台北是台灣的政治經濟中心，鄰近的山腳正斷層為北台灣最主要的活動構造之一。近年台灣建立起大範圍的全球衛星定位系統(GPS)觀測網，以連續且密集的近斷層地表運動觀測結果，來偵測分析活動斷層的地下形貌及滑移變形。本研究以運動學的角度，先使用前人研究提出的山腳斷層幾何參數，建立其彈性半空間錯位模型，再以北台灣2006 - 2016年間41個GPS連續站及2006 - 2015年間81個移動站之水平速度場，逆推分析山腳斷層的間震滑移速率分布及特性。方法上先以非負最小二乘法計算大範圍斷層面上的平均滑移速率值，再用非負吉洪諾夫正則化方法分析斷層的滑移分布特性及其與地表速度場的關聯，並應用經驗自助抽樣法(empirical bootstrap)估算滑移誤差。結果顯示山腳斷層的間震左滑分量集中在低傾角的深部(>6 km)子斷層，速率約為11.5–24.9 mm/yr；而正滑分量在高傾角(~75º)的淺部子斷層為3.1–8.7 mm/yr，深部子斷層則為5.0–9.3 mm/yr。根據比較觀測及由模型擬合的地表速度場，本文推論山腳斷層的間震滑移除了一般認知由跨斷層的西北—東南伸張所引起的正斷層分量外，其深部低傾角部分的左滑分量主要反映了因區域碰撞及隱沒作用所造成的順時針地殼旋轉，在構造上類似於底部滑脫面的震間變形。本研究以測地資料提供了山腳活斷層的短期滑移速率，可與地質資料所得的長期速率進行結合比較，做為斷層危害及潛勢分析之參考依據。;The Shanchiao active fault is an important seismogenic structure in northern Taiwan, which is adjacent to Taipei— the capital city and administrative and economic center of Taiwan. In recent years, a dense GPS monitoring network has been built up in Taiwan, with a purpose of analyzing the location and deformation near active faults. From the perspective of kinematics, this study adopted some geometric models of the Shanchiao fault from previous studies to establish elastic half-space dislocation models and to evaluate interseismic slip rate of the fault. By utilizing the horizontal velocity field from 41 continuous and 81 campaign GPS stations observed from 2006 to 2015, this study performed non-negative least squares method to obtain average slip rates on four subfaults. Moreover, non-negative Tikhonov regularization method was used to resolve fault-slip distribution, and its relation to the surface velocity field was discussed. An empirical bootstrap method was then applied to estimate the confidence interval of slip rate. Results show that the shallow (<6 km) and steep (~75º) part of the Shanchiao fault slips mostly normal with interseismic rates of 3.1–8.7 mm/yr, consistent with the NW-SE streching found across the fault. The deep and flat part, however, behaves like a low-angle detachment fault for accommodating the proposed regional post-orogenic extension and clockwise rotation, with normal and left-lateral slip rates of 5.0–9.3 mm/yr and 11.5–24.9 mm/yr, respectively. These geodetically implied “short-term” fault-slip rates can be considered as an independent dataset other than the “long-term” geological slip rates, where the two should be integrated for evaluating the potential earthquake hazard of the Shanchiao fault.
