印尼蘇門答臘隱沒帶之震波衰減特性;Characteristics of Seismic Attenuation in Sumatra Subduction Zone, Indonesia

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Title:	印尼蘇門答臘隱沒帶之震波衰減特性;Characteristics of Seismic Attenuation in Sumatra Subduction Zone, Indonesia
Authors:	斯亞萬;Styawan, Yudha
Contributors:	地球科學學系
Keywords:	品質因子;衰減;蘇門答臘隱沒帶;板塊撕裂;quality factor;attenuation;Sumatra subduction zone;slab tear
Date:	2021-11-12
Issue Date:	2021-12-07 11:51:50 (UTC+8)
Publisher:	國立中央大學
Abstract:	已有研究成功地利用局部或區域性地震資料分析震波衰減特性，尤其是在隱沒帶，其對高溫與流體飽和度敏感的能力有助於理解隱沒帶之構造。在本研究中，我們嘗試利用此種方法來關注蘇門答臘隱沒帶震波衰減的一般性特徵，特別像是與板塊撕裂的此種物理性質之相關性。震波衰減是指當地震波通過介質時的能量損失，以品質因子（Q）表示且成反比關係，震波衰減的發生是因一些能量在傳播的過程中轉化為熱或當震波通過不同特性的材料時被反射和折射所影響。本研究利用印尼氣象、氣候與地球物理局（BMKG）安裝在蘇門答臘各地的38個地震站，在2013年1月至2018年7月的寬頻地震資料，共271起事件，深度範圍100至350公里，地震規模介於3.9至6.5。拐角頻率和震波衰減分開處理以避免震源和路徑參數間的互償效應。為考慮場址放大因子，我們透過矩陣方法，假設衰減和頻率無關的情況下嘗試擬合觀測和計算的位移譜，以求解每個測站的衰減參數。結果顯示澳洲板塊隱沒至蘇門答臘之下的區域表現出相對高的Q值，Qp與Qs 分別約 677和 776；相比之下，地函楔形體表現顯著而相對低的Q值。這是隱沒帶常見的地震學特徵，冷卻的緻密岩石圈板塊隱沒至地函中，地函楔形體可能反應板塊脫水作用。在前弧測站所記錄的高Q值區域中，一些異常的低Q值存在於北蘇門答臘，尤其是與多巴湖底下重合的區域，這可能成為板塊撕裂存在的額外證據。這個板塊撕裂的結果可能增加熔化作用的活動，多巴湖周圍群山的測站所記錄的低Q值區域揭露了這項特性。;Seismic attenuation, especially in subduction zones, has been studied successfully by some previous studies using local or regional earthquake data. The capability of being sensitive to the high temperature and fluid saturation could help understand the subduction zone structure. In this study, we attempt to use this method to focus on the general characteristics of seismic attenuation in the Sumatra subduction zone and correlating to the physical properties such as slab tear in particular. Seismic attenuation refers to the energy loss of seismic waves while propagating on a medium, represented by the opposite of quality factor (Q). Seismic attenuation could occur because some of the energy may convert into heat during propagation or be reflected and refracted while passing through materials with different properties. This study utilizes broadband seismic data from 38 stations of the Meteorological, Climatological, and Geophysical Agency of Indonesia (BMKG) that are located throughout Sumatra, collected from January 2013 to July 2018. It has 271 events around 100 - 350 km depth with magnitude ranges between 3.9 and 6.5 Mw. Corner frequency and seismic attenuation are processed separately to avoid the trade-off between source and path parameters during the data processing section. To consider the site amplification factor, we solve the attenuation parameter for each station by using a matrix approach and try to fit between the observed and calculated displacement power spectra, assuming that the attenuation is frequency-independent. The results indicate that the Australian slab sunk beneath Sumatra signifies a relatively high-Q zone, around 677 and 776 for Qp and Qs, respectively. In contrast, the mantle wedge has a significant low-Q value. It is a common seismological characteristic in the subduction zone where the cooled dense lithospheric plate is subducted into the mantle, whereas the mantle wedge may reflect the slab dehydration. In the high-Q zone recorded in fore-arc stations, some lower-Q anomalies exist in northern Sumatra, especially coincide with the area beneath Lake Toba, which could be additional evidence to the existence of the slab tear. The consequence of this slab tear, which may increase the active melting, is revealed by the lower-Q zone recorded in the stations of the mountains around Lake Toba.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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