| 摘要: | 本研究選取中央氣象局1990~2013年地震目錄中，規模(ML)大於6以上的地震做寧靜期檢測與b值特性探討，寧靜期的理論，依據為大地震發生前，地震活動度會相對減小，以孕育出更大的地震，此時的寧靜期可謂時序前兆現象。而b值變化，則由Gutenberg – Richter關係可以推得，b值越小則越有機會發生大地震，b值越大則發生大地震的機會較小，因此b值變化可視為尺度前兆現象。在檢測大地震前是否有寧靜期，並考慮每個地震序列的完備性，每個檢測的大地震，皆取大於最小完備規模(MC)的震前序列來分析。首先對於所有規模大於6的地震，篩選互不干擾的獨立地震事件，共計8個陸域和10個海域地震，從它們震前Z值變化的時間點發現，許多地震Z值變化的原因，為外來大地震的餘震影響，或者是受鄰近地震的干擾，因此，再摒除9個主震不予討論。結果篩選出臺灣地區陸域的目標大地震有3個。皆有寧靜期現象出現，並出現明顯寧靜的事件，其寧靜期長度隨著主震規模大小而增加，而海域大地震的寧靜期現象，則不會發生或無法的清楚顯現。分析18個大地震的b值中，本研究選取二段資料來計算地震發生前b值，一為1980年到目標地震發生前，另一則為每個目標地震前10年資料，計算出b值後，又區分平均b值與震前b值作分析。最後將計算出的4類b值，利用Excel進行線性迴歸，計算各項b值與對應地震規模的相關性，結果發現目標地震發生前10年的平均b值，在海域的地震，其平均b值與地震規模有中度程度的相關，但陸域地震的平均b值以及其他計算方式的b值則與地震規模無明顯相關性。因此，臺灣地區大地震僅陸域地震有寧靜期的時序前兆出現，而平均b值所代表的尺度前兆，則可由目標地震前10年平均b值的海域大地震觀察到。
In this study, we use the complete catalog of Central Weather Bureau earthquake from 1990 to 2013 to talk about the seismic quiescence and the character of b values which earthquake magnitude larger than 6.0. The theory of Precursory Seismic Quiescence is the premonitory symptoms of a big earthquake that the seismicity would reduce relatively so that nurturing greater earthquakes. And the changing of b values could be obtained by the Gutenberg - Richter relationship. Minor b values gives more chance to become a giant earthquake; on the contrary, off chance of becoming that. Consequently, we regard the changing of b values as the prediction of scale.To detect whether the seismic quiescence exists needs to discard the human and mechanical factors. As the result, to ensure the completeness of sample, this thesis will take the earthquakes that well coincides with MC for analyzing. First, for all the samples on the records that ML>6, there considers only main shocks which implies these earthquakes are not involved to each other and had picked out 8 island earthquakes and 10 offshore earthquakes for deeper discussion. According to the timing of Z vales varying before the quakes, there can find out that the varied Z values is due to the aftershocks of external earthquakes or the interference of other quakes nearby. Therefore, the 9 quakes among the 8 island quakes and 10 offshore quakes that mentioned above are omitted, and there are only 3 island quakes remained. Seismic quiescence is emerged and occurring quiescence events; the period of seismic quiescence would be increased by ML. As for the remained offshore quakes, it had no clarified rule to seismic quiescence.Analyzing b values in 18 earthquakes, this study selected two data to calculate the b values of pre-earthquake. One is the mean b values from 1980 to right before objective quake; the other is the objective quake decade data ago. After calculating the b value, but also analyzing by distinguish the average b value and b values of pre-earthquake. In this way, calculate 4 kinds of the b values & linear regression by Excel and find out the relationship of each type of b values corresponding seismic scale, the results found that the average b value of objective earthquake decade ago. There are moderate correlation between the average b value and seismic scale in sea area quakes. On the contrary, the average b value of land quakes have not clear related with seismic scale.In consequence, there are time sequence seismic precursors of seismic quiescence only appears in land quakes in Taiwan, and its seismic scale can be observed by the mean b values of sea area quakes in a decade before objective quake. |
