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Author: 陳奕尹
Chen, I-Yin
Thesis Title: 利用經驗格林函數探討重複地震破裂特性
Investigation of Rupture Process of Small Repeating Earthquakes
Advisor: 陳卉瑄
Chen, Hui-Hsuan
金亞伊
Kim, Ah-Yi
Degree: 碩士
Master
Department: 地球科學系
Department of Earth Sciences
Thesis Publication Year: 2017
Academic Year: 105
Language: 中文
Number of pages: 88
Keywords (in Chinese): 斷層嵌塊重複地震經驗格林函數
Keywords (in English): asperity, repeating earthquake, empirical Green’s function
DOI URL: https://doi.org/10.6345/NTNU202202811
Thesis Type: Academic thesis/ dissertation
Reference times: Clicks: 113Downloads: 9
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  • 斷層面上的滑移量分布,反應單一地震發生時,斷層面破裂的動力行為,因此本研究利用利用重複地震的波形相似特性,以有限斷層逆推法計算中小規模地震的震源破裂模型,目的在了解斷層嵌塊中滑移量的空間分布特徵及其控制因子。本研究使用重複地震序列中規模較小的事件作為經驗格林函數(eGf),對較大的目標事件(target event)解迴旋,以求得震源時間函數及進行滑移量逆推,除了討論重複地震的震源特性和其復發週期的關係,並嘗試理解平均和最大滑移量與地震規模的相依性。
    本研究選用一個規模3.4-3.5的準週期性序列(Quasi-periodic Sequence, SQ),發震週期約三年;另一個為非週期性序列(Aperiodic Sequence, SA),發震週期由數分鐘至三年左右不等,研究中發現,SQ中每個事件的最大滑移量主要集中於兩個斷層嵌塊,破裂的區域在空間分布上高度重疊;SA在2009年規模6.9的花蓮地震後數分鐘至數十分鐘內,連續發了三個規模4.0-4.6的事件,由於受到震後滑移速率影響,其滑移分布呈現各自不同的破裂位置與型態,具有高度的異質性。不同週期特性的重複地震序列表現了迥異的破裂行為,可能說明當滑移速率改變重複地震之週期特徵時,也影響了斷層嵌塊本身的異質性,這兩個序列的比較,說明了震源特性和地震的週期行為的相依性。
    此外,我們從全台灣規模3以上的重複地震目錄共62個序列中,篩選出13個序列、共23個規模3.3-4.9的事件進行逆推計算,發現其符合以圓形斷層(circular fault)為基本假設,推導之滑移量與地震矩的關係。本研究計算之平均滑移量約1.74-26.85 cm,其與規模呈現D ∝ Mo2/5線性關係,近似於理論平均滑移量得到之D ∝ Mo1/3的線性關係,且平均滑移量略大於理論平均滑移量,反映了在計算過程中,由於考慮可信度較高的破裂面積,導致滑移量比理論值高;而逆推之平均滑移量與理論滑移量差距越大,代表滑移量在斷層嵌塊上的集中程度越高。在不同地區跨規模的滑移量與地震矩的分析,我們發現規模2的重複地震事件表現出與地震矩的弱關聯性,本研究推論其與無震滑移的貢獻度有關,規模越小的重複地震事件,周圍無震滑移區域的範圍越大,使滑移量在斷層嵌塊上高度集中,亦導致逆推得到的地震滑移量未呈現D ∝ Mo1/3的線性關係。

    Using small earthquakes as empirical Green’s functions (eGf), we apply a finite-source inversion to demonstrate a link between slip heterogeneity and earthquake recurrence of two repeating sequences in eastern Taiwan. The M3.4–3.5 quasi-periodic repeating earthquakes that are characterized by 3-yr recurrence interval reveal overlapped slip concentrations. These obtained models show peak slip of 6.70-17.48 cm. Under the influence of nearby M6.9 event, the M4.0-4.6 repeating earthquakes that are separated only by 4-88 mins, reveal an aperiodic manner. Inferred slip behaviors perform not only a distinct rupture characteristic without overlap in the slip areas, but an inconsistent slip distribution compared with pre-M6.9 repeating earthquake. The variation of rupture behavior suggests the temporal change of loading rate caused by the nearby large earthquake may change the slip heterogeneity in a repeatedly ruptured asperity. We also study repeating earthquake sequences with a greater range of magnitude for slip inversion. Slip heterogeneity, as a result of heterogeneous stress accumulation on a fault, may rely on the stress condition in each subarea of the fault plane, whereas stress condition inside the asperity controls where the peak slip takes place. A collection of slip heterogeneity in different events therefore, will have potential application in monitoring the temporal evolution of stress state.

    致謝 I 中文摘要 III ABSTRACT IV 目錄 V 圖目錄 VII 表目錄 IX 第一章 研究動機 1 第二章 前人研究 3 2.1 重複地震的發現 3 2.2 經驗格林函數與有限斷層逆推法 4 2.3 重複地震的尺度關係 6 2.4 重複地震的破裂特徵 14 2.5 重複地震與大地震的關係 18 第三章 資料與研究方法 22 3.1 經驗格林函數之選定 22 3.1.1 全台灣重複地震序列 22 3.1.2 目標事件與經驗格林函數選取方法 26 3.2 疊代解迴旋法 29 3.3 逆推方法 31 3.3.1 有限斷層逆推 31 3.3.2 計算平均滑移量 32 第四章 研究結果 34 4.1 求取最佳震源參數 34 4.1.1 孕震時間與破裂速度之選定 34 4.1.2 平滑化參數之選定 36 4.1.3 滑移量與震源參數的關係 37 4.2 重複地震事件之破裂模型 41 4.3 不同週期特徵之重複地震事件破裂模型 43 第五章 討論 49 5.1 重複地震序列之破裂特徵與週期特性的關係 49 5.2 重複地震之滑移量 55 5.2.1 理論滑移量 55 5.2.2 台灣重複地震之平均滑移量 55 5.2.3 其他地區觀測之重複地震滑移量與規模的關係 58 5.3 重複地震的應力降 63 5.4 資料與方法的限制 67 5.4.1 經驗格林函數的使用限制 67 5.4.2 有限斷層逆推法的限制 68 第六章 結論 70 參考文獻 72 附錄 77

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