南台灣恆春區域新期構造運動之研究

Neotectonics of Hengchun Area, Southern Taiwan

李珀儂(Po-Nong Li)

指導教授 ： 陳于高

國立臺灣大學/理學院/地質科學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00190

摘要

本研究區域位於台灣南端，包含陸上之恆春半島與一部份海裡之恆春海脊。鑒於本研究區域過往之前人研究，鮮少同時討論對陸上與海中之地質、地形與構造之關係。本研究冀望藉由地理資訊系統(GIS)、數值地型模型、航空照片、野外調查、反射震測資料與多音束測深系統(MBS)等工具，對於本研究區域之地形進行重新檢視，進而判斷近期活動構造之運動行為，最後整合各項資訊，對恆春區域之新期構造運動作整體性之了解。
陸上之調查結果將恆春半島上之海階地形面由老至年輕劃分為一到八期，整體恆春半島皆有第八期之海階分布，表示恆春半島近期來處於一個整體隆升之構造階段。西恆春台地上由五至七期之海階分布，愈老之海階紀錄愈多地形東傾之行為，表示西恆春台地近期來一直處於構造傾動之階段。鵝鑾鼻半島上由一到六期之海階分布，海階之變形顯示鵝鸞鼻半島整體為一背斜構造。恆春斷層沿線之構造地形，呈現恆春斷層為一左移走向分量大於逆衝分量之斷層，並在湖內以南，分為三條分支斷層，應該與恆春斷層之走向於湖內發生轉折有關。
海中之地形顯示恆春區域大體上可視為一背斜構造，其主要特徵為背斜之頂部寬廣，兩翼呈現陡峭之地形，本研究稱此一背斜為恆春背斜。恆春背斜乃由東邊的南縱海槽斷層，與西邊的西恆春斷層所組成之一上衝構造所造成。其中由震測剖面之解釋並配合海底地形的分析，可以得知西恆春台地因為座落於西恆春背斜之東翼，而造成其地形上東傾與海階面變形之結果。另外由震測與地形資料之分析，發現恆春斷層出海後，走向轉為北偏西30度，便一路往南延伸與南縱海槽斷層相接。海深資料顯示本研究區分布有眾多之正斷層，多為因應大地應力而生。
整合上述之種種資料，本研究區域之新期構造運動以南縱海槽斷層與西恆春斷層所組成之上衝構造為主，其中恆春斷層以左移之運動方式斜切而過。

關鍵字

恆春半島 ； 恆春斷層 ； 西恆春斷層 ； 西恆春背斜 ； 西恆春台地 ； 上衝構造

並列摘要

The study area including onshore Hengchun Peninsula and part of offshore Hengchun Ridge is located at southern Taiwan and called Hengchun Area. Because the previous studies about Hengchun Area rarely tie the onshore and offshore geological, geomorphological and structural information together to have a further discussion. This study would like to re-examine the geomorphology of Hengchun Area by using tools such as Geographic Information System (GIS), Digital Elevation Model (DEM), aerial photos, reflection seismic data, and Multibeam Echo Sounding System (MBS). By compiling all the information that we acquire from both this study and previous studies, this study feels like achieving the objective of comprehension of the neotectonics of Hengchun Area.
Marine terraces is divided into eight stages on Hengchun Peninsula, from marine1 (oldest) to marine 8 (youngest). Holocene terraces, marine 8, are widely distributed over Hengchun Peninsula, indicating recently tectonic uplifting of Hengchun Peninsula. On the east-tilting Western Hengchun Tableland, there are marine 5 to marine 7 covering on the surface. The phenomenon of older terraces showing greater slope elucidates the continuously tilting of Western Hengchun Tableland. The deformation of marine terraces on Oluanpi Peninsula shows that the Oluanpi Peninsula itself is an antiform structure. The tectonic-related landforms along Hengchun Fault trace indicate that the left-lateral slip of Hengchun Fault is greater than dip slip and the Hengchun Fault separates into three branchces south of Hunei as the result of fault-strike change.
Offshore bathymetric data shows that Hengchun Area is a huge antiform shape with broad top and steep limbs. This antiform is called Hengchun Antiform and is made up by a pop-up structure. The pop-up structure is composed of South Longitudinal Trough Fault to the east limb and Western Hengchun Fault to the west limb. Based on interpretations from seismic and bathymetry data, this study relates the east-tilting and deformation of marine terraces on Western Hengchun Tableland to the fact that Western Hengchun Tableland itself is the east limb of Western Hengchun Antiform. The strike of Hengchun Fault turns to N30oW when it extends southward offshore and then connects with South Longitudinal Trough Fault. The pervasive normal faulting in Hengchun Area is probably in response to regional tectonic stress.
In summary, nectectonics of Hengchun Area is characterized by a pop-up structure and Hengchun Fault which obliquely cuts through the Hengchun Area with larger sinistral displacement than vertical displacement.

並列關鍵字

Hengchun Fault ； Hengchun Peninsula ； Western Hengchun Tableland ； Western Hengchun Fault ； Western Hengchun Antiform ； Pop-up structure

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