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研究生:Vanisa Syahra
研究生(外文):Vanisa Syahra
論文名稱(外文):Seismic Anisotropy of the Upper- and Lower-Crust in the South Aegean Inferred from Shear-Wave Splitting
指導教授(外文):K.I. Konstantinou
外文關鍵詞:Shear-Wave SplittingCrustal AnisotropySouth AegeanMFAST
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隱沒帶是非均向性研究的有趣目標,因為隱沒帶的構造複雜性隨深度變化,並可能產生不同種類的非均向性方向。南愛琴地區是由於非洲岩石圈沿希臘海溝在愛琴海板塊下方隱沒而形成的。為了確定南愛琴地區的地殼非均向性,我們使用了EGELADOS臨時地震網絡的65個地震測站在2005年11月至2007年1月期間記錄的5193次地殼地震來測量了剪力波分離參數(快S波極化方向和時間差)。我們使用了多重濾波器自動分裂技術(MFAST),它是一種自動剪切波分裂技術,可以快速處理數千個事件。在這項研究中,我們使用了A級和B級分裂測量(δt≤0.3 s),總共獲得了3732項高質量測量。整體來說,南愛琴地區大多數站點的快速發展趨勢是北北東-南南西向。對深度變化的分析可看出,在7 – 20 km深度處,非均向性的百分比最多佔地殼非均向性的5%,平均時間差為0.149 s(±0.02 s)。少數位於沿著伯羅奔尼撒南部至喀帕蘇斯島的幾個測站,以應力誘發的非均向性為主要機制,可看出此區域並不受應力場控制。但是,我們觀察到的地殼非均向性與沿伯羅奔尼撒至喀爾巴索的活動斷層走向,以及在基克拉澤斯變質岩心複合體(MCC)掘出過程中延展流動的伸展線和大型穹頂的葉理面一致。因此也可看出,這些地區的主導機制主要受結構控制影響。 我們還將觀測到的地殼非均向性與地幔SKS非均向性進行了比較。我們的快速剪力波方向與SKS分裂測量結果基本一致,表明地殼正在與地幔發生連貫變形。
Subduction zones are interesting targets for anisotropy studies due to their tectonic complexity which varies in depth and might produce different kinds of anisotropy directions. South Aegean was formed as a result of the African lithosphere subducting underneath the Aegean plate along the Hellenic trench. Intending to determine the crustal anisotropy in the South Aegean, we measured shear-wave splitting parameters (fast shear-wave direction and delay time) using 5193 crustal earthquakes recorded by 65 seismic stations of the EGELADOS temporary seismic network during November 2005 – January 2007. We used the Multiple Filter Automatic Splitting Technique (MFAST), the automatic shear-wave splitting that allows the quick processing of thousands of events. In this study, we used A- and B-grade splitting measurements (with δt ≤ 0.3 s), and in total 3732 high-quality measurements were obtained. In general, the fast direction in most of the stations in south Aegean is trending NNE-SSW. Analysis of depth variations shows that the percentage of anisotropy at the depth of 7 – 20 km contributes up to 5% of crustal anisotropy with average delay time of 0.149 s (±0.02 s). Stress-induced anisotropy is dominating mechanism of crustal anisotropy only in few stations along South Peloponnese to Karpathos, suggesting that the regional stress field does not control the area. However, our observed crustal anisotropy is more in agreement with the strike of active faults along Peloponnese to Karpathos, and with the stretching lineation of ductile flow and the foliations of migmatitic dome during the exhumation of metamorphic core complexes (MCC) in the Cyclades. This agreement suggests that the dominating mechanism in these areas is mainly controlled by the structure. We also compared our observed crustal anisotropy with the mantle SKS anisotropy. Our fast shear-wave directions are in general agreement with the SKS splitting measurements, suggesting that the crust is deforming coherently with the mantle.
1.1. Tectonic Setting of the South Aegean 1
1.2. Previous works on stress field in the South Aegean area 3
1.3. Aims and structure of this thesis 3
2.1. The EGELADOS seismic network 7
2.2. Data pre-processing 7
3.1. Shear-Wave Splitting 12
3.1.1. Methods: MFAST package 12
3.1.2. Measurement criteria 13
3.2. Map of the crustal anisotropy 15
4.1. Depth distribution of anisotropy 24
4.2. Possible causes of crustal anisotropy 25
4.2.1. Stress-induced anisotropy 25
4.2.2. Structural anisotropy 26
4.3. Comparison between crustal anisotropy and mantle anisotropy 27
4.4. Conclusions 28
Appendix A 43
Appendix B 45
Appendix C 49
Appendix D 51
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