1999年9月21日發生規模ML7.3的大地震，震央位於南投縣集集地區。該次地震主要為車籠埔斷層之錯動所引起，在斷層沿線及廣大地區造成嚴重的災害與傷亡。無論是野外觀察與GPS資料都顯示車籠埔斷層為一逆衝斷層且具有左向滑移特性，根據豐富的GPS地表位移觀測值以及由中央氣象局各地強地動記錄雙積分後之永久位移量，藉由斷層滑動模型，求得車籠埔斷層之錯動參數。 本研究方法：將車籠埔斷層依位移量大小分為北、中、南三個區段，分別求取各區段斷層錯動參數。最初以二維的斷層滑動模型（Cohen, 1996）決定斷層之傾角、斷層面底邊的深度以及斷層之傾向滑移量。繼之以三維的斷層滑動模型（Okada, 1992）決定其左向滑移量與斷層面之長度。最後，進一步計算車籠埔斷層錯動所造成的地震矩與平均應力降。 本研究結果：北端區段一的斷層平均滑動量為11.7公尺（逆衝量為8公尺，左移量為9公尺），斷層面之長度與寬度分別為23.2公里與20.6公里，傾角為向東29度，本區段的滑動量最大；中間區段二的斷層平均滑動量為7.6公尺（逆衝量為6.5公尺，左移量為5.5公尺），斷層面之長度與寬度分別為13.4公里與20.6公里，傾角為向東29度；南端區段三的斷層平均滑動量為5.4公尺（逆衝量為5公尺，左移量為2.5公尺），斷層面之長度與寬度分別為26.5公里與20.6公里，傾角為向東29度。以上斷層模擬結果與震源機制解相近，計算出之地震矩總和為 - ，以及平均應力降為106.1 bar。 由本研究結果可以獲得下列幾點結論： 1.車籠埔斷層大體上可視為一向東傾斜的平面構造。 2.本研究最初使用簡易的二維斷層滑動模式，以快速決定車籠埔斷層之錯動量。 3.經由地表位移觀測值與計算值之比對，求得斷層滑動面向東下傾約達深度10公里。 4.中央氣象局所定集集主震震源深度為8公里，位於本研究求得斷層滑動面之下。這可能原因為本研究所求得之斷層面過於簡化，或是震源深度可以定淺一些。 5.車籠埔斷層錯動所引起之地下應變場與地下水位觀測井所觀測到的水位變化有顯著的正相關性，即體積膨脹率為正值之地區有地下水位下降現象。反之，體積膨脹率為負值之地區有地下水位上升之現象。 6.由集集大地震餘震之震源機制可以發現，因車籠埔斷層錯動所引起之地表面以下之應變場，在具有正斷層機制區域的應變場並未解除區域性壓應力所導致之逆衝斷層機制。 An earthquake (Mw=7.6, ML=7.3) occurred near the town of Chi-Chi in Nantou County in central Taiwan at 1: 47 a.m., September 21, 1999 (local time). The Chi-Chi earthquake produced a rich set of data on surface deformation caused by dislocation of the Chelungpu fault. This study used analytical formulas for a 2-D fault model(Cohen, 1996) and a rectangular fault model (Okada, 1992) to determine the Chelungpu fault dislocation parameters. We compared both the GPS data and integrated strong motion displacement data with the calculated results from the fault models. The Chelungpu fault was divided into three regions in this study. The fault parameters of Section 1(northern part) are : fault length 23.2 kilometers, fault width 20.6 kilometers, dip angle 29 degrees and vector fault slip 11.7 meters; Section 2 (middle part): fault length 13.4 kilometers, fault width 20.6 kilometers, dip angle 29 degrees and vector fault slip 7.6 meter. Section 3 (southern part) : fault length 26.5 kilometer, fault width 20.6 kilometers, dip angle 29 degrees and vector fault slip 5.4 meters. Using these parameters we can obtain the seismic moment and average stress drop as - and 106.1 bars, respectively. The conclusions of this study can be summarized as follows: 1. The Chelungpu fault can be approximated as a simple plane and dipping east. 2. By using a simplified 2-D model we can determine the fault dislocation parameters rapidly. 3. The fault was dipping east and reached a depth of 10 kilometers by comparing the observed and calculated data. 4. The hypocenter of Chi-Chi earthquake was 8 kilometers (CWB), this location is below the fault plane found in this study. This could because our fault slip model is too simple or the depth of hypocenter should be shallower. 5. The co-seismic deformation caused strain changes below the earth surface. We can correlate these strain changes with water level changes during earthquake. There is positive correlations between volume dilatation or contraction and water level changes. 6. From the focal mechanisms of Chi-Chi aftershocks we can find that the stress changes of the Chelungpu fault slip didn’t release completely the regional compressional stress.
