小江断裂带北段地壳浅层P波速度各向异性观测的原理与数值试验  

Observation of P-wave velocity anisotropy of the shallow crust in the northern Xiaojiang fault zone:Principle and numerical tests

作　　者：马起杨 许力生[1] 严川[1] 李春来[1] 许康生 

机构地区：[1]中国地震局地球物理研究所,中国北京100081 [2]甘肃省地震局,中国兰州730000

出　　处：《地震学报》2016年第1期15-28,157,共14页Acta Seismologica Sinica

基　　金：中国地震局地球物理研究所基本业务费专项(DQJB14B01);国家自然基金(41474046)联合资助

摘　　要：以二维情形下观测速度场为各向同性场和各向异性场的叠加为前提,提出了一种利用走时残差估算地震波速度各向异性的方法,即剩余慢度矢量法.利用小江断裂带北段巧家流动地震台阵24个台站记录的3 181次地震事件的P波走时残差,采用剩余慢度矢量法计算了各观测台站周围水平方向上尺度为0.5°×0.5°,震源深度为0—5km的剩余慢度矢量,由此得到了P波快波和慢波方向.计算结果表明,大部分观测台站周围的P波速度方向性较为一致,快波方向为ESE向,慢波方向为NNE向.快波方向与小江断裂带北段应力场P轴方向较为一致,而慢波方向与应力场T轴方向一致,表明应力的长期作用可能是导致P波速度各向异性的重要原因.This paper proposes a new technique, residual slowness vector tech- nique （RST）, for estimating anisotropy of the seismic velocity using the resi- duals of traveling times assuming that 2-D observed velocity field is taken as the superposition of anisotropic field and isotropic one. And then the technique is applied to P traveling time residuals of 3 181 events recorded by 24 stations of the Oiaojia Array, a mobile array of seismic broadband stations installed across the northern Xiaojiang fault zone. The residual slowness vectors are calculatedwithin a scale of0.5°×0.5°in the horizontal direction and 0--5 km in the verti- cal direction around the observation stations. Finally the polarization directions of the fast P-velocity and slow P-velocity are obtained at all the stations by using the RST. The results show that the directions of the P-velocity at most of the stations are in good agreement. The fast-P directions point to ESE, which near- ly agrees with the P axis direction of stress field in northern Xiaojiang fault zone, while the slow-P directions point to NNE, which nearly agrees with the T axis direction, implying that long period of stress action might be one of the important factors causing the P wave velocity anisotropy in this region.

关 键 词：各向异性 P波速度 走时残差 小江断裂带北段 

分 类 号：P315.2[天文地球—地震学]