Investigating Occurrence of the Deformation Front Offshore Miaoli, Taiwan

• Main Authors: Pei-Shan Chiang, 江珮姍
• Other Authors: 宋國士
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/59785998901271015165

碩士 === 國立臺灣大學 === 海洋研究所 === 104 === Taiwan is located at the junction of the Eurasian Plate and the Philippine Sea Plate. Because of arc-continent collision occurred in Taiwan Orogeny, resulting in that the western Taiwan has formed series of thrusts aligned in north-south direction. From the Central Mountain Range to the west, the thrust faults are getting younger, and the angle of dip is smaller. The two different collisions which created the Sanyi-Pauli Seismic Zone in Taiwan, and the seismic zone is the product of Taiwan Orogeny. The seismic distributed map in Taiwan in recent years pointed out that Sanyi-Puli Seismic Zone has extended to offshore Miaoli. This evidence also indicated that the stress of Taiwan Orogeny has reached offshore Miaoli. We collected three different sonar data, the multi-beam echo system, the side-scan sonar system, and a Boomer reflection system in offshore Miaoli. The regional topography ranged between 6-40 meters depth. There are many paleo dunes on sea floor in the west of the study area. We will explain those dunes by side-scan images and the seismic profiles. Those sand dunes were created by ocean current or tidal current. The reflection seismic profiles suggest that the old dunes were formed in Late Pleistocene. The ocean current caused several sand dunes shown on outer seabed. These sand dunes on the seabed indicated that there are less earthquakes in this area. In addition, the less earthquakes and the small magnitude of earthquakes occurred in past 15 years in offshore Miaoli. In reflection seismic profiles, we totally found six normal faults. Those normal faults were in Toukoshan Formation, representing that this area has been in Taiwan Orogeny. The largest F6 fault and Sanyi-Puli Seismic Zone had same axis orientation. Additionally, the F6 fault had left moving mechanism, and this feature point out that F6 was generated by Sanyi-Puli seismic zone, indicating that the Taiwan Orogeny has been farer than the study area.