下扬子江苏地区P_n残差与上地幔波速各向异性

本文搜集江苏台网1982年-1987年2月间发生在江苏及其邻近地区103次地震的1047个P_n数据,经过静校正和质量分类,重新计算了震中距.选择灌云台为参考台,对一次地震的P_n数据,其它台均减去参考台的数据,成功地消除了与震源参数不确定有关的误差.处理中采用质量加权,获得了上地幔平均速度、大部分台P_n残差以及不同方位上P_n视速度估计值. 按Backus给出的波速各向异性的公式,求出江苏地区P_n速度与方位之间有2％左右的速度各向异性,最大方向和对称方向近南北,最小方向为北东东.推断其成因是由于白垩纪至第三纪期间壳下岩石圈北南向流变引起橄榄石晶体从优定向的结果.这为苏北盆地及下扬子碳酸盐岩地区地质构造形成发展动力学的建立提供了有利的深部依据.

P_n-WAVE TIME RESIDUALS AND SEISMIC ANISOTROPY OF THE UPPERMOST MANTLE IN JIANGSU,LOWER YANTZE AREA

During 1982 and 1987, Pn-waves 103 of earthquakes which are located in Jiangsu and its adjacent areas were recorded by Jiangsu station network. 1047 of Pn travel times are collected. In order to diminate the effects of source errors in the data, we choose the Guanyun station for reference. All data are reduced by that of the reference station. By processing of reliabi-litive weight, the data have shown positive Pn time residuals in southern Jiangsu and negative Pn time residauls in northern Jiangshu. The apparent velocity of Pn-wave exhibits an azimu-thal dependence, and can be expressed by the following equation:The preferred interpretation call for a slight dipping （0.65° to West） plane Moho of about 2% anisotropy of subcrustal material with a nearly NS symmetrical direction of maximal velocity.The author suggests a model In which the subcrustal media flowed viscously at nearly NS direction during Cretaceous and Tertiary Periods to cause the perferred orientation of the olivine crystals. This model can explain the origin of uppermost mantle seismic anisotropy and does not conflict with the tectonics of Jiangsu of Lower Yantzc area.