| 摘要: | 本研究利用接收函數推求台灣南部莫荷面深度，使用兩次TAIGER計畫在南部所設置寬頻地震站(TAIGER I在2006至2007年間在南北向南段測線的5個測站、TAIGER II在2009年在南南段中間山區的3個測站)，加上氣象局地震觀測網(CWBSN)在南部的7個測站，範圍包括了高雄、屏東至台東，使測區範圍更為完整。地震資料的選取採預震央距介於30至90度且規模大於6.0以上的地震事件。資料分析使用Levin and Park (2000)所提出多重窗制相關估計法(Multiple-Taper Correlation estimate, 簡稱MTC)，求得徑向接收函數；由徑向接收函數推估測站下方莫荷面深度則使用Zhu and Kanamori (2000) 所提出H-κstacking方法，求取莫荷面深度與κ值(即Vp/Vs)。根據研究結果顯示，可以發現從西部麓山帶莫荷面深度介於30-35公里間，往東進入中央山脈主稜，莫荷面漸深達到40公里左右，到中央山脈東測深度漸漸變淺，到位在海岸山脈的FULB站，莫荷面深度突然變淺，約在16公里，與海洋地殼厚度相近，顯示縱谷以東已進入菲律賓海板塊範圍。此外，比較前人研究速度模型與密度模型、前人接收函數相關研究、地震事件後方位角分群計算的結果，本研究可歸納以下結論：1.莫荷面深度分佈與謝獻祥(2009)利用重力逆推之密度模型結果最為符合，速度模型中與Cheng(2008)在台灣東南部速度模行趨勢較為相近；2.與Wang et al.(2010)所發表的莫荷面起伏最為相近，本研究加上了山區測站，結果應更接近實際莫荷面起伏；3.依後方位角(bazk azimuth)分群作計算，所得到的深度與未分群之結果並無顯著差異。In this study, we figure out the Moho depths in southern Taiwan by using receiver function. The sources of the data are from TAIGER project and Central Weather Bureau Seismograph Network (CWBSN). And we use five broadband seismic stations of TGS-line of TAIGER I, seven stations of CWBSN from 2006 to 2007 and six broadband seismic stations of SS-line of TAIGER II at 2009. The coverage of these stations includes Kaohsiung, Pingtung, Taitung. From these stations, we pick up the earthquake events whose epicenters and magnitudes are between 30 to 90 degree and greater than 6.0, respectively. In aspect of data analysis, the Multiple-Taper Correlation estimation is used calculating the radial receiver function in the first step. Then, we compute the possible Moho depth and κ value (Vp/Vs) by H-κ stacking. The results indicate the Moho depths in the western foothills are approximated 32 to 35 km. And it gradually becomes deeper in the Central Mountain Range, around 35 to 40 km. For station TGS12, the depth is 40 km, it is the deepest in this study. The Moho depth beneath FULB is 16 km, and it indicates that FULB, east of the Longitudinal Valley, is located above the Philippine Sea Plate. According to further analysis and discussion with former researches, we can have the following conclusions: (1)Comparing the result with former three velocity models and one density model, our result is mostly consisted with the density model proposed by Hsieh(2009) and in velocity model is Cheng(2009). (2)Comparing the result with former studies about receiver function in Taiwan, our result is most similar in Wang et al(2010). (3)We re-group the events by back azimuth into four quadrants and get the similar Moho depths as previous ones. |
