Active deformation of coastal and fluvial terraces by the blind Miaoli frontal structure in the Miaoli coastal area, western Taiwan

• Main Authors: Yu-Wei Yuan, 袁宇威
• Other Authors: 徐澔德
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/8m974d

碩士 === 國立臺灣大學 === 地質科學研究所 === 106 === The island of Taiwan is located at the convergent boundary between the Eurasian and the Philippine Sea plates. The ongoing collision between the Luzon arc and the Eurasian continental margin produced the Taiwan mountain belt. In the Miaoli area in northwestern Taiwan, the hilly area extends all the way to the coast, suggesting that this area is influenced by tectonic activities. However, no active fault has been officially proposed in this area. Previous studies have not paid attention to structural activities in this area either. Therefore, this study analyzed the terraces in the Miaoli coastal area to understand the active structures and their activities. This study focuses on the coastal area between the Houlong River and the Daan River. We analyzed the terrace distributions to study the relationship between the formation of terraces and structural activities, and observed the terrace deposits and bedrocks in outcrops and trenches. The wide spread terraces in this area suggest that the entire area is uplifted by the activity of a proposed Miaoli frontal structure. We constructed the subsurface geometry of this structure with bedrock and geomorphology observations, and calculated the slip rate of this structure with terrace sediment dating results. Based on the observation, the terraces are also deformed by the activity of two other structures, the Futokeng fault and a secondary Daotichi structure. Based on the observations of GPS analysis and seismic profiles, we suggest that the structural development of the Miaoli frontal structure is related with the general structural evolution of the Hsinchu and Miaoli area, and the southward propagation of collision in Taiwan. The Futokeng fault may cut through the Miaoli frontal structure in the future and become one of the main active structures in this area. Based on the results of the terrace sediment dating, many structures in this area can be considered as active structures. Therefore, it is important to consider future earthquake hazards of these structures.