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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/44437


    Title: 由西太平洋地區T波觀測來探討其成因與遠震參數之關係;Scenarios of T-wave Excitation by Teleseismic Earthquakes in the Western Pacific
    Authors: 魏文宏;Wen-Hong Wei
    Contributors: 地球物理研究所
    Keywords: 海洋低速帶;聲波;SOFAR channel;acoustic wave;T-phase
    Date: 2010-08-27
    Issue Date: 2010-12-09 10:52:18 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 本研究我們使用在西太平洋海域 (Western Pacific) ,台灣島上的寬頻地震測站 (BATS station) 與日本在琉球島弧上的地震測站 (F-net Station) ,此兩者形成的地震測站陣列,其接收到來自伊豆群島 (Izu-Bonin islands) 至馬里亞納海溝 (Mariana Trench) 一系列隱沒板塊系統上的遠震事件訊號,來探討影響地震事件產生T波訊號以及地震測站接收T波訊號的控制因子。我們透過計算T波訊號的能量 (Gamma Calculation) ,來探究在接收端 (receiver-side) 控制其能量從聲波 (acoustic wave) 轉換地震波 (elastic wave) 效率的決定性因素。我們也將2005年共48個地震事件經過分析後,有17個地震事件是有T波訊號被測站接收到,特別是來自於馬里亞納海溝南端的地震事件,也有較高的機率被測站陣列所接收到其訊號,所以認為這是很好的路徑,用來觀測T波的訊號紀錄,並藉此了解其可能的傳遞模式。 此外,我們透過震源機制的分類後,發現若地震事件為正斷層 (Normal fault) 的形態時,就有極高的機率會產生T波的訊號紀錄,但之前有學者 (Dziak, 2001) 提出不同的看法,認為是走向滑移斷層 (Strike-Slip fault) 的形態,才較容易產生T波訊號。而在馬里亞納海溝的南端,其海底構造的曲度 (curvature) 相當大,也有學者 (Okal, 2001) 提出這可能是造成容易產生T波訊號的原因之一。因此綜合以上兩個因素,還需要進一步的研究,才能得知在震源端部分(Source-side)主要控制產生T波訊號的因素。 至於接收端的部分,台灣的東部海域,有極為陡峭的海底地形構造,使得T波訊號再由聲波轉換成地震波時會更有效率,以至於在台灣東部海岸線上的地震測站,只要是有產生T波訊號的地震事件,這些位在東部的測站都可以收到 T波的訊號紀錄,甚至可以往內陸約50公里的測站都可以收到到 T波的訊號紀錄。而T波波相的入射路徑與海岸線的夾角,若越接近垂直,就有較好的轉換效率,若呈現斜交的狀態,其轉換效率就較差,因此這夾角也是控制地震測站是否能收到T波訊號紀錄的重要因子之一。We used seismic station array on the margin of the Western Pacific to examine the controlling factors of earthquakes in the Izu-Bonin-Mariana subduction zone to excite T waves. The observed excited T waves in turn were used to investigate the decisive parameters for receiver-side acoustic-to-elastic conversion, in a quantitative fashion by the Gamma calculation. Having examined earthquakes in 2005, 17 out of 48 are T-excited events. We have discovered a preferential source-receiver pair for observations of T waves, namely, earthquakes in the southern Mariana Arc as recorded by stations in East Taiwan coastline. Additionally, the T-excited events correlate strongly with normal faulting type of earthquakes. While the strong curvature of the mid-SOFAR isobaths in the South Mariana Arc and the nearly perpendicular incidence to the receiver shoreline of earthquakes herein are conceptually attributed the preferential pair, the correlation with normal-faulting earthquakes needs to be cautiously examined by further studies. On the receiver side, the steeply dipping slopes of the East Taiwan coasts act as efficient interfaces for acoustic-to-elastic conversion. The converted T-waves can be recorded by stations even 50 km inland. The angles between incidence and receiving shoreline also determine the efficiency of receiver-side conversion.
    Appears in Collections:[地球物理研究所] 博碩士論文

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