Crustal Structures of P-Wave and S-Wave Velocity off Taiwan and Philippine Sea Based on OBS Data (III)

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Project title

Code/計畫編號

MOST104-2611-M019-021

Translated Name/計畫中文名

臺灣及鄰近地區地體動力學研究---子計畫：臺灣與菲律賓海之海底地震儀震測地殼P波與S波速度構造研究 (Ⅲ)

Project Coordinator/計畫主持人

Tan-Kin Wang

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Institute of Earth Sciences

Website

https://www.grb.gov.tw/search/planDetail?id=11585732

Year

2015

Start date/計畫起

01-08-2015

Expected Completion/計畫迄

31-07-2016

Bugetid/研究經費

1304千元

ResearchField/研究領域

海洋科學

本年度將使用過去一年水平層速度分析及重合前深度移位震測剖面(2009年TAIGER航次T4、T5與 T6)建立沉積層P波速度構造。根據上年度完成的重合前深度移位剖面(T4)顯示花東海盆有許多斷層構造且基盤起伏變化大，代表將進入隱沒的複雜構造與呂宋島弧的碰撞相關，向東靠近臺東峽谷附近發現基盤突起及下方的低速帶(3公里/秒），可能為花東海盆上的右移斷層所造成。T5測線沉積物沿著琉球海溝的北邊覆蓋形成增積岩體及加瓜海脊向北隱沒造成的凹槽。西邊橫跨耶雅瑪海脊的南方有較厚的沉積物(4公里），在海底地形突起下方發現高速帶(3.7公里/秒），推測是因T5測線切過琉球海溝（隱沒區域），海底山脊的隱沒所造成。根據重合前深度移位技術建立的沉積層P波速度構造，再結合海底地震儀水壓及垂直分量資料進行走時反演分析跨越花東海盆、加瓜海脊、西菲律賓海盆、琉球海溝、耶雅瑪增積岩體、琉球弧前海盆以及琉球島弧的三條海底地震儀測線，建立地殼P波速度模型。本研究不但以折射初達波及首波訊號分析地殼速度變化，也使用反射波走時解析地殼構造界面。琉球隱沒帶的地體速度構造可探討花東海盆、西菲律賓海盆及琉球弧前海盆沉積物基盤深度變化、加瓜海脊北端隱沒至琉球海溝及耶雅瑪海脊下方之情況、琉球隱沒帶的逆衝斷層、基盤斷層、分支斷層與隱沒滑脫面。第二年則接續第一年成果，分析海底地震儀水平分量資料，建立花東海盆、加瓜海脊、西菲律賓海盆、琉球海溝、耶雅瑪增積岩體、琉球弧前海盆以及琉球島弧之地殼S波速度構造。從臺灣東部海域地殼P波與S波速度構造可探討琉球隱沒帶附近的斷層、岩漿與破裂帶分佈以及其孕震機制。 Horizon velocity analysis and pre-stack depth migration of long-offset reflection data along T4, T5 and T6 conducted by our previous project may provide us better P-wave velocity sedimentary structures across Huatung Basin, Gagua Ridge, West Philippine Basin, Ryukyu Trench, Yaeyama Accretionary Prism, Ryukyu Forearc Basins and Ryukyu Arc. Pre-stack depth migration along T4 shows the faulted structures and the rugged basement in the Huatung Basin that may have resulted from subduction of the Philippine Sea Plate and collision of the Luzon Arc. Near the Taitung Canyon, a basement rise and a low velocity zone of about 3 km/s possibly due to the right-lateral strike-slip fault were found. Across the Ryukyu Trench, sedimentary layers along T5 indicated the accretionary prism and a notch incurred by northward subduction of the Gagua Ridge. High velocity zone (3.7 km/s) in the sedimentary layer near the central T5 may have resulted from subduction of a seamount. In the first year of the project, sedimentary structures imaged from pre-stack depth migration and crustal structures constrained by refracted and reflected travel-times picked from hydrophone and vertical components of OBS data along the same profiles will be integrated to build the P-wave velocity and interfaces of crustal structures. Crustal velocity structures in the Ryukyu subduction zone lead us to investigate the basement depth in the Huatung Basin, West Philippine Basin, Ryukyu Forearc Basins, the northward subduction of the Gagua Ridge beneath the Ryukyu Trench, the thrust faults, the basement faults, spry faults and the decollement in the subduction system. In the second year of the project, horizontal components of OBS data will be analyzed to obtain the S-wave velocity crustal structures across Huatung Basin, Gagua Ridge, West Philippine Basin, Ryukyu Trench, Yaeyama Accretionary Prism, Ryukyu Forearc Basins and Ryukyu Arc. Based on the P-wave and S-wave velocities of the crustal structures off eastern Taiwan, we can understand more about faults, magma, fracture zones and seismogenic zones in the Ryukyu subduction system.

Keyword(s)

加瓜海脊
北呂宋島弧
海底地震儀
琉球隱沒帶
Gagua Ridge
Northern Luzon Arc
Ocean-Bottom Seismometer (OBS)
Ryukyu Subduction Zone

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Crustal Structures of P-Wave and S-Wave Velocity off Taiwan and Philippine Sea Based on OBS Data (III)

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