【作者】 石玉涛；

【导师】 高原；

【作者基本信息】 中国地震局地震预测研究所 ， 固体地球物理， 2006， 硕士

【摘要】 地壳岩石中广泛存在着直立的定向排列的平行裂隙,即EDA(大范围扩容各向异性)微裂隙,这是产生地壳(至少是上地壳)介质各向异性的主要原因。剪切波在这样的各向异性介质中传播会发生分裂现象。快剪切波的偏振方向与裂隙的走向一致,即快剪切波偏振方向反映了原地最大主压应力方向;慢剪切波的时间延迟反映了介质的各向异性程度,这与裂隙结构、裂隙间流体有关。对于这种含流体EDA裂隙结构,可用APE(各向异性孔隙弹性)理论进行其动态变化特性的研究。云南地区位于青藏高原东缘,地区内有许多大的断裂带纵横交错,地质构造十分复杂,地震活动强烈,地震主要沿NE、NW和NS三组地震带分布。该地区的主应力轴方向为NNW,由西藏东部的岩壳向东南的推挤造成。2000年以来,云南地区多次发生震级5.0以上的地震,为开展云南地区地壳介质各向异性研究提供的背景资料,有利于进行剪切波分裂时间变化的分析研究。本研究利用云南省遥测数字地震台网近场资料进行了剪切波分裂的研究,使用近几百条剪切波窗口内有效记录,采用SAM分析方法分析云南地区地壳介质的各向异性。云南地区地质构造复杂,震区同时存在多条规模不等运动方式不一的断裂及断裂交汇,通过对各台站的各向异性的分折,得到总体上快剪切波偏振方向主要在NW、NNW或近N-S方向,与区域主压应力方向基本一致,个别台站的快剪切波偏振优势取向存在差异。研究得到,各台站慢剪切波时间延迟的平均值在1.0-7.3ms/km范围内,平均值为2.78ms/km。研究表明,位于活动断裂上的台站的快剪切波偏振优势方向,与活动断裂的走向、GPS主压应变方向以及主压应力方向一致。离开活动断裂的台站,由于区域应力场的作用,快剪切波偏振优势方向与主压应力方向和GPS主压应变方向一致。复杂的局部构造会控制或影响台站的快剪切波偏振优势方向,造成与主要活动断裂走向不一致,或与相邻台站的结果相差较大的现象。复杂的地质结构也会造成快剪切波偏振较为离散或出现多个优势方向的现象。云南地区的快剪切波偏振特性的研究表明,根据快剪切波偏振优势方向的分布可以判断地下断层是否为活动断层。根据对地质背景和地震活动的研究和认识,在没有精确深度定位数据的情况下,可以适当增加震中距比较小的地震事件波形作为数据补充。这种扩展数据技术,在更多还原

【Abstract】 Parallel vertical cracks widely exist in the lithosphere (EDA cracks) and result in shear wave splitting in the earth’s curst, at least in the upper lithosphere. Splitting will occur while shear wave transmits in anisotropy media. The polarization of fast shear-wave is consistent with the crack’s direction, which means that the polarization of fast shear-wave reflects the direction of the principal compressive stress. The time delay of slow shear wave reflects the extent of anisotropic media. To the structure with EDA cracks and liquid, APE theory can be used to explain its dynamic change.Yunnan region is located at eastern edge of Tibetan plateau. There are many big intersected rupture zones with strong seismic activities. The geological structures in the area are very complex, which mainly distribute along NE、NW and NS direction. The direction of compressive stress axis is NNW, caused by rock curst in eastern part crushed to the south-eastern. Since 2000, many earthquakes with Ms≥5.0 occurred for several times, thus there are many data which can be used for analysis of shear wave splitting. This paper shows the research of shear wave splitting by applying near field data from regional telemetry seismic network in Yunnan region. There are several hundred efficient records within shear wave window, and SAM method is selected as the main tool to analyze crustal anisotropy in Yunnan region. Because of the fact that the geological structure is complicated in Yunnan region, the polarizations are complicated.Generally, polarizations of fast shear-wave are mainly in NW, NNW and NW direction, which are almost consistent with regional principal compressive stress. Results show that the range of time-delay is from 1.0 to 7.3 ms/km, average value is 2.78 ms/km. Fast shear-wave polarizations of the stations which locate in active ruptures are更多还原