台灣西南部衰減模式分析;The Analysis of Three-Dimension Attenuation Tomography in Southwestern Taiwan

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Title:	台灣西南部衰減模式分析;The Analysis of Three-Dimension Attenuation Tomography in Southwestern Taiwan
Authors:	陳昭邑 Chen, Chao-Yi
Keywords:	衰減;影相層析;attenuation;tomography
Date:	2020-07-24
Issue Date:	2020-09-02 16:15:18 (UTC+8)
Abstract:	本研究藉由研究台灣西南部的衰減模型（Q-1，Q：品質因子）來了解當地的構造特徵。衰減(attenuation)是了解地球內部構造的重要物理參數，但由於地震資料的缺乏，過去一直無法在台灣西南部得到解析度足夠的衰減模型。2010年，甲仙發生了西南台灣相隔46年的規模6以上的大地震，之後又相繼發生了2012霧台地震及2016的美濃地震，豐富了此區的地震資料，也提供我們進一步了解台灣西南部構造的可能性。本文的研究區間在東經120°至121°，北緯22.3°至23.3°。我們使用1991至2016年間的ML 3.5至5.5的TSMIP資料進行分析，在ω2-source model以及Q與頻率無關的假設下，使用格點搜尋(grid search)找到其對應的總路徑衰減運算子(t-operator)。有了t與已知的三維速度構造，利用區域性地震影像層析法 (local earthquake tomography, LET) 即可得到三維Q模型。在研究中，我們分別嘗試了網格間距10公里及5公里的模型，以期達到穩定模型與構造研究的平衡。研究結果顯示此區的地震集中在深度25公里以內的QP和QS (QP：由P波所得之Q；QS：由S波所得之Q) 高區，這些高Q的地區大致位於西部麓山帶。深度5公里時在東經120.5°的附近有一片低QP值的區域可反映出高雄基盤的位置。在柴山地區淺層的高雄石灰岩可能導致了當地的高QP、QS數值。在此區龍船斷層、旗山斷層等斷層兩側皆可發現Q值的側向變化。在2016美濃主震以西的淺層可看到一低QP、QS跟高QP/QS的區域，可能是因高孔隙液壓的古亭坑泥岩所導致。 ;We used waveform data from Taiwan Strong Motion Instrumentation Program (TSMIP) to analyze the attenuation property of southwestern Taiwan. The original data is the spectrums of P- wave and S- wave from 1991 to 2016 with ML 3.5 to 5.5. Then we got 324 events for QP and 394 events for QS. First, we used grid search to determine t* by assuming a ??2-source- model and a frequency-independent Q. The corner frequency of each event was fixed, and we defined a quality index to weight data for the inversion. Finally, we got QP and QS model of southwestern Taiwan by Local Earthquake Tomography (LET). The results show that high Q region with higher seismicity which is located in Western Foothills and the low QP area in 5 km depth implies the position of Kaohsiung basement. The Kaohsiung limestone contributes to the high Q in the shallower part of Shoushan. The lateral Q variation is observed in many faults. Our results imply that there is a high fluid pressure zone with low Q and high QP/QS above the hypocenter of the 2016 Meinong earthquake. On the other hand, a low fluid pressure zone with high Q and low QP/QS exists beneath the hypocenter.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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