摘要
用近震资料能得到在水平向和垂直向分辨率较高的地壳速度结构.计算过程中,分别进行定位和速度结构反演的运算,叠代求解.利用北京电信传输台网的资料,用ACH方法对发生在该地区的147个地震进行定位.根据P波和Pn波的走时数据,用SIRT方法反演地壳的三维速度结构.SIRT方法具有物理意义清晰、计算速度快的特点,在微机上即可实现大数据量的反演计算.数值模拟结果显示,SIRT方法的反演结果也是比较理想的.为反演京津唐地区的地壳结构,将研究区域分为三层,各层又划分为13×13个均匀块体,用147个地震的3310条P波和Pn波走时数据反演各块体的速度值.计算结果表明,在地壳上部,速度分布变化不大;中部的平原地区速度低,山区速度高;在北京和唐山之间的地壳下部则明显地存在一低速区,它和远震资料得到的上地幔低速区的位置吻合,表明地幔深部物质向上的侵入,影响了华北地区的地震活动.
The better resolution in horizontal and vertical compenents for the crustal velocity structure can be obtained by using local earthquake data. For events occurred in Beijing, Tianjin and Tangshan area, the earthquake location and velocity structure inversion were calculated iteratedly. 147 earthquakes occurred in this area were relocated with ACH algorithm by using the data from Beijing Telemetered Seismic Network. Using SIRT algorithm, the crustal 3D velocity structure was inversed from the P and Pn arrival times. The SIRT algorithm is characteristic of clear physical meaning and fast calculation. The inversion with a large amount of data can be done in PC micro - computer. The results of digital modeling show that the SIRT algorithm is desirable.In order to inverse the crustal structure of Beijing -Tianjin-Tangshan area, we divided the crust into three layers, and divided each layer into 13×13 homogeneous blocks. The velocity values of the blocks were inversed by 3310 P and Pn arrival times of 147 earthquakes. The inrersion results indicate that: (1) the velocities vary slightly in the upper crust; (2) for middle layer of the crust, the velocities are lowre in the plain and higher in the mountain area, and (3) there is a low velocity zone between Beijing and Tangshan in the lower crust. The low velocity zone in the lower crust is coincident with the position of upper mantle low velocity zone obtained by teleseismic data. It means that there have been material intrusion from deeper mantle, which affects the seismicity in North China.
出处
《华北地震科学》
北大核心
1994年第2期14-20,共7页
North China Earthquake Sciences
关键词
京津唐地区
地壳
速度结构
地震
Beijing, Tianjin and Tangshan area, SIRT algorithm, crust, 3D velocity structure inver-sion
