集集地震後距車籠埔斷層東方60公里出現一條N20°E走向地震帶，寬約10公里，長約80公里，其發生位置位於東部中央山脈東翼與西翼的地質分界線上，求取其震源機制主要為正斷層。我們藉由研究分析此地震帶的地震活動性與震源機制和應力場變化，以求瞭解此區域的地震活動與地體構造的關係。
研究結果顯示：集集地震前中央山脈東側水平向應力為主的逆斷層型態於集集地震後三個月內被山脈西側的正斷層型態所取代，屬於垂直應力為主的應力場，之後一年內側向壓應力再度累積，正斷層逐漸減少，一年後回復至集集地震前山脈東側之逆斷層為主的型態。此種正斷層與逆斷層的轉換應為板塊內部的壓縮應力釋放再累積所造成。
集集地震後中央山脈產生的正斷層沿著高角度斷層面而產生，反應集集地震後造成車籠埔斷層上盤後方淺部地殼應力的轉換，表現了台灣東部中央山脈快速塌陷的模式。
關鍵字：集集地震、山脈塌陷、震源機制、應力反演。

After 1999 Chi-Chi earthquake, a 10 km wide and 80 km long seismogenic belt appeared with strike N20°E, and located 60 km east away from Chelungpu fault. The seismic belt is located at the geological boundary seperating east and west Central Range. We try to analyze the seismicity by using earthquake relocatons, earthquake focal mechanisms and stress inversion.
Our result shows : (1) 3 months to one year after Chi-Chi earthquake, the main horizontal compressional stress under east flank of Central Range before Chi-Chi earthquake change to vertical principal stress axes σ1 under the boundary line between the east and the west flank of Central Range. (2) one year later the stress under Central Range return to the situation before Chi-Chi earthquake.
The compression-to-extension process demonstrates stress rotation in the shallow crust under Central Range before and after Chi-Chi earthquake, and offer a modern mountain collapse model in Taiwan orogen.

Key words: Chi-Chi earthquake, mountain collapse, focal mechanisms, stress inversion.

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