The shear-wave velocity structure and characteristic of velocity anisotropy of the Philippine Sea Plate

• Main Authors: Ching-yu Lu, 呂靜渝
• Other Authors: Chau-Huei Chen
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/13307769262134318366

碩士 === 國立中正大學 === 地震研究所暨應用地球物理研究所 === 95 === This research is to use Love waves of far-field earthquakes to determine the crust and upper mantle shear velocity structure of the Philippine Sea plate, and more importantly to investigate the characteristic of velocity anisotropy of the plate. The Hilbert-Huang Transform（HHT）method is used to obtain the dispersion curve of Love wave, and group velocities at different period. And then the back-projection method is applied to determine the velocity structures of crust and upper mantle of the plate. Hence, by using the obtained velocity structure, we are able to determine the magnitude and direction of velocity anisotropy. The results show that there exists relative low velocity at east Philippine Trough、Nankai Trough and Parece Vela Basin. Since these areas located near active plate boundary which exist high heat flow that leads to low velocity observation. The velocity beneath the West Philippine basin is the highest and the Parece Vela Basin is the lowest. This observation is due to the velocity of the geological structure of the West Philippine basin is much older than that at the Parece Vela Basin. At the period of 60 seconds, the corresponding depth is where the Philippine Sea plate has reach the asthenosphere, velocity at the Parece Vela Basin is lower than that observed from shorter period. One of the important results obtain from this study is lateral variation of velocity anisotropy across the Philippine Sea plate, the result indicates that the direction of anisotropy is parallel to the regional tectonic stress. We suggest that the plate is mostly affected by the trench pull force at this current stage. The south east side of the plate, i.e. Parece Vela Basin, is mainly perpendicular with West Mariana Ridge. The driving forces acts on the northern part of the plate is Ryuku Trench pull force. The anisotropic direction in the NW part of the plate is parallel to the direction of island arcs, and at the north side of the plate is in NW direction and then turns to almost in E-W direction. We also find the magnitude of anisotropy is decreased from the NW direction to the SE direction.