宁夏地区上地幔地震各向异性特征

Seismic anisotropy of the upper mantle in Ningxia region

利用宁夏6个三分向宽频带数字地震台记录的震中距在85°—110°,震级大于6级的远震SKS波震相作了偏振分析,采用Silver-Chan方法求得了分裂参数,获得了宁夏地区上地幔各向异性图像.结果表明,宁夏地区上地幔各向异性普遍存在,本区盐池台(YCI)所在的鄂尔多斯块体下方的各向异性可归结为"化石"各向异性,其它地区的各向异性特征则反映了正在进行的构造运动,由此可为贺兰山脉东西两侧复杂的运动图像提供深部证据.最后推测本区的青藏高原东北缘—阿拉善块体及银川断陷区壳、幔的运动是耦合的,而鄂尔多斯块体地区壳、幔的运动型式尚不明朗.

A polarization analysis has been carried out on teleseismic SKS phases with epicentral distance between 85°and 110°and from M≥6.0 earthquakes recorded by 6 digital broadband seismic stations with 3 components in Ningxia region,China. The splitting parameters have been obtained by using the Silver-Chan method and the anisotropy feature of the upper mantle in Ningxia region has been obtained. The result shows that in Ningxia region there widely exists the upper mantle anisotropy.The anisotropy beneath the Erdos block,where the YCI station is located,could be classified as ＂fossil＂ anisotropy,while the anisotropy in other regions reflects tectonic movement undergoing,having also provided the deep evidence about the complex kinetic figure of the Helanshan Mountain and its double sides. Finally,it is inferred that in this region the movement between the crust and upper mantle from the northeast edge of the Qingzang Plateau to the Alashan Block and the Yinchuan broken region is coupled,and the Erdos Block region has not been clear yet.