蘭陽平原位於臺灣東北部，鄰近南沖繩海槽的西南方，脊梁山脈以及雪山山脈分別矗立於盆地南北兩側。蘭陽平原鄰近南沖繩海槽的西南方，根據其主要的地體構造位置、幾何形貌以及其它地球物理的觀察分析，一般認為此處的地殼變形主要是受到沖繩海槽南北伸張應力所造成的影響，由於菲律賓海板塊持續向歐亞大陸板塊碰撞及隱沒，長期累積能量釋放後的結果，反應在蘭陽平原區頻繁的地震活動上，而這些地震行為也多半與沖繩海槽的張裂性活動有關。由於蘭陽平原地表主要被蘭陽溪所形成之大量沖積物所覆蓋，因此這些可能存在之潛在的活斷層，不容易留下清楚的地形特徵。因此，本研究欲探討蘭陽平原現今地表變形與區域構造之關聯。本研究利用2004年3月至2008年6月期間的EVISAT衛星雷達影像，應用永久散射體差分干涉法分析蘭陽平原之地表變形，本研究結果顯示宜蘭與羅東兩個市中心有明顯的下陷趨勢，而在脊梁山脈與雪山山脈區域呈現地表變形速率抬升的情形。本研究統整現有的地形、地質以及地球物理等資料，例如地震活動等，根據PSI結果顯示最大沉陷區域位於平原的南部，下陷量達每年18公厘，此外，藉由地震斷層模擬模型分析，位於濁水斷層與三星斷層之間存在一個明顯的下陷趨勢，對應到地震最活躍的地區，濁水斷層可能是梨山斷層往北延伸至平原內的界線斷層，而三星斷層可能代表目前存在平原內部的活動斷層，本研究主要結果顯示目前以平原南部為主要構造活動的區域，而此構造活動機制可能並非單純受到沖繩海槽張裂所造成，而是綜合其他地體構造應力所造成，特別是板塊斜向碰撞、火成岩入侵或造山帶邊緣之橫向逃脫，使得蘭陽平原南部的構造活動特性更加複雜。;The Ilan Plain in the northeastern Taiwan is generated by the southwestward extension of the Okinawa Trough and surrounded by the high mountains of the Hsuehshan Range to the north-west, and the Central Range to the south-east. Its eastern coast faces the western tip of the Okinawa Trough, the back-arc basin of the Ryukyu subduction zone. This plain is filled by alluvial materials and is almost equilateral triangular in shape and moderately tilted to the east. Different opinions about the formation of this region and its relationship to the Okinawa Trough have been proposed in the last few decades. In this study, we analyzed the present-day surface deformation of the Ilan Plain and tried to find the relationship with the regional tectonics. Our approach is mainly based on consideration of displacement revealed by Persistent Scatterers InSAR (PSI), totally 23 Envisat images acquired by ESA and observed temporally–variable processes of Ilan Plain between 2004 to 2008 have been used. Our results show a relative subsidence in Ilan and Loudung city, and a slight uplift in the Hsuehshan and Backbone Ranges. When combined with previous geodetic measurements and existing geophysical data, such as seismic activity, our PSI-derived rates of surface displacement indicate that there is convincing subsidence area, located in the southern part of Ilan Plain and characterized by a rate of about 18 mm/yr. In our seismotectonic model, the Choshui Fault is related the opening of the Ilan Basin and presently borders the area of active subsidence associated with the opening of the Okinawa Trough. Our PSI results show that the subsidence occurred in the south of the Ilan Plain. It implies that the opening of the Ilan Plain may have a differing mechanism compared to the Okinawa Trough.
