The Mechanics Study of Accretionary Wedge Offshore Southern Taiwan

Friday, 19 December 2014
Ya-Tong Lai, NTNU National Taiwan Normal University, Taipei, Taiwan, En-Chao Yeh, NTNU National Taiwan Normal University, Department of Earth Sciences, Taipei, Taiwan and Char-Shine Liu, NTU National Taiwan University, Taipei, Taiwan
The strengths of decollement, megathrust and accretionary wedge in the subduction zone system are difficult to constrain and there is ongoing debate over the controlling mechanisms and stress magnitudes. In the Manila subduction zone south of Taiwan, previous studies have reported that a major megathrust is present in the accretionary wedge. This study analyzed one large-offset seismic profile MGL0908-23 collected during the TAIGER survey in 2009 to investigate the deep structures of the Manila subduction zone..

Radon filter and eigenvector filter are applied to eliminate the multiples on the seismic profiles, iterative migrate velocity analysis are performed to produce correct velocity structures, and pre-stack depth migration (PSDM) profile is generated to provide better seismic images. Based on the sea floor slope α and the detachment dip β, the morphology of accretionary wedge is determined. Also, fluid retention depth is constrained by the velocity structure. Controlling factor of shape of Manlia subduction zone is investigated via the critically heterogeneous Coulomb wedge theory.

Our seismic profile shows that the accretionary wedge can be further divided into a lower slope domain and an upper slope domain separated by a megathrust. The velocity structure is in accordance with seismic profile structure and provides the information of time-depth correlation. The sea floor slope far away from both deformation front and megathrust becomes gentler. If the detachment dip β is constant, the morphology of accretionary wedge can be controlled by the stronger wedge strength or weaker faults strength. Detailed analysis is needed to test different.