宁夏吴忠地区北部的浅部结构和隐伏断裂——地震反射剖面结果

应用浅层地震勘探法对宁夏吴忠地区北部的浅部地壳结构和隐伏活动断裂进行研究。结果表明,该区存在2条隐伏断裂,分别为银川主断层南段和新华桥断层。推测银川主断层南段为近SN走向的W倾正断层,断层下盘地层界面一般呈近水平状展布,而在断层上盘,T_Q及其以下的地层界面向断面方向倾伏并显示出逆牵引现象,断层向上错断了第四系内部。钻孔联合地质剖面及浅层地震探测结果共同揭示新华桥断层为一条走向NE,倾向SW的正断层,深、浅地震测线控制的新华桥断层延伸长度9 km左右,向上错断了第四系内部的T_(02)界面。

Characterization of Shallow Structures and Buried Faultsin the North of Wuzhong Area, Ningxia Based on Seismic Reflection Profiles

Active faults are not only the original causes of earthquakes but are also the most serious earthquake damage experienced by areas along fault lines. Casualties in areas along fault lines are greater than those in areas on both sides of faults. Thus, active seismic fault exploration and seismic hazard assessment within urban areas are crucial. These approaches can help us understand the characteristics and hazards of active faults in specific areas and enable us to take targeted measures for earthquake prevention and disaster reduction to reduce the severity of urban earthquake disasters. In this work, shallow crustal structures and buried active faults in the northern region of Wuzhong, Ningxia were studied through the shallow seismic exploration method. Several high-resolution shallow seismic reflection lines were deployed to determine the position and depth of active faults and the extension direction, possible activity, and shallow features of buried faults. The results of this study showed that two buried faults exist in the study area:the southern part of the main Yinchuan Fault and Xinhua Bridge Fault. The southern part of the main Yinchuan Fault may be a W-trending normal fault with a nearly NS direction. The strata of the footwall of this fault show a horizontal distribution pattern. In the hanging wall of this fault, layer T_Q and the following strata are inclined toward the direction of the fracture surface, which exhibits reverse drag phenomenon. The southern part of the main Yinchuan Fault breaks up the Quaternary Interior. The drilling geological section and the result of shallow seismic exploration jointly revealed that the Xinhua Bridge Fault is a SE-trending normal fault. Deep and shallow seismic data illustrated that the Xinhua Bridge Fault extends for approximately 9 km and breaks up the T₀₂ interface in the Quaternary Interior.