利用淺層反射震測探討米崙臺地之地下構造;Imaging Subsurface Structure of the Milun Tableland from a Shallow Seismic Reflection Survey

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题名:	利用淺層反射震測探討米崙臺地之地下構造;Imaging Subsurface Structure of the Milun Tableland from a Shallow Seismic Reflection Survey
作者:	鍾育晴;Chung, Yu-Ching
贡献者:	地球科學學系
关键词:	米崙斷層;反射震測;米崙台地;開花構造;Milun Fault;Seismic Reflection Survey;Milun Tableland;Positive Flower Structure
日期:	2021-07-21
上传时间:	2021-12-07 11:46:35 (UTC+8)
出版者:	國立中央大學
摘要:	米崙臺地(Milun Table)位於花東縱谷最北端，其西側以米崙斷層(Milun Fault)為界。米崙斷層為第一類活動斷層，陸地上北起七星潭海岸、南至花蓮市美崙山西南側，前人研究為左移兼具逆移性質，約呈南北走向。先前的學者根據米崙臺地的地型特徵，認為米崙臺地上存在其他的次要斷層，包括民意斷層、七星潭斷層和南濱斷層等，曾有人提出這些次要斷層為米崙斷層活動造成的壓縮型開花構造(Positive Flower Structure)，但由於這些斷層近期的活動構造並不明顯，所以無法了解斷層的特性與地下分布幾何形態，故本研究測線橫跨米崙斷層、米崙臺地北邊並探測這些次要構造的幾何特徵及其活動性質。本研究團隊於 2019 年 5 月，以震盪震源車(Mini Vib)為震源，在花蓮七星潭沿岸區域施測反射震測測線。利用 240 波道系統收集訊號，以共同深度點(Common Depth Point, CDP)概念整理並進行資料處理，震測剖面深度可達約 3 秒，解析深度約 1 秒(約 1 公里)。研究結果顯示七星潭震測測線可看到米崙斷層北邊出海口位置及其上盤背斜構造，並從地下構造中可看見因擠壓而產生的斷裂面，呈現典型的開花狀構造特徵。 ;The Milun Tableland bounded on the west by the Milun Fault is located at the northernmost Longitudinal Valley based on the geological survey. The Milun Fault is considered as an active fault, which starts from the Qixingtan coast in the north to the southwest of Meilun Mountain in Hualien City in the south. Previous studies have showed that the Milun Fault is a left-lateral strike-slip active fault, with a nearly north-south strike. Also, based on the topographic characteristics of the Milun Tableland, there were other secondary faults on the Milun Tableland, including the Mingyi, Qixingtan, and Nanbin faults. It has been proposed that this secondary faults are Positive Flower Structures caused by the activities of the Milun Fault, but few geophysical data exist to show the characteristics and the geometry of the subsurface distribution of the Milun fault. Therefore, in this study, a seismic reflection profile located at the north end of the Milun Tableland along the north coastline was planned and conducted across the Milun fault to explore the geometric features of this fault zone. The seismic field work was conducted in May 2019 with the Mini Vib truck as the seismic source and a 240-channel system with a 4 m geophone spacing as the receiver. The length of the seismic profile is around 2.5 km. The deepest seismic reflectors in this study can be observed around 1 second two-way travel time (around 1 kilometer). As a result, four seismic reflectors (unconformities) and sevral faults can be picked up in the profile and an anticline is observed beneath the Milun Tableland. Based on the geometry of faults and unconformities, this region is under compression with a typical flower structure and been through significant deformation.
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