太原盆地及周边地区双差层析成像

山西断陷带位于鄂尔多斯与华北地块交汇处，是我国著名的历史强震活动带之一，尤其是断陷盆地中部区域，6级以上地震频发.本研究旨在揭示忻定盆地中南部、太原盆地及临汾盆地中北部交汇处的深部结构特征，分析盆地的形成和演化，探讨该区域孕震环境.利用山西地震台网观测数据以及固定地震台站融合流动台站得到的地震数据，共7455个地震事件，采用双差层析成像方法，反演得到了太原盆地及周边地区的三维P波速度结构及精定位结果.层析成像结果显示，忻定盆地、太原盆地的中上地壳为明显的低速异常，被高速的石岭关隆起隔开，深部结构特征相对简单.太原盆地、临汾盆地及灵石隆起之间的深部结构特征较为复杂，反映了两个盆地演化过程的复杂性.穿过忻定盆地的速度剖面显示，在中地壳存在明显的低速异常体，且大部分地震都发生在该低速体上方；穿过太原盆地北部的剖面显示，该区域在20~25 km深度范围内有较密集的地震分布，并勾画出交城断裂呈犁形的断层特征；穿过太原盆地中部的剖面显示，太原盆地自西向东沉积层逐渐减薄；穿过临汾盆地的剖面揭示，汾东断裂在浅部倾角较陡，随深度增加倾角逐渐变小，倾向向东.

Crustal structure beneath the Taiyuan Basin and adjacent areas revealed by double-difference tomography

The Shanxi rift system is located at the junction of the Ordos and North China blocks, where some historical major earthquakes are documented. Especially many earthquakes greater than M6 have occurred in the middle of this tectonic zone. This study aimed to reveal the velocity structures around the center and the northern part of the Linfen and Taiyuan basins and the center and the southern part of the Xinding basin, analyze the formation and evolution of these basins and discuss the seismogenic environment in this region. Using travel times of 7455 local earthquakes recorded by 30 temporary stations and 50 permanent stations, we obtained 3-D seismic velocity structures and precise earthquake locations of the Taiyuan basin and adjacent areas using the double-difference tomography method. The tomography results show that the upper and middle crust of the Xinding and Taiyuan basins has low velocity anomalies, which are separated by high velocity anomalies in the Shilingguan uplift. The deep structures of the Taiyuan basin, Linfen basin and Lingshi uplift are more complex than other regions, likely associated with the complicated evolution processes of these two basins. The velocity profile crossing the Xinding basin indicates an obvious low-velocity zone in the middle crust. Most of the earthquakes occurred above the low-velocity zone. The profile crossing the north part of the Taiyuan basin shows intensive seismicity in 20~25 km depth range and delineates the Jiaocheng fault as listric shape. The profile crossing the central part of the Taiyuan basin shows that the depth of the sedimentray layer decreases from west to east. The profile crossing the Linfen basin reveals that the Fendong fault dips to the east and the dipping angle decreases with depth.