Investigation of Fine Velocity Structure of the Basement Layer of the Shallow Crust in Western Yunnan Region

In this paper the authors have discussed the results of investigation of fine velocity structure in the basement layer of the Simao-Zhongdian DSS profile in western Yunnan region.The depth of upper Pz interface of the basement layer is about 0-3.5 km,and the depth of the lower P1 interface is 11.0-17.0 km.The velocity of the basement layer on the southern side of the Jinhe-Erhai deep fault is 5.70-6.30 km/s,and has increased to 6.30-6.50 km/s on the northern side.Their transitional zone is situated near Jianchuan County.Along the profile some localities,where the faults cut across the lateral variation of Pz interface velocity,are quite obvious in addition to the variation in depth.The velocity isopleths are relatively sparse in the southern region of JYQ S.P.(shot - point),near the DC S.P.,and in the south ZT S.P.The magma has apparently risen up along the deep faults to the upper crust in these localities,forming a large intrusive rock zone in the basement layer.In Jinggu region the basaltic magma

鄂尔多斯西缘中上地壳Pg波速度成像研究

利用鄂尔多斯西缘30个测震台站记录到的5 370次地震的24 860条Pg波射线数据,反演了该区域中上地壳Pg波速度横向变化结果,以及台站走时校正和地震事件走时校正项。结果表明:(1)鄂尔多斯西缘中上地壳Pg波速度结构呈现明显的横向不均匀性;稳定的阿拉善块体和鄂尔多斯块体主要表现为高速区,两块体边界两侧存在高速到低速的明显转换;银川盆地与吉兰泰盆地属于相对低速区,几条主要的断裂带或断裂段属于显著低速区。(2)1970年以来研究区5级以上中强地震多发生于高、低速区的转换地带,反映了地壳结构横向变化剧烈区为地震频发区。(3)台站台基及走时钟差造成的系统走时误差较小;研究区周边地震定位误差偏大、中部地震定位误差偏小,说明地震定位误差大小与台站分布密切相关。