| 摘要: | 岩石圈非均向性的研究可以助於了解該區域的地體動力過程。因此本研究利用遠震SKS及SKKS剪力波分離的方法來探討中國大陸東南方-福建地區的地體動力機制。本研究針對福建沿海地區17個以及山區19個南北向排列的寬頻地震測站進行地震資料處理，其資料時間段分別為2008年8月至2010年6月以及2011年5月至2012年9月，而在資料處理時先以Direct Solution Method（DSM）模擬遠震地震波，再與實際地震波互相比對相對應的波相（SKS，SKKS），作為波形資料品質的篩選，最後將篩選出來的波形資料分別以：（1）波形交互對比法（Waveform Cross-correlation Method, RC），及（2）橫向分量最小能量法（Transverse Minimization Method, SC）兩種方法計算出分離參數解。
研究結果顯示，福建地區36個測站中，最後有24個測站（沿海10個和山區14個）有觀察到明顯的SKKS剪力波分離現象，並且得到分離參數解（splitting parameters），由各測站所得的快波極化方向（fast polarization, ϕf），將福建地區以25.7∘N和閩江斷裂帶為界分成三個部分，25.7∘N以南的南部地區，其快波極化方向為E-W，介於25.7∘N與閩江斷裂帶之間的中部地區，其測站主要位於斷裂帶上，且快波極化方向主要平行於斷層走向，閩江斷裂帶以北的北部地區，其快波極化方向主要分為兩個方向，分別為NNW-SSE和NEE-SWW。而快慢波分離時間（splitting time, δt）總平均約為1.32秒，最大可達2.44秒，從測站位置分布觀察到，沿海測站得到的δt大於山區測站，而在北、中、南三個區域的δt來看，北部地區是最小的，其次是中部地區，最大的是南部地區，顯示出福建地區的非均向性厚度或強度由西向東增加以及從北向南遞增的趨勢。將南部地區快波極化方向的結果與全球P波速度構造交互比對，推測其方向受到板塊之間的交互作用造成地函流流場的變化所影響。
;Seismic anisotropy of lithosphere can provide key information for understanding the geodynamic process in the Fujian region, southeastern China. In this study, we use teleseismic SKS/SKKS splitting measurements, as a tool for investigating seismic anisotropy. We selected 36 seismic stations in the Fujian to obtain two splitting parameters, fast direction and splitting time. In order to ensure the data quality, we used the Direct Solution Method (DSM) to compute synthetic seismograms based on global 1D model to check with observed seismic waveforms.Two methods, transverse minimization and Waveform Cross-correlation methods, were applied to obtain the splitting parameters for testing the reliability of the results.
Totally, there are 86 splitting measurements for 24 stations obtained in this study and can be approximately divided into three patterns from south to north. In the southern Fujian, the predominant polarizations in the south of N25.7∘show E-W direction. In the central Fujian, the predominant polarizations are in NNE-SSE direction, which are parallel to the strikes of the faults. In the northern Fujian, the predominant polarizations in the north of the Min River fault are in the NEE-SWW and NNW-SSE directions. The average splitting time of teleseismic shear waves observed from 24 stations is 1.32 s and the maximum is 2.44 s. In general, the average splitting time delay beneath Fujian coastline is greater than mountain area. The spatial distribution of time delays increases from northern part to southern part. As a result, the thickness of anisotropic layer increases from northeast to southwest in the Fujian area and in the southern part, compared with the global tomography, it can be explained that the variations of fast-polarizations could relate to the EW mantle flow created by NS collision between the India and Eurasian Plates. |
