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
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摘要
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。
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 T_(02) interface in the Quaternary Interior.
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 T_(02) interface in the Quaternary Interior.
引文
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[13] 酆少英,龙长兴,高锐,等.高分辨折射和浅层反射地震方法在活断层探测中的联合应用[J].地震学报,2010,32(6):718-724.FENG Shaoying,LONG Changxing,GAO Rui,et al.Joint Application of High-resolution Refraction and Shallow Reflection Seismic Exploration Approach to Active Fault Survey[J].Acta Seismologica Sinica,2010,32(6):718-724.
[14] 谭雅丽,王志铄,杨卓欣,等.太康MS4.7地震目标区浅层结构探测[J].大地测量与地球动力学,2017,37(10):1020-1037.TAN Yali,WANG Zhishuo,YANG Zhuoxin,et al.Shallow Structure Exploration of the MS4.7 Earthquake Target Area in Taikang[J].Journal of Geodesy and Geodynamics,2017,37(10):1020-1037.
[15] 刘保金,张先康,陈颙,等.三河—平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面[J].地球物理学报,2011,54(5):1251-1259.LIU Baojin,ZHANG Xiankang,CHEN Yong,et al.Research on Crustal Structure and Active Fault in the Sanhe—Pinggu Earthquake (M8.0) Zone Based on Single-fold Deep Seismic Reflection and Shallow Seismic Reflection Profiling[J].Chinese Journal of Geophysics,2011,54(5):1251-1259.
[2] SCHOLZ H C.The Mechanics of Earthquakes and Faulting[M].Cambridge:Cambridge University Press,1990:73-96.
[3] CRONE A J,HAILER K M.Segmentation and Seismic Behaviour of Basin and Range Normal Faults:Examples from East Central Idaho and Southwestern Montana,USA[J].Journal of Structural Geology,1991,13(2):151-164.
[4] 徐锡伟.活动断层、地震灾害与减灾对策问题[J].震灾防御技术,2006,1(1):7-14.XU Xiwei.Active Faults,Associated Earthquake Disaster Distribution and Policy for Disaster Reduction[J].Technology for Earthquake Disaster Prevention,2006,1(1):7-14.
[5] 徐锡伟,闻学泽,叶建青,等.汶川8.0级地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.XU Xiwei,WEN Xueze,YE Jianqing,et al.The MS8.0 Wenchuan Earthquake Surface Ruptures and Its Seismogenic Structure[J].Seismology and Geology,2008,30(3):597-629.
[6] 赵卫明,金延龙,刘秀景,等.吴忠、灵武地区地壳中上部速度结构[J].内陆地震,1998,12(3):256-262.ZHAO Weiming,JIN Yanlong,LIU Xiujing,et al.The Velocity Structure of The Upper and Middle Crust in The Wuzhong—Lingwu Region[J].Inland Earthquake,1998,12(3):256-262.
[7] 马禾青,任雪梅,金春华,等.2003—2004年吴忠、灵武地区地震活动性分析[J].地震研究,2006,29(2):114-117.MA Heqing,REN Xuemei,JIN Chunhua,et al.2003—2004 Seismicity Analysis of the Wuzhong and Lingwu Regions[J].Journal of Seismological Research,2006,29(2):114-117.
[8] 李惠智.对银川台记录到的灵武、吴忠地区地震资料方位异常的探讨[J].内陆地震,2000,14(2):137-141.LI Huizhi.Discussion on The Earthquake Azimuth Anomalies in Lingwu—Wuzhong Recorded by Yinchuan Station[J].Inland Earthquake,2000,14(2):137-141.
[9] 雷芳,陈玉华,董治平,等.银川地堑地震背景与近期地震活动趋势初步分析[J].高原地震,1997,9(4):58-64.LEI Fang,CHEN Yuhua,DONG Zhiping,et al.Preliminary Analysis on Seismological Background and Recent Seismicity Trend of Yinchuan Graben[J].Earthquake Research in Plateau,1997,9(4):58-64.
[10] 吕世民.宁夏吴忠市红寺堡区地质灾害综合评价研究[D].西安:长安大学,2016.Lü Shimin.Comprehensive Evaluation on Geological Disaster of Hongsibu,Wuzhong Town,Ningxia Province[D].Xi'an:Chang'an University,2016.
[11] 刘保金,何宏林,石金虎,等.太行山东缘汤阴地堑地壳结构和活动断裂探测[J].地球物理学报,2012,55(10):3266-3276.LIU Baojin,HE Honglin,SHI Jinhu,et al.Crustal Structure and Active Faults of the Tangyin Graben in the Eastern Margin of Taihang Mountain[J].Chinese Journal of Geophysics,2012,55(10):3266-3276.
[12] 刘保金,张先康,方盛明,等.城市活断层探测的高分辨率浅层地震数据采集技术[J].地震地质,2002,24(4):524-532.LIU Baojin,ZHANG Xiankang,FANG Shengming,et al.Acquisition Technique of High-resolution Shallow Seismic Data for Surveying of Urban Active Faults[J].Seismology and Geology,2012,24(4):524-532.
[13] 酆少英,龙长兴,高锐,等.高分辨折射和浅层反射地震方法在活断层探测中的联合应用[J].地震学报,2010,32(6):718-724.FENG Shaoying,LONG Changxing,GAO Rui,et al.Joint Application of High-resolution Refraction and Shallow Reflection Seismic Exploration Approach to Active Fault Survey[J].Acta Seismologica Sinica,2010,32(6):718-724.
[14] 谭雅丽,王志铄,杨卓欣,等.太康MS4.7地震目标区浅层结构探测[J].大地测量与地球动力学,2017,37(10):1020-1037.TAN Yali,WANG Zhishuo,YANG Zhuoxin,et al.Shallow Structure Exploration of the MS4.7 Earthquake Target Area in Taikang[J].Journal of Geodesy and Geodynamics,2017,37(10):1020-1037.
[15] 刘保金,张先康,陈颙,等.三河—平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面[J].地球物理学报,2011,54(5):1251-1259.LIU Baojin,ZHANG Xiankang,CHEN Yong,et al.Research on Crustal Structure and Active Fault in the Sanhe—Pinggu Earthquake (M8.0) Zone Based on Single-fold Deep Seismic Reflection and Shallow Seismic Reflection Profiling[J].Chinese Journal of Geophysics,2011,54(5):1251-1259.