利用GPS與InSAR觀測資料及塊體模型探討台灣西南部活動斷層的震間行為;Intreseismic fault behavior in southwestern Taiwan from GPS and InSAR observations and block model

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Title:	利用GPS與InSAR觀測資料及塊體模型探討台灣西南部活動斷層的震間行為;Intreseismic fault behavior in southwestern Taiwan from GPS and InSAR observations and block model
Authors:	蕭立揚;Hsiao, Li-Yang
Contributors:	地球科學學系
Keywords:	台灣西南部;活動斷層;全球定位系統;合成孔徑雷達干涉圖;塊體模型;GPS;InSAR;Taiwan;block model;active fault
Date:	2020-08-20
Issue Date:	2020-09-02 15:42:11 (UTC+8)
Publisher:	國立中央大學
Abstract:	台灣位處板塊邊界，受到菲律賓海板塊向歐亞大陸板塊快速聚合的影響，有分佈密集的活動斷層與頻繁的地震。近十年以來又以台灣西南部地區在2016年發生的美濃地震造成的災情最為嚴重。本研究針對中央地質調查所公佈，位於台灣西南部地區的8條活動斷層，利用衛星、雷達資料及三維塊體模型方法DEFNODE估算其震間活動情形，以協助地震災害風險之評估。為觀察斷層的震間滑移隨時間改變的差異，以2016年美濃地震為分界，本研究將2002年至2019年所累積的GPS觀測資料分為代表發震前2002年初至2015底與可能受到震後影響的2016年初至2019年9月底等兩組資料。此外本研究亦嘗試在三維塊體模型中引入鉛直向GPS與PS-InSAR資料，希望能夠藉此分析高傾角斷層造成的地表抬升與下陷。模型結果顯示，在美濃地震前後，左鎮、旗山與恆春斷層的平均滑移速率有大於10 mm/yr的差異，且其中左鎮與旗山斷層僅與震央相距十幾公里。雖然目前無法確認滑移速率的改變是否與地震事件有直接關聯，但本研究已成功觀察到斷層活動情形隨時間的改變的現象。GPS及PS-InSAR資料聯合反演模型的結果則顯示，鉛直向GPS速度資料可能受到過多斷層活動以外的事件影響，難以被塊體模型所擬合，也因此鉛直向GPS速度資料對斷層滑移速率估算的影響非常有限。另一方面，PS-InSAR資料僅在左鎮斷層周邊有較大的殘差分佈，與GPS資料整合時的修正值很可能是此殘差分佈的主因。斷層滑移速率之結果則顯示，PS-InSAR資料可以協助降低僅用GPS觀測資料時被高估的斷層滑移速率。整體來說，本研究認為在引入鉛直向地表變形時，須注意模型擬合結果與殘差分佈，避免受到過多非斷層活動之地表變形的干擾。 ;Located on the plate boundary between the Philippine Sea Plate and the continental margin of Eurasian Plate, Taiwan has experienced rapid convergence which leads to densely distributed active faults and frequent earthquakes. In the past ten years, for example, the 2016 Meinong earthquake occurred in southwestern Taiwan caused the most serious disaster. This study focused on analyzing eight active faults in southwestern Taiwan published by the Central Geological Survey. By integrating GPS and PS-InSAR data and implementing the three-dimensional block model method DEFNODE, this study estimated the interseismic slip rates of these faults that can be further applied to the probability seismic hazard analysis. Different form previous interseismic block models that primarily used average horizontal velocities, this study tried to incorporate PS-InSAR and vertical GPS data to model the interseismic surface uplift or subsidence caused by dip-slip faults. Results show that the GPS vertical motion was poorly fitted by block models, which may be due to unmodeled non-faulting mechanisms such as active folding. Integration of GPS and PS-InSAR observations, on the other hand, can notably affect the modeling results where velocity residuals were greatly reduced and long-term slip rates on some faults become more reasonable than the GPS-only results. This study further examined possible influence of the 2016 Meinong earthquake on interseismic slip rates of adjacent faults by dividing the GPS data into two groups: the “pre-Meinong” data from 2002 to 2015 and the “post-Meinong” data from 2016 to September 2019. Results show that slip rates of the Zuozhen, Chishan and Hengchun faults are more than 10 mm/yr faster than those before the earthquake, where the Zuozhen and Chishan faults are only 10-20 km away from the epicenter. Although whether these changes in slip rates are directly related to the Meinong event remains debated, the model results reveal possible temporal variations of fault behavior.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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