利用淺層反射震測法探討公荖坪斷層

Abstract

九二一大地震之後，車籠埔斷層及其相關構造引起學界熱烈的討論。本文探討豐原附近之公荖坪階地內的公荖坪斷層，該斷層鄰近車籠埔斷層北段轉彎處及地表破裂達九公尺的位置。過去的研究曾以航照判釋與野外調查指出該階地內有一明顯的斷層小崖，並推測公荖坪段層存在，且為車籠埔斷層的副斷層，但其地下構造卻始終從未被偵測。本研究以地形資料及淺層反射震測法 ，仔細檢查公荖坪斷層及其週遭的地下構造形貌，結果證實該斷層確實存在，並推測其可能的形成機制是受車籠埔斷層向西及向北逆衝而上時所伴生的副斷層；同時亦受到北側TT-boundary之障礙阻擋，以致上盤地層因錯動擠壓而撓曲變形，甚至衍生一條小規模的背衝逆斷層與部分的地層陷落。

After the 1999 Chi-Chi earthquake, the Chelungpu fault and its related structures have attracted much attention of researches. This paper discussed a fault on the Gonlauping terrace, which is close to the particular position of the Chelungpu fault where an abnormally large rupture (~9 m) occurred during the earthquake. Previous geographic and geologic studies have confirmed the existence of the Gonlauping fault, however, its underground feature has never been detected. This study used the aerial photograph annotating and the shallow reflection seismic method to examine the fault. The structure surrounding the fault has been carefully mapped to reveal its role in the structures of the major Chelungpu fault. The Gonlauping fault, though not long, was proved to be a significant fault. Keywords reflection seismic method, river terrace, Gonlauping fault.