摘要
本研究搜集1995-2005年內政部一、二等衛星控制點，共127個觀測站資料來探討台灣北部地區構造活動之機制。由於台灣北部地區之地殼變形受到於2002年3月31日規模6.8花蓮外海地震的影響（Chen et al., 2004），因此本研究藉由時間序列的分析並修正2002年花蓮外海地震之同震位移，來估算各測站相對於穩定大陸邊緣（澎湖白沙站，S01R）之速度場，並利用速度場推求台灣北部地區之應變速率、剪應變率、旋轉率。經由短時期的GPS重複觀測來探討台灣北部地區的地殼變形行為，期望能對以下的問題做進一步之討論：塊體旋轉是如何在台灣東北部與弧後張裂產生相互關係？是否能顯示與古地磁研究一致的特性？弧陸碰撞的應力是否有傳遞到台灣北部地區？研究結果顯示，整個台灣北部地區GPS速度變化以宜蘭平原最為顯著，相對澎湖（S01R）之最大相對速度為41.2 mm/yr，新竹、桃園一帶，速度平均值約在4.62 ± 2.86 mm/yr，平均方位角在315°大致都往西北方向，在台北地區以金山-山腳斷層系統為分界，於斷層西側速度向量皆往西北方移動，而斷層之東側則由東北方順時針往東南方移動，此區之平均速度約2－3 mm/yr。應變率最大的區域主要集中在東南方之宜蘭平原沿海一帶，介於0.50－1.98 μstrain/yr，其他的區域皆小於0.50 μstrain/yr以下。在地殼變形上，由於菲律賓海板塊由西北方向不斷往前擠壓而又受到位於台灣西北端海域觀音基盤高區之阻擋，使得此新竹、桃園地區之變形型態呈現西北-東南壓縮。在了北北西海域由於不在受到觀音基盤高區阻擋，介於南崁斷層與金山-山腳斷層系統之間，變形型態逐漸轉為近乎東-西方向以及東北東-西南西伸張。而金山-山腳斷層系統之右側，受到物質側向伸張及弧後伸張之作用力影響變形型態呈現近乎東-西向伸張且伴隨著由北順時針向東南旋轉。由於山脈抬升造成物質平行山脈走向的流動加上沖繩海槽向西北-東南伸張，使得宜蘭平原的速度變化由北順時針往東南旋轉且愈往南速度愈大，由此我們推論沖繩海槽為不對稱之弧後張裂。

Abstract
We use 11 years (1995~2005) 127 stations from a densely-spaced Ministry of Interior GPS network to investigate the tectonic mechanisms of northern Taiwan. Crustal defomation of northern Taiwan is affected by the 2002 Mw 6.8, Hualien offshore earthquake, therefore, we began from time series analysis and corrected for co-seismic displacement of Hualien offshore earthquake to evaluate the velocity field related to a stable continental margin station, S01R. From velocity field analysis, we further discuss the strain rate, shear strain rate and rotation rate. Moreover, we will discuss the following questions especially expect to discuss: (1) What’s the relationship between block rotation and back-arc extension of noth-eastern Taiwan? (2) Is the observation coherent with paleomagnetic evidences? (3) Does the collision stress indeed propagate to northern Taiwan? Our results show that the velocity field varies largely in Iian plain, where the maximum velocity is 41.2 mm/yr; Huinchu and Taoyuan area is 4.62 ±2.86 mm/yr in average, and the orientation are about north-west (315º). In Taipei area, an apparent boundary was located in Chinshan-Shanchiao fault system; the velocity field are toward north-west in the western-flank, and the eastern flank presents a clockwise rotation pattern from north-east to south-east with average velocity 2~3 mm/yr in rough. The area with maximum strain rate is along coastal Ilan plain (0.5~1.98μstrain/yr), and the other areas are less than 0.5μstrain/yr. In northern Taiwan, due to the continuous north-west collision from Philippine Sea plate and the obstruction of Kuanyin High, the deformation of Huinchu and Taoyuan area is compression toward NW-SE. Nankan fault and Chinshan-Shanchiao fault system defom as NS and ENE-WSW tensile for the sake of lacking the resistance of Kuanyin High. The deformation of east side of Chinshan-Shanchiao fault system reveals EW tensile and clockwise rotation from north to south-east due to lateral extrusion and back-arc extension mechanism. The whole velocity field pattern of Ilan plain appears clockwise rotation and velocity increases southward. Therefore, the Okinawa trough appears to be an asymmetry extension.

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