太行山断裂带东南缘地壳三维P波速度结构成像

应用多年地震台网观测数据,使用多震相走时成像方法获得了太行山断裂带东南缘地壳的三维P波速度结构模型。结果表明:速度结构图像在浅部较好地反映了地表地形、地质构造的特征,深部显示地壳速度具有明显的横向变化特征。12km深度以上显示研究区北部太行山隆起区地壳主要呈现为高速区,南部沉降区为低速区,而12km深度以下具有反转的特点。整体显示速度异常的走向大致与邻近活动断裂走向一致。垂直速度剖面显示研究区地壳具有分层特征,上地壳厚约10km,速度横向变化较小;中、下地壳的界面呈现局部上隆或凹陷状,横向起伏变化较大。通过分析速度、断裂与中强地震发生的关系推测研究区具备发生中强震的深部孕震条件。

Tomography of 3D P-wave Velocity Structure of Crust at Southeast Margin of Taihang Mountains Fault Zone

We present a new three-dimensional model of the crustal P-wave velocity structure of the southeastern margin of the Taihang Mountains fault zone, which we developed by inverting 14 078 arrival-time data recorded by a local seismic network from 1981 to 2012. The results provide important new insights into the deep structure environment of the research region. The tomographic images show that the velocity distribution can be used to describe the characteristics of the surface topography and geologic structure at shallow depths, while in the deeper crust, the velocity distribution exhibits obvious lateral variation characteristics. The results for depths of less than 12 km represent the northern study area where the Taihang Mountains crustal uplift is located, which is mainly characterized as a high-speed zone. However, the southern settlement area of the low-speed zone and the results for depths greater than 12 km exhibit reversed characteristics. The velocity sections reveal that the velocity anomaly is roughly in line with the direction of nearby active faults. Based on the velocity profile, we determined the crust in the study area to be layered such that it could be divided into three layers, with the upper crust having a depth of 10 km. With respect to the lateral velocity change, there is little variety in the upper crust, but great variety in the middle and lower crusts. Earthquakes are mainly distributed in the range of 4 km to 20 km depth in the crust. On the basis of our analysis of the relationship between the velocity, faults, and strong earthquakes, we speculate that our study area has the necessary preparation conditions for the occurrence of a strong earthquake.