隱沒帶依照沉積物供應量，可粗分為沉積物較多的增積型（accretion type）隱沒帶及幾無沉積物分布隱沒的侵蝕型（erosion type）隱沒帶，侵蝕型隱沒帶由於缺乏富含流體的沉積物隱沒，常導致隱沒岩石圈與上覆岩石圈地殼直接刮擦而崩塌，甚而這些侵蝕下來的塊體部分會跟著隱沒岩石圈隱沒下去。而增積型隱沒帶隱沒沉積物（under-thrusting sediments）的物理性質，包括空隙率、含水量、膠結狀態（consolidation state）及引伸出的隱沒沉積物孔隙液壓及有效應力等參數，深深影響周邊逆衝斷層的活動，進而發生災害性大地震。最新研究顯示，在加拿大外海的卡斯卡迪亞（Cascadia）隱沒帶亦為增積型隱沒帶，根據地震及相關地球物理觀測建議的強耦合地帶，可以觀察到該區隱沒沉積物的膠結呈現過度膠結狀態（over consolidation），經推算之地層孔隙液壓過高，可能導致大地震的發生。反之，在富含天然氣水合物區域，則可以觀察到隱沒沉積物呈現膠結不足的狀態（under consolidation），該區域可能較不容易發生大地震，因此吾人可利用上述方式估算弧前區域的板塊耦合狀態（coupling）。台灣與菲律賓間的馬尼拉海溝、菲律賓海溝至北的琉球海溝亦為增積型隱沒帶，這些海溝在美國地質調查所評估皆可能發生災害性地震，因此極有必要以三年時間針對這些海溝的弧前增積岩體區域，以海洋震測探勘方式取得高解析度的地層速度構造，以估算隱沒沉積物物理性質，進而評估地層的孔隙液壓狀態，以供地震災害分析之用。 ;The subduction zones can be classified as two categories: accretion type and erosive type based on sediments supply. Due to lack of sediments subduction, the subduction crust can be “scratched” overlying crust and result in crustal blocks erosion. Those debris or crustal blocks are even under-thrusted between accretionary prism. In contrast to erosive type margin, physical properties of under-thrusting sediments which include porosity, consolidation status as well as pore pressure and effective stress can affect the activities of surrounding thrust faults. The resent study in the Cascadia margin offshore Canada shows that an over consolidation under-thrusting sediments is identified and suggests a strong coupling origin strongly based on earthquake studies. In the other hand, an under consolidation under-thrusting sediments regime located offshore Orogen State USA is associated with gas hydate distribution on top of high fluid content under-thrusting sediments layer. This indicates that Orogen State region belongs to weak coupling area. Thus, we could take advantage of data processing and analysis methods such as pre-stack depth migration and physical properties calculation from the studies mentioned above and apply them to subduction zones between Taiwan and Philippines. We are going to apply a three year project funds to acquire multi-channel seismic data across fore-arc region of Manila trench and Philippe trench. The results will be expected as very significance whatever on world wide fore-arc region sediment physical properties in subduction zone or social impact on Taiwan and Philippe.
