茅山断裂带及邻区精细速度结构的双差层析成像研究

选取2008~2018年茅山断裂带及周边82个测震台站记录到的516个近震Pg、Sg到时数据，采用双差地震层析成像方法对茅山断裂带及邻区进行地震重定位和三维P波速度结构的联合反演，并分析溧阳历史上两次破坏性地震与速度结构的关系。结果表明，地震重定位后残差显著降低，研究区大部分地区横向分辨率可达0.2°。P波的速度结构横向差异变化比较明显，反演后的速度与初始速度模型之间的变化率基本在±10%左右。茅山断裂带两端呈现高速特征，中段表现为低速结构。溧阳震源区1974年MS5.5地震发生在深变质岩系内的低速层上，而1979年MS6.0地震发生在深变质岩系与浅变质岩系边界上，这两次地震的发震原因可能与具有塑性流变特性的低速体和速度梯度较大的转换复合位置容易产生应力集中有关。

Fine Velocity Structure of the Maoshan Fault Zone and Adjacent Areas Revealed by Double-Difference Tomography

Using 516 local earthquake events recorded by 82 permanent stations from 2008 to 2018, we apply the double-difference tomography method to relocate seismic events and invert the 3-D seismic velocity structure of Maoshan fault zone and adjacent areas. We analyze the relationship between two destructive earthquakes and velocity structure. The tomography results show that the residual of seismic relocation is significantly reduced and horizontal resolution in most study areas can reach 0.2°. The P wave velocity structure has significant heterogeneities. The rate of change between the speed after the inversion and the initial velocity model is about ±10%. The Maoshan fault zone exhibits high velocity features at both ends, and the middle section exhibits low velocity structures. The 1974 MS5.5 earthquake occurred in the low velocity of deep metamorphic rocks in the Liyang earthquake source area, while the 1979 MS6.0 earthquake occurred on the boundary between the deep metamorphic and shallow metamorphic rocks. The reason for the two earthquakes may be that the stresses easily accumulate in the low velocity body and the boundaries with large velocity gradients.