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研究生:蔡敬康
研究生(外文):Jing-Kang Chua
論文名稱:研究2006至2007年臺灣區域60個Mw > 3.3的地震造成的T波之傳播路徑、振幅大小和轉換效率
論文名稱(外文):T-waves Excited by 60 Mw > 3.3 Earthquakes in Taiwan Region During 2006-2007: Implications of Their Ray Paths, Amplitudes, and Conversion Efficiency
指導教授:龔源成
指導教授(外文):Yuen-Cheng Gung
口試委員:陳勁吾
口試委員(外文):Chin-Wu Chen
口試日期:2014-05-26
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:地質科學研究所
學門:自然科學學門
學類:地球科學學類
論文種類:學術論文
論文出版年:2014
畢業學年度:102
語文別:英文
論文頁數:34
中文關鍵詞:T波T-波相臺灣海底地震儀聲速波
外文關鍵詞:T-waveT-phaseTaiwanocean bottom seismometeracoustic waves
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T波是一種地震波相,其傳播路徑至少部份會經由水體介質傳播。這種聲速波可以傳至很遙遠的距離,因此更小規模的地震也能被偵測得到。但是目前對於控制T波的振幅和到時都還不甚了解。此研究希望能夠更了解T波經由固體地殼介質進入流體海洋介質的轉換點和在海洋中的傳播路徑。我們用了一顆海底地震儀和一個位於蘭嶼的陸域地震儀,在這兩顆地震儀共同的佈站時間記錄到了60個臺灣區域規模大於3.3的地震。其中這60個地震都有被海底地震儀接收到,另外只有大約90%的地震事件被蘭嶼的地震儀記錄到。我們利用這些被臺灣地震網精確定位的地震,去計算理論走時和理論S波-T波,P波-T波的振幅轉換,結合了理論走時和理論振幅轉換,我們可以去模擬T波的振幅。模擬的T波波形與實際上觀測到的波形相符。從理論的到時,地震波的固體彈性波轉成流體聲速波的確與臺灣東部海域的海底地形有關,且我們觀察到部份T波波形缺口與地形的轉換缺口相吻合。最後我們也提出了一個全新的方法,利用地動訊號和海水壓力變化的比值,可去分辨海底地震儀接收到的T波是從海洋傳播抵達或是經由測站底下的地殼抵達。

T-waves are seismic energies that have at least partially propagated through a water body. Such waves can propagate long distances, thus are useful for studying small events at far distances. However, factors controlling the amplitude and duration of T-waves are still not clear. It is also advantageous if we know where the energy enters into the water column and which parts of the T-wave is arriving from the crust or from the water column near the receiver side. Here, we used data from one broadband ocean bottom seismometer (OBS) that recorded T-waves from 60 Mw > 3.3 Taiwan earthquakes. T-waves from 90% of these events were also recorded by an island seismic station. For these earthquakes that are well-located by a dense land seismic network, we forward-calculated the travel times of the different parts of P- and S-wave convert to T-wave, and correlated them with different paths from the earthquakes. The duration of the observed T-wave fits with the paths from available conversion points in the regional bathymetry, and the waveform gap consistent to the gap of bathymetry contour. However, arrival times of a few abyssal earthquakes show that parts of the T-waves are converted directed from the deep seafloor near the sources. We have calculated the synthetic ground motions at the conversion points along the 1000 m bathymetric contour lines. We then calculated the synthetic T-wave amplitude at those conversion points. Using such results we calculated the T-wave amplitude envelopes and found that they can fit with the observed OBS data. Furthermore, we have used the ratio of ground motions to water pressure change to determine if the T-wave is arriving to the OBS as ground motions or as acoustic waves from the water column. Such method can help us to determine the different paths and amplitudes of the T-waves recorded by the OBSs.

口試委員會審定書 i
誌謝 ii
摘要 iii
Abstract iv
Table of Contents vi
List of Figures vii
List of Tables viii
Chapter 1 Introduction 1
Chapter 2 Seismicity and Bathymetry of Taiwan Region 5
Chapter 3 Data Analyses 6
Chapter 4 Discussion 27
Chapter 5 Conclusions 31
Reference 33
Appendix Figures (DVD)

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