觀察南部中央山脈自中央氣象局1991年1月~2003年5月之地震資料，可發現數群明顯的地震帶於此發生，且在集集大地震前後地震活動性有明顯不同的分佈趨勢。由中研院所提供的震源機制解（Broadband Array in Taiwan for Seismology，BATS），顯示南部中央山脈發生了一系列以伸張為主的正斷層，而在一個以碰撞擠壓為主的造山帶是如何發育這些正斷層呢？本研究擬利用震源之重新定位，求取震源機制解及區域應力反演來分析南部中央山脈底下的構造機制。
經由三維重新定位後，發現在集集大地震前後，本研究區域下的地震活動性有明顯地不同，且具有數個線性特徵明顯的地震群集。在集集地震前，地震分佈大致呈現近南北向及西北東南向;集集地震過後，地震分佈的走向則轉為西北東南向及近東西向，而整個區域發震的位置亦因集集地震前後有所不同。我們發現那些線性特徵明顯的地震群集幾乎由主餘震序列所構成，在此本研究使用了雙重差分定位法去對這些主餘震序列重新定位，我們看到在中央山脈核心（研究區域東側）底下有一系列地震呈現垂直分佈，而在中央山脈西翼（研究區域西側）則為較水平的地震所分佈。本研究區域之震源機制解幾乎皆為正斷層及走向滑移斷層所組成，僅夾雜少數的逆斷層。斷層面之走向大致為近南北向或西北東南向，其方向性與地震線性分佈相當一致，經由應力反演後也可以清楚地看到本區域呈現東北西南向的伸張，相信是大地應力所造成的結果。至於正斷層及走向滑移斷層產生的機制可能為海岸山脈斜碰撞中央山脈時產生局部的伸張-橫移構造，因而造成了幾組共軛破裂面，是以正斷層及走向滑移斷層的型態產生。而呈現垂直分佈的正斷層，其形成的機制可能與流體通過的路徑有關。在整個地體架構上，本研究認為中央山脈西翼底下的水平地震群，可能為滑脫面前緣，但在中央山脈核心底下的地震群則呈現了垂直分佈並穿透了此滑脫面延伸至20公里處。

We try to analyze the seismotectonics of southern Central Range by earthquake relocations, earthquake focal mechanisms and stress inversion. After 3-D earthquake relocations, we find the seismicity of southern Central Range are apparently different before and after Chi-Chi earthquake, and there are several clusters occurring in this region. Before Chi-Chi earthquake, the distributions of earthquakes appeared with strike near NW-SE and N-S; after Chi-Chi earthquake, it transferred to strike near NW-SE and E-W.
The focal mechanisms are composed of almost normal faults and strike-slip faults, and a few thrust faults. The strike of fault plane which were near NW-SE, N-S and E-W coincides with the distributions of earthquakes. Through stress inversion, we can see NE-SW extension in the area, and it might be related to regional stress.
We suggest that the normal fault and the strike-slip fault were due to partial transtension from Coastal Range obliquely colliding with Central Range. As regards the existence of vertical normal fault might be related to fluid-driven earthquakes. In this tectonic regime, we propose that the horizontal swarms below western Central Range are the detachment. The vertical swarms below the core of Central Range pierce the detachment and extend 20 km under neath.

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