新竹地區活動斷層特性研究

Abstract

新竹地區為台灣高科技重鎮，人口密集、產業林立，為有效預防及降低天然災害，調查本區的活動斷層，有著迫切之必要性。本研究利用新竹平原地區由中央地質調查所提供的鑽井岩芯，進行岩相分析與地層對比，建立地質剖面配合碳十四定年探討新竹區域的長期地殼變動速率，同時配合數值模型地形圖 (DTM) 進行階地對比與野外調查瞭解新竹斷層於近地表的構造變形型態；最後，由長期垂直滑移速率、短期地殼水平變動速率與短期地殼垂直變動速率配和地下構造討論新城斷層、新竹斷層與湖口斷層的構造模式。由海相沉積物求得的地殼變動速率在斷層兩側的差值顯示新竹斷層平均長期垂直錯移速率為1.0 ±2.4 mm/yr、而湖口斷層為0.3±3.0 mm/yr。另根據螢光定年及頭前溪南岸各時期階地的錯距，新城斷層晚更新世以來的平均長期垂直錯移速率為1.1±0.3 mm/yr。

In order to prevent and reduce the geo-hazard damages caused by earthquakes in the high-tech center in Hsinchu area, it is necessary to study the behavior and activity of active faults in the area, including the Hsincheng Fault, Hsinchu Fault and Hukou Fault from south to north. Major tectonic geomorphological features were mapped using 5m resolution digital terrain models (DTM) and were checked in the field. 57 bole-holes provided by Central Geological Survey are re-analyzed in order to decide the location position of the faults in areas where the fault traces are ambiguous or covered by thick Holocene deposits. For estimating long-term crustal vertical deformation rates, boleholes containing Holocene marine deposits are analyzed and C14 dating samples are collected as much as possible. Combining the dating results with the eustatic water depth, sample depth and paleo-environmental water depth, the long-term crustal vertical deformation rates since the last glacial maximum (LGM, 18 ka) can be calculated. Long-term vertical offset rate of the Hsinchu fault is 1.0 ±2.4 mm/yr, and long-term vertical offset rate of the Hukou Fault is 0.3±3.0 mm/yr. From the ages and offsets of river terraces, the long-term average vertical offset rate of the Hsincheng fault can be calculated to be 1.1±0.3 mm/yr.