餘震誘發與斷層面應力轉移之檢測－－以集集地震為例

The Testing of the Aftershocks Triggered and Stress Transfer on the Fault Planes: Case Study of 1999 Chi-Chi Earthquake

大地震發生後，探討震後應力轉移誘發餘震，已經成為地震學中相當重要的問題，許多地震學家已經做了相當多的研究。其中，描述應力轉移的物理量，通常是以震後庫倫應力變化來表示，庫倫應力增加使得區域應力增加，也增加了誘發餘震的機率。經過許多學者的研究，結果證明，許多餘震的誘發確實是發生在庫倫應力增加的區域，這個結果也同時驗證應力轉移的事實。關於應力轉移與餘震誘發的研究，以往大多是以統計餘震落在庫倫應力增加區的方式來分析，並未對發生餘震的斷層面上庫倫應力變化，確實的計算，因此本研究將以集集地震為例，確實計算餘震斷層面上庫倫應力變化，來檢視誘發的原因。本研究選取集集地震後2個月內6個規模（Mw）大於6.2的餘震來分析，計算集集地震後的應力轉移，結果發現6個目標餘震斷層面上的庫倫應力變化值都有分佈大於1bar的區域，根據前人的研究，要發生誘發地震，斷層面上的庫倫應力變化必須大於1bar，因此證明本研究所選取之餘震皆由集集地震同震應力轉移所誘發。

After the great earthquake happened, investigating of the stress transfer which triggering aftershocks, has become a very important issue in the seismology. Many seismologists have done quite lots of research. In these studies, they usually use the Coulomb failure stress changes to describe stress transfer. Coulomb stress increase makes the regional stress increases, also increases the probability of aftershocks induced. After these researches, the results proved that many aftershocks triggered indeed occurred in the area of Coulomb stress increase, the results also verify the facts of the stress transfer.About of the study of stress transfer and aftershocks triggered, in the past, these problems are always analyzed by the statistics method. They did not calculate the ΔCFS values on the fault planes of the aftershocks. Therefore, this study will case by Chi-Chi earthquake indeed to calculate the Coulomb failure stress changes on the fault plane for checking the triggering reason. This study selected 6 aftershocks of Chi-Chi earthquake in two months which magnitude greater than 6.2 to analyze. The results showed that, after stress transfer, all of the 6 fault planes of aftershocks with distribution area greater than 1bar of Coulomb failure stress change. According to previous studies, if the triggering aftershocks happened, the fault plane must be greater than 1bar of Coulomb failure stress change. Therefore, the results prove that all of the selected 6 aftershocks in this study are triggered by the coseismic stress transfer of the Chi-Chi earthquake.