- 學位論文
全球中大規模地震有限斷層逆推之系統開發
Development of automatic finite-fault source inversion for global moderate-large earthquakes
摘要
全球地震災害頻繁，快速評估中大規模地震 (Mw ≥ 7.0) 之滑移分佈能夠對災害的應變措施作出重要貢獻，因此迫切需要一套即時系統，在地震發生後迅速回報地震的破裂情形。本研究針對全球中大規模地震，發展出一套有限斷層震源快速離線逆推系統。本系統依據全球地震矩張量計畫 (Global Centroid Moment Tensor Project, GCMT project) 所提供之全球地震即時CMT解，反演所需的震源位置則參考美國地質調查局 (United States Geological Survey, USGS) 之結果，並且透過IRIS底下的fdsnws測站服務自動下載遠震波形。根據GCMT和USGS的震源參數報告，包含地震位置、規模、震源機制解，本系統能夠自動地快速判定斷層面之大小、波形時間窗長度與揚起時間。在有限斷層震源逆推時，本研究採用單一斷層面，且允許滑移角度改變，並利用廣義射線理論計算每一個子斷層對地震測站之格林函數。本系統的主要目的是：(1) 提供同震滑移分佈情形之快速解；(2) 找出最大滑移在斷層面上之位置。本研究之系統已經成功地對過去全球十八個中大規模地震進行離線測試，並且將逆推結果跟USGS的結果比較，皆得到一致的特性。本系統的計算時間上，亦比USGS存在優勢，在獲得震源參數和地震波形後，系統僅花40分鐘就能把初步的滑移情形計算出來。
並列摘要
Rapid estimation of the spatial slip distribution of moderate-large earthquake (Mw ≥7.0) is essential for emergency response. It is necessary to have a real-time system to provide the report immediately after an earthquake happens. In this study, we develop a finite fault source inversion offline system for the global moderate-large earthquakes. The global earthquakes activities can be monitored by Global Centroid Moment Tensor (GCMT) project which provides the rapid focal mechanism and the source location can be referred to United States Geological Survey (USGS). The teleseismic waveforms were accessed from fdsnws-station service automatically. According to source parameter (location, magnitude, focal mechanism) from USGS and GCMT report, our system automatically determines the fault dimension, record length, and rise time. We adopted one segment fault plane with variable rake angle. The generalized ray theory was applied to calculate the Green’s function for each subfault. The primary objective of the system is to provide the first order image of coseismic slip pattern and identify the centroid location on the fault plane. The performance of this offline system had been demonstrated by several global big earthquakes occurred successfully. The results show excellent data fits and consistent with the solutions from USGS finite fault inversion results. The computing time of our system is less than USGS and preliminary spatial slip distribution will be provided within 40 minutes.