| 摘要: | 許多地震發生之後，都可以偵測到重力的改變，這是因為岩層受到應力作用而變形或破裂，使得地表地形及地下構造改變，這些現象都會造成地表重力值的永久性變化。透過精密的重力測量資料，我們可以了解地震對台灣的影響。本研究大致可分為兩個部分。第一部分，利用新竹市十八尖山超導重力儀 (Superconducting Gravimeter，簡稱SG)，所記錄到的實際重力觀測資料 (2006/4-2011/9)，去除各種環境引起的訊號，如：日、月引力產生的固體潮、海潮以及地下水位、氣壓、極移等因素，分析地震前後，因板塊或斷層位移所造成的重力變化。第二部分，使用台灣寬頻地震網 (Broadband Array in Taiwan for Seismology，簡稱BATS)，2006年4月至2011年9月，台灣本島附近，深度小於300公里，地震矩規模 (Mw)大於5的地震資料，配合Fu and Sun (2008)的彈性地球模型，計算各地震所產生的永久重力變化量。此模型可計算地下構造和地表受到地震影響而產生的重力變化。本研究最後比較儀器記錄數據與理論模型計算結果，發現兩者之間結果正負號相同但大小不同，主要原因可能是台灣的地質構造過於複雜，導致模型無法準確估計地震對台灣的影響。
After earthquakes, we can detect the Gravity changes. This is because the rock will deform or brake by tectonic stresses, both them will cause permanent gravity change. Therefore, through the data of precision gravimeter, we can understand the influence of the earthquake on Taiwan. This research is divided into two parts. In the first part, we took gravity data (2006/4-2011/9) from Hsinchu superconducting gravimeter (SG) station, and removed those data we didn’t want such as solid earth tide, ocean tide, polar motion, atmospheric, continental water storage then we had got residual gravity data. Then we used the residual gravity data to compute permanent gravity changes caused by quakes. In the second part, we used earthquakes data which is start from 2006/4-2011/9, near Taiwan, depth around 0 to 300 km, moment magnitude (Mw) greater than 5 from the Broadband Array in Taiwan for Seismology (BATS). Than used Fu and Sun (2008) numerical earth model with earthquakes data from BATS, to compute permanent gravity changes caused by earthquakes.
Finally, we analyzed and compared SG data result with the model computing result. The result show that the sign of two results is the same but the value’s order is quite different. The main reason why maybe is the complicated tectonic in Taiwan. It cause the model could not compute the influence of the earthquake precisely. Complicated tectonic also influence the quality of SG data, although we could get clear signals by many data processes, we could not sure that it is meaning the gravity changed by the earthquake. |
