鄂尔多斯西缘中上地壳Pg波速度成像研究*

(1.宁夏回族自治区地震局,宁夏 银川 750001; 2.甘肃省地震局,甘肃 兰州 730000; 3.四川省地震局,四川 成都 610041; 4.中国地震局地球物理勘探中心,河南 郑州 450002)

鄂尔多斯西缘; 中上地壳; Pg波速度结构; 中强地震

Mid-upper Crustal Velocity Tomography of Pg Wave in Western Margin of Ordos
ZENG Xianwei1,FENG Jiangang2,LONG Feng3,XIN Hailiang4

(1. Earthquake Administration of Ningxia Hui Autonomous Region,Yinchuan 750001,Ningxia,China)(2. Earthquake Administration of Gansu Province,Lanzhou 730000,Gansu,China)(3. Earthquake Administration of Sichuan Province,Chengdu 610041,Sichuan,China)(4. Geophysical Exploration Center,Zhengzhou 450002,Henan,China)

western margin of Ordos; mid-upper crust; velocity structure of Pg wave; moderate-strong earthquake

备注

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。

In the paper,we obtained the inversion result of mid-upper crustal velocity tomography of Pg wave,station term perturbations and event term perturbations in western margin of Ordos,using 24 860 Pg wave rays of 5 370 earthquakes recorded by 30 seismic stations in the region. The results show that:(1)The mid-upper crustal velocity structure of Pg wave presents obvious lateral inhomogeneity. The stable Alashan block and Ordos block are mainly high speed regions,and there exist obvious high speed to low speed conversion on both border sides of the two blocks. The Yinchuan basin and Jilantai basin belong to relatively low velocity zone,and several major fault or fault segments belong to significant low velocity zone.(2)Since 1970,M≥5 moderate-strong earthquakes in the region mainly occurred in the high speed to low speed conversion zone. Therefore,the region where lateral velocity structure changes fiercely is that where earthquakes occur frequently.(3)In addition,the system travel time error caused by station base and clock correction is small. And,location error of earthquakes occurring in the surrounding region is larger than that occurring in the central region. It illustrates that the size of earthquake location error is closely related to the seismic station distribution.