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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5525


    Title: 利用RTL (Region-Time-Length) 演算法 探討921 集集大地震之前兆現象;+C3677An improved region–time–length algorithm applied to the 1999 Chi-Chi, Taiwan earthquake
    Authors: 吳怡萱;Yi-Hsuan Wu
    Contributors: 地球物理研究所
    Keywords: 集集地震;地震寧靜;地震活化;RTL演算法;seismic quiescence;seismic activation;RTL algorithm;Chi-Chi earthquake
    Date: 2006-05-26
    Issue Date: 2009-09-22 09:55:53 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 由於地震是一最不可預測的天災,又其帶給的傷害相當大,所以關於如何 預測及地震前兆成為一項非常重要的課題。兩個在大地震來臨之前的前兆現 象-地震寧靜、地震活化,通過對此兩前兆現象之觀察,或許可進而偵測到 大地震之來臨。所謂地震寧靜:如同其字面意思,在大震來臨之前地震活動 度平均降低,低過整個地震活動度的背景值,這樣的現象乃來自於能量在這 段時期的累積,累積的期間由於沒有釋放出來因此也較少地震產生;相對地, 當能量累積的越多所需時間越久,呈現出的寧靜亦越大,隨之而來的地震也 越大-如同在一些真實地震中看到的現象一樣。在一些研究中,由於地震寧 靜可以指出地震活動度異常的時間及地區而幫助成功預測大地震即將來臨。 地震寧靜與地震活化是一體兩面的,地震活化通常伴隨了地震寧靜而來;這 是一種能量的高級相變,通過了地震活化的轉移,能量達到臨界點釋放而形 成大地震。在針對集集作為例子所用的統計方法-RTL(Region-Time-Length) 演算法中清楚得到了地震活動度在時間上的變化,也確實發現在像集集地震 這樣的特徵地震之前有一段維持長達2?3 個月的寧靜期,隨後而來的是一段 地震活化時期。將寧靜時間主要活動度變低的時間取出作二維分布圖時尚可 發現這些寧靜都發生在集集震央附近;活化時期也可窺見高地震活動度環繞 在集集震央附近。RTL 演算法要有效表示出地震寧靜及地震活化尚且需除去 特徵時間、特徵長度等不安定因素,因為人為選取以上自由參數可能造成RTL 不客觀結果,因此在本研究中更利用計算RTL 間之相關係數取得最佳自由參 數。而最後的結果亦証明了相關係數的演算更完善了RTL 演算法。從前人的 研究及此次研究的結果可以更加確信地震寧靜的偵測,或許將可給予在地震 預測上極大的幫助。 By means of the Region-Time-Length (RTL) algorithm, which is widely used for investigating the precursory seismicity changes in China, Italy, Japan, Russia and Turkey, we examine the precursory seismic activity occurred prior to the 1999, Mw = 7.6, Chi-Chi earthquake around its epicenter. Based on our calculation of the RTL values, the epicentral area has been found to strongly exhibit the signature of anomalous activity, associated with the seismic quiescence and activation, before the main shock. Also proposed in this study is a helpful method for determining two important parameters used in the RTL analysis, the characteristic time and distance. Such method will largely reduce the ambiguity in the original RTL algorithm. The RTL results made from the catalogs with different magnitude range show that earthquake quiescence should be influenced not only by intermediate magnitude earthquakes, but also by smaller earthquakes. The relationship that the RTL value correlated with the square and cube of number of earthquakes implies that the RTL value is not just simply guided by the earthquake number. For testing the statistical significance of our result, we got a probability of 2% of the quiescence anomaly and of 0.5% when constrained that the anomaly occurred 2.5 years before the large Chi-Chi earthquake. We thus proved that the quiescence before Chi-Chi earthquakes is not resulted from the stochastic process.
    Appears in Collections:[地球物理研究所] 博碩士論文

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