HR: 0800h
AN: T51A-1329    [Abstracts]
TI: Stress state and potential fault planes in a deflexed lithosphere
AU: * Yang, K
EM: 155055@cpc.com.tw
AF: Chinese Petroleum Corporation, 1 Ta Yuan, Wen Shan, Miaoli, 36010 Taiwan
AU: Wu, J
T51A-1329 AF: Chinese Petroleum Corporation, 1 Ta Yuan, Wen Shan, Miaoli, 36010 Taiwan
AU: Ting, H
T51A-1329 AF: Chinese Petroleum Corporation, 1 Ta Yuan, Wen Shan, Miaoli, 36010 Taiwan
AB: The foreland basin in western Taiwan, which is bordered by a westward moving fold-and-thrust belt to its east, has been developing on a previously extensional margin. Inversion structures can be observed ubiquitous in the entire foreland belt. However, pre-existing normal faults react to the inversion tectonics in different ways in different segments of the foreland belt; some have been reactivated and inverted into high-angle thrust, while some remain as normal faults under the inversion tectonics. Various mechanical models have been proposed to explain the normal fault reactivation. This study attempts to propose another approach to investigate the stress state within a deflected lithosphere. In solving the problem of a deflexed lithosphere, the lithosphere is regarded as a bent plate under vertical loads. Different profiles of deflection can be obtained by solving the governing equation with different loading geometry and boundary condition for the loaded plate. In general, the distributed lifting force would act on the bottom of the deflexed lithosphere. The lifting force is the result from two components, one due to the resistance from the displaced mantle material below and the other due to sediments on the deflexed lithosphere. The opposing acting forces would induce normal stresses on the upper and lower boundaries separately. In this study, an Airy function as the solution of biharmonic equation was sought to calculate the trajectories of the principal stresses and the potential fault planes in a deflected lithosphere. The results show the trajectories of the principal stress and the conjugate potential fault planes in the segment of the lithosphere from the toe of the vertical loads to the crest of forebulge. Rigidity of the deflexed lithosphere affects the geometry of the curved stress trajectories. Because of the curvature of stress trajectories curved fault planes would be induced and the sense of displacement may change gradually along a fault plane. The maximum principal stress changes from horizontal to vertical alternatively from the point acted by the vertical load to the distal area. Therefore, in some places, especially the proximal part, conjugate normal and upthrust faulting occur. This may give an explanation for the different degree in reactivating normal faults during the orogeny. Contour of maximum shear stress also shows that the magnitude decreases from the point where the vertical load is applied.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8010 Fractures and faults
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005