: 1330h
AN: T12C-0480    [PDF]
TI: How to explain the coseismic slip distribution of the 1999 Chi-Chi (Taiwan) earthquake ?
AU: * Cattin, R
EM: cattin@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Loevenbruck, A
EM: loeven@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Le Pichon, X
EM: lepichon@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Le Pichon, X
EM: lepichon@geologie.ens.fr
AF: College de France, 6 place Marcelin Berthelot, Paris, 75005 France
AB: The Chi-Chi 1999 earthquake ruptured the out-of-sequence Chelungpu Thrust Fault (CTF) in the fold-and-thrust belt in Western Central Taiwan. An important feature of this rupture is that the calculated slip increases approximately linearly in the SE-NW convergence plate direction from very little at its deeper edge to a maximum near the surface. Taking into account the dip angle of the CTF, asperity dynamic models can qualitatively explain the general features of coseismic slip distribution. In particular, recent works show the importance of heterogeneous spatial distribution of stress prior to the Chi-Chi earthquake. However our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity. We propose here an alternative explanation based on the study of both stress and displacement over the long term as well as over a seismic cycle. Over the last 0.5 Myr the convergence rate in the mountain front belt is accommodated by the frontal Changhua Fault (Ch.F), the CTF and the Shuangtung Fault (Sh.F). Based on previously published balanced cross sections we estimate that the long term slip of the Ch.F and of the CTF accommodate 5-30 % and 30-55 % of the convergence rate, respectively. This long term partioning of the convergence rate and the modeling of interseismic and postseismic displacements suggest that the peculiar linear coseismic slip distribution is accounted for by a combination of the effect of the obliquity of the CTF to the direction of interseismic loading, and of increasing aseismic creep on the deeper part of the Ch.F and CTF.
DE: 7230 Seismicity and seismotectonics
DE: 8110 Continental tectonics--general (0905)
DE: 8123 Dynamics, seismotectonics
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting