臺北都會區為一沉積盆地，容納了台灣近四分之一的人口，其西側以山腳斷 層與林口台地為界。山腳斷層為一東傾的正斷層，其斷層面向東延伸至台北都會 區下，具有產生規模6以上地震的可能性。若發生地震事件，沉積盆地內的軟弱 沉積物與複雜的斷層帶構造，會使臺北都會區的地表震動產生明顯的盆地放大效 應，造成巨大的危害。然而，由於山腳斷層被第四紀沉積層覆蓋，缺乏露頭與高 解析的地震資料，其斷層面位置與幾何形貌仍不明確。 本研究利用新興的分布式聲學感測（Distributed Acoustic Sensing， DAS）技 術，將既有的光纖電纜轉化為跨越山腳斷層的超高密度線性陣列，結合環境噪訊 互相關與波束成形分析量測沿線光纖路徑上的雷利波相速度頻散曲線，並以貝氏 蒙地卡羅反演法建立跨斷層帶的高解析度二維剪力波速度模型，測繪山腳斷層帶 與台北盆地的精細構造。 結果顯示，在臺北盆地與林口台地之間存在明顯的速度差異，清楚描繪出盆 地邊界山腳斷層向東傾的幾何形態，以及其斷層面可能的位置。頻譜比分析也顯 示臺北盆地一側具有顯著的場址放大效應，主頻約在2赫茲左右。本研究展示了 利用普遍存在的電信光纖(暗光纖)來探測都會區斷層帶細部構造與地震動放大 效應的潛力，這對於都市地震災害減輕具有重要意義。;The Taipei metropolitan region， home to nearly one quarter of Taiwan’s population， is situated atop a sediment‐filled basin bounded to the west by the active Shanchiao normal fault. Despite its potential to generate earthquakes exceeding magnitude 6， the subsurface geometry and internal architecture of the Shanchiao Fault remain poorly resolved， largely due to the masking effects of Quaternary alluvium and the scarcity of seismic datasets with sufficient spatial resolution. The combination of thick， low‐velocity sediments and the structural complexity of the fault zone exerts strong control on seismic‐wave propagation， leading to pronounced amplification and extended ground-shaking durations within Taipei Basin. Here we deploy Distributed Acoustic Sensing (DAS) on an existing dark fiber cable that crosses the fault， transforming a standard telecommunication conduit into an ultradense seismic array capable of imaging shallow structures at unprecedented detail. By performing ambient noise cross-correlation and array beamforming， we extract Rayleigh-wave phase-velocity dispersion along the cable and invert them for a high-resolution two-dimensional shear-wave velocity model across the basin–fault transition. The resulting velocity structure reveals a sharp contrast between the Taipei Basin and the Linkou Tableland， constraining the east-dipping fault geometry and delineating a probable damage zone. Additional spectral-ratio analyses highlight strong frequency-dependent site amplification within the basin. Together， these findings demonstrate the power of repurposing widely available telecom fiber networks for high-fidelity subsurface imaging and for quantifying near-surface amplification effects critical to seismic hazard mitigation in densely populated urban environments.
