鳳山轉換斷層現今之斷層活動行為及其地震潛能分析

Fault Behavior Analysis of the Fengshan Transfer Fault and Its Earthquake Potential Assessment

藉由台灣西南部之地形特徵解析與歷年GPS觀測資料分析顯示，鳳山轉換斷層極可能為台灣西南部主要活動斷層之一。然而，目前對於鳳山轉換斷層的地表變形形態及其地震潛能所知甚少，故本研究利用台灣西南部2002至2010年共205個GPS測站資料，分析鳳山轉換斷層的斷層活動行為及其地震潛能。本研究首先以Bernese軟體解算GPS資料來獲得各測站之每日坐標時間序列，並採用最小二乘法計算相對於澎湖之水平速度場。水平速度場分析結果指出，旗山斷層以西約為10-30mm/yr，以東則約為50mm/yr。速度方位角除了在跨鳳山轉換斷層以西之沿海區域約為245°外，其他區域則約為268°。跨越鳳山轉換斷層之速度剖面顯示，跨斷層的平行斷層走向分量皆約為15mm/yr。而垂直斷層走向分量於斷層北段有約1.9mm/yr之擠壓速率，中段有約1mm/yr之伸張速率，南段則有約5.2mm/yr之伸張速率。亦即，鳳山轉換斷層為一條以左移為主之走向滑移斷層，斷層北段為具有擠壓分量之鎖定斷層，斷層中段以及南段則為具有伸張分量之潛移斷層。二維斷層模型之結果顯示，斷層傾角約為50°，深度則約為7至13公里。斷層北段之最大震間滑移速率約為17.0mm/yr，斷層中段約為25.8mm/yr，而斷層南段則約為36.0mm/yr。最後藉由斷層模型進一步估計斷層帶之能量累積約為2.15×1024 dyne-cm/yr，且預估之地震週期約為117年。 The analysis of GPS measurements around the Fengshan transfer fault(FTFZ) indicates that the FTFZ may be a major active fault in SW Taiwan. However, the fault geometry, the deformation pattern, and the earthquake potential of the FTFZ still remain unclear. Therefore the observations of 205 GPS stations from 2002 to 2010 are used to understand the deformation pattern in SW Taiwan. The pattern of the horizontal velocity field shows a significant velocity gradient from 30 mm/yr to 10 mm/yr west of the Chishan fault, whereas velocities are about 50 mm/yr in 268° east of the Chishan fault. For the area west of the FTFZ, the velocity azimuth changes into 245°. The horizontal velocity profile shows that the fault parallel component has about 15 mm/yr difference across the fault, indicating a sinistral strike-slip fault. Across the northern segment of the fault, it shows an about 1.9 mm/yr shorteningrate, while about 1.0 mm/yr and 5.2 mm/yr extension rates are across the central and southern segments, respectively. Therefore the FTFZ is a left-lateral fault and the northern segment is locked with contraction, while the central and southern segments are creeping with extension. The fault geometry of the FTFZ inferred by 2D fault model shows the dip is ~50° and the depth is about 7 to 13 km. The maximum interseismic slip rates are~17.0 mm/yr, ~25.8 mm/yr, and ~36.0 mm/yr for the northern, central, and southern segments, respectively. Based on the modeling result, the estimated energy accumulation rate is 2.15 × 1024 dyne-cm/yrand the recurrence interval of the earthquake is about 117 years.

The analysis of GPS measurements around the Fengshan transfer fault(FTFZ) indicates that the FTFZ may be a major active fault in SW Taiwan. However, the fault geometry, the deformation pattern, and the earthquake potential of the FTFZ still remain unclear. Therefore the observations of 205 GPS stations from 2002 to 2010 are used to understand the deformation pattern in SW Taiwan. The pattern of the horizontal velocity field shows a significant velocity gradient from 30 mm/yr to 10 mm/yr west of the Chishan fault, whereas velocities are about 50 mm/yr in 268° east of the Chishan fault. For the area west of the FTFZ, the velocity azimuth changes into 245°. The horizontal velocity profile shows that the fault parallel component has about 15 mm/yr difference across the fault, indicating a sinistral strike-slip fault. Across the northern segment of the fault, it shows an about 1.9 mm/yr shorteningrate, while about 1.0 mm/yr and 5.2 mm/yr extension rates are across the central and southern segments, respectively. Therefore the FTFZ is a left-lateral fault and the northern segment is locked with contraction, while the central and southern segments are creeping with extension. The fault geometry of the FTFZ inferred by 2D fault model shows the dip is ~50° and the depth is about 7 to 13 km. The maximum interseismic slip rates are~17.0 mm/yr, ~25.8 mm/yr, and ~36.0 mm/yr for the northern, central, and southern segments, respectively. Based on the modeling result, the estimated energy accumulation rate is 2.15 × 1024 dyne-cm/yrand the recurrence interval of the earthquake is about 117 years.