臺灣南部外海為馬尼拉-呂宋隱沒系統，地震頻繁，地震時若誘發海底山崩，可能引發海底濁流。研究海床濁流沉積物，可協助判斷隱沒帶發生大地震的時間與可能的週期。本研究利用墾丁盆地及高屏峽谷下游共七站岩心，對沉積物做物理參數、化學參數、有孔蟲定年等分析，研究大地震發震週期。 分析結果顯示，位於增積岩體上部斜坡的墾丁盆地，近一萬年來紀錄六次較大規模的濁流事件。接近高屏峽谷的下部斜坡區域，事件層層數至少多出一倍以上。推測高屏峽谷流域的事件層較多、厚度較薄，為強降雨事件所造成的異重流溢堤後堆積於此處，然其中亦包含地震所造成的濁流堆積事件。而位於獨立盆地中的岩心，因不受峽谷系統影響，不但濁流發生的頻率相對較少、事件層厚度較厚，再加上以有孔蟲伴隨砂質沉積物堆積為主，研判其主要的形成機制為由地震觸發海底山崩所造成的濁流沉積物。 利用濁流層下方的半遠洋沉積物進行定年，發現墾丁盆地中最近一次的事件約發生在距今400年內，參照歷史文獻後，最有可能為1781年屏東港西所發生的地震海嘯事件，透過地層層序及沉積特徵對比，顯示此事件於分歧斷層下盤的岩心也有記錄。 墾丁盆地的濁流層常成雙出現，即兩次濁流間隔時間短，經過數千年長期穩定後，又出現兩次濁流事件的週期。本研究的岩心記錄的6,500年內僅發現四個週期，相較於世界上隱沒帶平均約每數百年至一千年發生一次巨大地震的頻率還來得小，推測本研究的岩心可能沒有完整記錄馬尼拉隱沒帶的強震史；或是馬尼拉隱沒帶的板塊邊界斷層的強震週期，較世界平均值長很多，暗示此區板塊耦合較弱。;The offshore area of southern Taiwan is the Manila subduction system prone for large earthquakes. Earthquake-triggered submarine landslides and ensuing turbidity currents are likely to deposit mass transport deposits and turbidites in the intra-slope basins across the accretionary wedge. Studying turbidites may therefore determine the timings and recurrence intervals for subduction zone large earthquakes. Seven cores from the perched Kenting Basin in the upper accretionary wedge as well as the intra-slope basins in the overbanking area of the lower Gaoping Canyon are used to characterize sedimentary facies by using physical and chemical properties of sediments. Carbon 14 dating is performed on forams to constrain sediment ages. The isolated and closed Kenting Basin is free from Taiwan sediment inputs and the most likely source of turbidity currents are submarine landslides presumably triggered by earthquakes. The turbidites are rich in sands and reworked forams, showing typical Bouma sequence. Our analysis shows that there are six episodes of turbidite layers in the Kenting Basin for the last 10,000 years. Some episodes are characterized by two closely spaced turbidite layers. This indicates that the turbidite recurrence interval is around 1,500-2,000 years and some events are characterized by two consecutive turbidity currents separated by a few to tens of years. The most recent event in the Kenting Basin is around 400 years ago, probably corresponding the historical 1781 tsunami event in SW Taiwan. However, in the overbanking area and close to the river-connected Gaoping Canyon, the event beds are, at least, doubled in number. Turbidity currents in this area can be driven by earthquake-triggered submarine landslides as well as climate-driven density flows, such as hyperpycnal turbidity currents related to onshore floods in the Gaoping River. We suggest that a lot more turbidites in this area are due largely to hyperpycnal flows as evidenced from reported recent hyperpycnal events along the Gaoping Canyon.
