本研究選取中央氣象局地震觀測網所紀錄921集集地震主震前20個月至主震後3個月內290個地震紀錄，分析主震及餘震區附近(北緯23°至24.5°，東經120°至121°)t*的時空變化。使用單站單相位波譜衰減法擷取P波波相求得觀測t*值。將震源分成三個深度以分析不同深度的路徑之衰減時間項(t*)隨時間變化情形，比較各測站在震前及震後t*平均值變化情形。結果顯示：1從t*分佈發現大區域場址效應可分三區：(1).車籠埔斷層地面破裂帶附近 (2).車籠埔斷層地面破裂帶南方 (3).中央山脈區域(阿里山及玉山測站)。2車籠埔斷層地表破裂帶東南方衰減強度變化較大。3影響車籠埔斷層地表破裂帶北方衰減強度變化的異常體約在5～10km深，向南異常體逐漸深入10～15km。4車籠隆埔斷層地表破裂帶南端及北端測站，在主震前一年，有t*的異常增高現象。

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