池上斷層的古地震研究

Paleoseismology of the Chihshang Fault

朱曜國(Yao-Kuo Chu)

指導教授 ： 陳文山

國立臺灣大學/理學院/地質科學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02908

摘要

花東縱谷為板塊邊界，縱谷中斷層活動活躍並伴隨頻繁地震。位於縱谷南段的池上斷層，其斷層崖線明顯，且近十幾年來的研究顯示斷層的變動速率相當高。
此外，縱谷內最近規模較大的兩次地震(1951年台東地震地震與2003年成功地震)的成因都與池上斷層有關。本研究將針對池上斷層進行古地震調查。
基於前人研究與實際野外調查，選定富里-萬安做為研究區域。於區域南段的大坡、錦園、萬安3處場址進行槽溝開挖，並以5口鑽井岩芯(RH01-05)及區域河階調查加以輔助。藉此探討池上斷層的古地震事件次數、週期及長期抬升速率。
經由槽溝開挖調查及鑽井岩芯資料的輔助，顯示池上斷層為朝東傾的高角度逆斷層，斷層傾角為45°以上。槽溝紀錄中並無法確切了解池上斷層的古地震次數，僅可知800年來至少有5-10次以上的古地震事件，而地震週期(T)為50年≦T<170年。
區域內北、中、南階地的抬升速率分別為23.5-27mm/yr、27.4-46.3mm/yr與20.9-26mm/yr。而錦園2號槽溝與鄰近南方階地對比所得的抬升速率為21.2-26 mm/yr。池上斷層的長期抬升速率約為26-27.4mm/yr。此外，池上斷層間震時期潛移造成的垂直變形量遠大於同震的垂直變形量。因此，池上斷層的活動以潛變變形為主，同震變形為輔，其活動模式為高潛變位移低同震位移模式。
由槽溝剖面與鑽井對比可發現，在斷層西側有著分支斷層。在地形上，區域的南北兩方，斷層西側仍有隆起階地存在，顯示斷層西側有著構造存在，此構造可能為分支斷層。而藉由南北兩方階地與中央階地的抬升速率對比可發現，中央階地抬升速率大於南北兩方階地的抬升速率。此速率差異應為分支斷層存在所造成之影響。因此，部份池上斷層存在有分支斷層。分支斷層位於區域的南北兩方。

關鍵字

池上斷層 ； 古地震 ； 地震週期 ； 長期抬升速率

並列摘要

The Longitudinal Valley is an active plate boundary between the Eurasian and Philippine Sea plates. The Chihshang fault located in the southern part of the Longitudinal Valley is an active thrust fault. During the past 50 years, two large earthquakes of the 1951 Taitung earthquake(Mw 6.3) and the 2003 Chengkung earthquake (Mw 6.8) occurred along the Chihshang fault.
The study is aimed at the paleoseismology of the Chihshang fault for understanding the paleoearthquake events, recurrence time, and long-term slip rate. We selected three trenched sites in the Tapo, Chinyuan, and Waan areas and had five cored boreholes along the fault. Additionally, we also surveyed the river terraces on the hanging wall of the fault.
Based on the trench investigation and well-logging record, it shows that the dip of the Chihshang fault is about 45°. Through the paleoseismology study on the Chinyuan and Waan sites, it can be identified at least 5-10 paleoearthquake events for the past about 800 years, and estimating that the Chihshang fault has produced large earthquake with a recurrence interval of 50-170 years. The long-term slip rate is 26-27.4mm/yr based on the uplifted river terrace on both sides of the fault.
Based on the well-logging data, trench and the topographic investigations, we conjectured that some branch faults lie to the west of the Chihshang fault. That branch faults are located in the northern and southern parts of the study area.

並列關鍵字

the Chihshang fault ； Paleoseismology ； recurrence time ； longterm slip rate

參考文獻

楊貴三（1986）台灣活斷層的地形學研究—特論活斷層與地形面的關係。私立中國文化大學地學研究所博士論文，共178頁。

Shyu, J. Bruce H. (2006) A neotectonic model of Taiwan, with a focus on the Longitudinal Vally suture: Ph. D thesis of division of geological and planetary sciences, Caltech, USA, 289P.P.

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