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: 113 Downloads: 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.
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