在觀察集集大地震前半年的地震活動時，發現集集大地震前15個小時和前4個月分別出現了一條瞬時地震鏈與一條包含了規模5以上的事件、規模4以上的事件以及規模3以上的事件的強地震鏈。推測是大地震前，因地殼處於應力集中的狀態，造成局部的弱化以及地殼整體平衡的改變，因而在其後的一段時間內產生了巨大能量釋放的大地震。 我們研究從1974年1月到2016年4月之間的強地震鏈與大地震之間時間和空間關聯。發現除了集集大地震外，台灣本島及東部沿岸64個規模大於5.7的大地震中有超過六成的大地震在發生前6個月時間內形成了強地震鏈。反過來，我們也透過對強地震鏈的發生位置分析中，發現當產生某個強地震鏈時，能從這個強地震鏈所在的位置推估下一個強地震鏈或是大地震可能發生的位置。進而確認未來的6個月之內是否會產生一個對台灣本島居民有影響的地震活動(大地震或強地震鏈)。除此，我們也發現當某個大地震或強地震鏈發生在東經122.5度以東時，其後的6個月內接續發生的第一個地震活動在近海區域和本島的比例相當的高。 因此，我們透過對強地震鏈的分析，能夠獲得後續大地震發生的位置與時間的資訊。 ;A special phenomenon before the Chi-Chi earthquake in Taiwan was found when we analyzed the earthquake catalog of Taiwan. Namely, there were some ‘‘long shallow vertical chains of earthquakes’’ containing earthquake events with M<5.7 occurred before the Chi-Chi earthquake. The term ‘‘vertical chain of earthquakes’’ stands for a special set of events which happen within a certain short period of time on a vertical line underground. And the term ‘‘long shallow vertical chain of earthquakes’’ stands for the particular vertical chain of earthquakes which contains more than nine events distributed more than ten kilometers under and near the ground surface. A special type of long shallow vertical chain of earthquakes is studied in details. A chain of this type contains at least one event with magnitude higher than 4.8, one event with magnitude higher than 4 and one event with magnitude higher than 3. We analyze this type of chains happened in Taiwan over the last forty years. It is found that, if one (or more than one) of this type of chains has formed in Taiwan then there is a chance that an event with magnitude over six will happen within a short period of time. As a result, the appearance of this type of shallow vertical chain of earthquakes in Taiwan might be considered as a useful information for us to deal with a strong earthquake which may happen in the near future.
