屏東平原位於菲律賓海板塊與歐亞板塊交彙的活躍邊界處，是台灣因自然因素和人類影響而引起的土地變形最活躍的地區之一。本研究提出了一個新穎的概念模型，以量化分別由地下水開發和板塊構造所引起的地層下陷量。全球定位系統（GPS）的資料呈現垂向位移的總下陷量，磁環分層式地層下陷監測井（MLCW）則能夠測量從地表到200公尺深度不同位置的垂直變形。本研究採用佳冬與枋寮MLCW地層下陷觀測資料，以及與其鄰近的CLON和FALI GPS觀測站資料，進行深層地層壓縮分析。根據MLCW 2007至2016年的觀測資料，佳冬地區的主要壓縮深度位於距地表104公尺內；枋寮地區的主要壓縮帶則在深度101-156公尺範圍內，與當地用水型態有關。此外，GPS站的垂向位移大於MLCW的垂向位移量，顯示在200公尺的深度之下仍有額外的垂向變形量。根據本研究分析，此變形並非主要導因於地下水抽取和自然壓密行為，而可能與台灣造山帶的構造釋壓和構造擠壓等板塊構造活動有關，其垂向變形速度約0.9至-4.6毫米/年。因此，本研究成功地分離了由於地下水開發和構造活動引起的地層下陷量，研究結果可提供地下水資源管理與屏東平原構造物理研究的參考。;Pingtung coastal plain, located at the active convergent boundary between Philippine Sea plate and Eurasian plate, is one of the most active areas regarding land deformation induced by both natural issues and human impact in Taiwan. This study proposed a novel conceptual model in order to quantify land subsidence caused by groundwater extraction and plate tectonics, respectively. The data of the Global Positioning System (GPS) stations are used to illustrate the total subsidence concerning vertical displacement. A system called multi-layer compaction monitoring well (MLCW) is able to measure the vertical deformation in different depths from the earth′s surface to the depth of 200 m. There are two GPS stations named CLON and FALI, which are set close to the MLCWs and located in Jiadong and Fangliao areas, respectively. According to MLCW survey data from 2007 to 2016, the major compaction zone is within 104 meters from Earth′s surface in the Jiadong area. In Fangliao area, the major compaction zone is in the range of 101-156 m of the soil stratigraphy. Moreover, the vertical displacement of GPS stations is larger than that of MLCW, which indicates that there exists additional vertical deformation beyond the depth of 200 m. From the analyses, this deformation should not be due to groundwater extraction and natural compaction. The phenomenon could be due to the plate tectonic activities associated with tectonic escape and tectonic extrusion of the Taiwan orogeny. The vertical deformation rate ranges from 0.9 to -4.6 mm/year. Subsidence due to groundwater extraction and tectonic activity is thus successfully separated. So, this idea is not only a key issue for groundwater management but also for tectonophysical studies in Pingtung plain, Taiwan.
