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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/71607


    Title: 利用複反射衰減方法提高海上震測成像並探討南琉球隱沒系統;Improving the seismic imaging in the southern Ryukyu subduction system by using multiple attenuation methods
    Authors: 呂奇祝;Lyu,Ci-Jhu
    Contributors: 地球科學學系
    Keywords: 複反射衰減;莫荷面邊界;琉球隱沒系統;Multiple attenuation;Moho boundary;Ryukyu subduction system
    Date: 2016-07-12
    Issue Date: 2016-10-13 13:22:14 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 南琉球隱沒系統位於菲律賓海板塊(PSP)與歐亞板塊(EUP)交界,在過去的歷史上有大地震發生甚至引發海嘯,因此,瞭解此地區的地體構造是很重要的。在前人研究中,菲律賓海板塊隱沒的地球物理資料並不十分的多,對於菲律賓海板塊隱沒到歐亞板塊的詳細的地體形貌仍未完全掌握,所以本研究利用高解析度的震測影像資料希望能提供更多的資訊。然而,海洋震測影像時常會受到複反射的影響而使深部地殼影像受到干擾。因此,為了得到板塊邊界及莫荷面反射的成像,本研究採用不同去除複反射方法提高深部地殼訊號。資料來源是2009年TAIGER計畫中在南琉球施測的多波道震測剖面(MGL0906_18N;MGL0906_15N;MGL0906_30A),施測規劃為測線每50公尺一個炸點,受波器每12.5公尺一個,共深點(CDP)是6.25公尺,紀錄時間15秒。震源是低頻訊號(20Hz~60Hz),能穿透淺層沉積物,反射深部的地殼訊號。因為複反射會影響深部構造的訊號,因此本研究利用震測軟體處理,使用各種方法去除或減弱複反射效應,提高莫霍面的訊號達到我們的研究目的,提供琉球海域高解析度的地球物理數據。本研究使用四種方式去除複反射。第一,利用消除海表面造成的複反射(SRME);第二,利用Radon轉換減弱複反射;第三,預測解迴旋(Predictive Deconvolution);第四,傾角濾波去除複反射。經過這些步驟,增積岩體和弧前盆地下方的地殼反射訊號清楚成像。此成效可被應用於其它琉球隱沒系統的震測剖面中,在未來可以更瞭解此地區隱沒的邊界狀況。;The southern Ryukyu subduction system is located at the boundary between the Philippine Sea Plate (PSP) and the Eurasian Plate (EUP). The Philippine Sea Plate subducts northwestward beneath the Eurasian Plate near the eastern offshore of the Taiwan orogen. The Ryukyu subduction system is potentially hazardous in terms of tsunami and ground shaking for Taiwan region. Therefore, it is important to understand the crustal structure of this subduction system. In previous studies, the geometry of the subducting PSP is not clear, so we want to process high-resolution crustal-scale seismic images. However, crustal reflections are usually covered by the multiples from sea floor. In order to imagine the plate boundary or even moho reflection, the advanced multiple attenuation methods need to be applied for studying the crustal deformation in the subduction zone. In this study, we applied the multiple attenuation methods to the multi-channel seismic profiles (MGL0906_18N;MGL0906_15N;MGL0906_30A) in the southern Ryukyu subduction system from TAIGER (Taiwan Integrated Geodynamic Research) project in 2009. The field experiment parameters are 50 m shot interval, 12.5 m spacing for the hydrophone, 15 s of recording time, and 6.25 m of CDP spacing. In those profiles, the top of subducting crust of the Philippine Sea Plate is hidden by the multiples. Due to multiples affect on the deep structure signals, we use several de-multiple methods to remove the multiple effects, and increase signals from deep crustal reflectors. In this study, four steps of multiple attenuation methods are used (1) 2D Surface Related Multiple Elimination (SRME), (2) Radon Transform multiple attenuation, (3) Predictive Deconvolution, (4) Dip filter. After these steps, the top of subducting plate below the accretionary prism and the east Nanao basin is clearly imaged. Those methods can be applied to other marine seismic profiles in the future.
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