CREATE V:亞洲增生與碰撞大地構造研究總計畫(III)-分析越南西北部奠邊府斷層系統的活動性

2011-08-012024-05-14https://scholars.lib.ntu.edu.tw/handle/123456789/657796摘要：從構造運動的觀點而言，西藏高原的東緣和鄰近區域自晚新生代以來就產生一系列 活動的左移橫移斷層，其中奠邊府斷層(Lai Chau-Dien Bien fault, LCDBF)被視為左移橫移斷層的一支，從靠近越南-中國邊界紅河斷層延伸至越南的Lai Chau 和奠邊省，向南延伸至了寮國的Louang Phrabang 省。其斷層帶長度在越南約為160 公里長，6-10 公 里寬。在新生代以來，奠邊府斷層經歷兩次主要的構造運動，一次主要以右移帶有逆斷層分量的橫移斷層為主，另一次則為左移帶有正斷層的分量的橫移斷層。近年來不 少人利用大地測量研究此區域的鮮水河-小江斷層、紅河斷層和奠邊府斷層的活動性。鮮水河-小江斷層具有12±4 mm/yr 的左移剪切量，但是紅河斷層的活動性則不明顯，每年約 1-2 公厘。至於奠邊府斷層的活動性仍然不清楚。根據地震資料，奠邊府斷層帶及其鄰近區域常有規模大於四的地震產生，且在1935 年和1983 年在奠邊府斷層附近地區也曾發生規模接近7 的災害性地震，因此對於鮮水河-小江斷層、紅河斷層和奠邊府斷層地震潛勢的評估，需要大地測量的方法監測其地表變形。因此本研究嘗試在橫跨奠邊府斷層帶建立6 個連續性GPS 監測站，利用20 個單頻GPS 加密研究區地殼活動性觀測，並整合此地區7 個移動站的觀測鮮水河-小江斷層、紅河斷層鄰近地區連 續性GPS 監測站，並結合C 波段和L 波段的雷達影像，經由永久性散射點合成孔徑 雷達干涉技術(PS-InSAR)。藉此了解鮮水河-小江斷層、紅河斷層和奠邊府斷層帶的活動性和地殼變形特性。根據地表變形資料，我們將利用數式模式反演斷層帶幾何形態和斷層面之滑移率並評估其活動性及地震潛能。初步6 個連續性GPS 分析成果顯示，全球框架ITRF2005 下6 個站的速度向量為28.4-51.1 mm/yr，方位角在91.4 至136.3 度 之間。若以位於奠邊府斷層西側的MTEV 站為參考點，則DBIV 站之速度為8.2±1.1 mm/yr，方位角為018 度，顯示奠邊府斷層具有明顯的左移分量，同時西北-東南向的斷層帶亦顯示右移的橫移或橫移壓縮的變形特徵。 <br> Abstract: From the tectonic point of view, the eastern part of the Tibetan plateau and adjacent areas from the late Cenozoic to present time, the Lai Chau-Dien Bien fault (LC-DBF) is considered as one of the left-lateral strike-slip faults. About 500 km in length, the Lai Chau-Dien Bien fault (LC-DBF) stretches from its nearest point to the Red River fault near Vietnam-China border, through Lai Chau, Dien Bien Provinces in Vietnam, to its end in Louang Phrabang Province in Laos. The fault trace in Vietnam is approximately 160 km long and 6-10 km wide. During the Cenozoic, the LC-DBF passed two main tectonic stages, which are characterized by right-lateral strike-slip movement with reverse component and by left-lateral strike-slip mechanisms with normal component, respectively. Based on geodetic measurements, the activity of the Xianshuihe-Xiaojiang fault system, the Red River fault and the LC-DBF are investigated. The 12±4 mm/yr left-lateral shear was predicted along the Xiansuihe-Xiaojiang fault system. The 1 or 2 mm/yr was reported along the Red River fault. However the activity of LC-DBF is not well understood. Based on the seismic data, some earthquakes with magnitudes larger than 4.0 often occurs along the fault zone and its adjacent area. Thus the seismic hazards assessment are crucial in this area, thus we propose to establish a local network with several continuous GPS (CGPS) stations across the LC-DBF zone in the Northwest of Vietnam to detect the fault activity and the deformation pattern. This CGPS network could be integrated with seven campaign mode GPS stations and the CGPS networks across the Xianshuihe-Xiaojiang fault system. We also try to use the PS-InSAR technique to detect the surface deformation in study area by using c-band and L-band radar images. Furthermore, a numerical model will be carried out to well characterize the deformation pattern and slip rate along the fault patches of Xianshuihe-Xiaojiang fault, Red River fault and LC-DBF systems. The preliminary results of 6 continuous GPS in northwestern Vietnam show that the station velocities are in the range of 28.4-51.1 mm/yr with the azimuth of 91-136 in the framework of ITRF2005. The velocity of 8.2±1.1 mm/yr in a direction of 018 is observed at station DBIV indicate that a significant left-lateral shear occurs along the Lai Chau-Dien Bien fault. In addition, the right-lateral strike-slip and transpressional deformation are observed in the NW-SE trending fault zone in NW Vietnam.奠邊府斷層永久性散射點合成孔徑Lai Chau-Dien Bien faultLCDBFPS-InSARCREATE V:亞洲增生與碰撞大地構造研究總計畫(III)-分析越南西北部奠邊府斷層系統的活動性