| 利用地震折射和反射波资料研究银川盆地浅部结构和隐伏断裂 |
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| 引用本文： | 李燕, 刘保金, 酆少英, 姬计法, 秦晶晶, 郭新景. 2017. 利用地震折射和反射波资料研究银川盆地浅部结构和隐伏断裂. 地球物理学报, 60(8): 3096-3109, doi: 10.6038/cjg20170817 |
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| 作者姓名： | 李燕 刘保金 酆少英 姬计法 秦晶晶 郭新景 |
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| 作者单位： | 1. 中国地震局地球物理研究所, 北京 100081; 2. 中国地震局地球物理勘探中心, 郑州 450002 |
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| 基金项目： | 国家自然科学基金（91214205，41374100）和中国地震活动断层探察-南北地震带北段项目（201408023）共同资助. |
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| 摘 要： | 银川盆地是华北克拉通西部构造活动较为强烈的一个新生代断陷盆地.为了研究银川盆地的地壳浅部结构和活动断裂特征，我们利用2014年在银川盆地完成的深地震反射剖面数据，采用初至波层析成像方法得到了银川盆地高精度的基底P波速度结构和构造形态；考虑到仅根据速度结构剖面还难以确定断裂的准确位置、断层上断点埋深、断层的近地表构造组合样式等特征，研究中还采用浅层地震反射波勘探方法对银川盆地内的隐伏断裂和1739年平罗8.0级地震的地表破裂带浅部结构进行了高分辨率成像.研究结果表明：银川盆地与两侧地块的浅层P波速度结构和沉积盖层厚度差异较大，银川盆地总体呈现出明显的低速结构特征，盆地基底面起伏变化较大，基底最深处位于芦花台断裂和银川断裂之间的银川市下方，其深度约为7000~7200 m；贺兰山隆起区显示为明显的高速特征，地表出露中-古生代基岩地层，缺失新生代地层；鄂尔多斯地块西缘的浅层P波速度明显高于银川盆地，基底埋深相对较浅，推测其新生界地层厚度小于2500 m.浅层地震反射剖面揭示的地层反射界面形态和断裂的浅部构造特征非常清楚，黄河断裂、贺兰山东麓断裂、银川断裂和芦花台断裂不仅是错断盆地基底的断裂，而且还是第四纪以来的隐伏活动断裂，这些断裂的交替活动形成了"堑中堑"的盆地结构，并对银川盆地的形成、盆地内的新生代地层厚度和第四纪沉降中心具有重要的控制作用；在近地表这些断裂表现为由2~3条断层组成的"Y字形"断裂构造，且主断裂的最新活动可追踪至晚更新世末期或全新世，是构造继承性活动的结果.本文的研究结果不仅可为进一步分析银川盆地的基底结构、隐伏断裂特征和活动构造研究等提供新的地震学证据，而且还可为该区城市规划中避让活动断层提供科学依据.
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| 关 键 词： | 银川盆地 初至波成像 基底结构 地震反射剖面 地表破裂带 |
| 收稿时间： | 2016-11-04 |
| 修稿时间： | 2017-03-15 |
Exploration of shallow structure and buried faults in the Yinchuan basin using seismic refraction and reflection data |
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| LI Yan, LIU Bao-Jin, FENG Shao-Ying, JI Ji-Fa, QIN Jing-Jing, GUO Xin-Jing. 2017. Exploration of shallow structure and buried faults in the Yinchuan basin using seismic refraction and reflection data. Chinese Journal of Geophysics (in Chinese), 60(8): 3096-3109, doi: 10.6038/cjg20170817 |
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| Authors: | LI Yan LIU Bao-Jin FENG Shao-Ying JI Ji-Fa QIN Jing-Jing GUO Xin-Jing |
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| Affiliation: | 1. Institution of Geophysics, China Earthquake Administration, Beijing 100081, China; 2. Geophysical Prospecting Center, China Earthquake Administration, Zhengzhou 450002, China |
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| Abstract: | The Yinchuan basin is a Cenozoic rifted basin in the western North China Craton with relatively intense tectonic activity. In order to probe the shallow structure and the characteristics of active faults beneath this basin, we applied a first-break wave imaging method to explore the high-precision basement P-wave velocity structure of the basin, which is based on first-break wave travel-times from deep seismic reflection profile data acquired in 2014. Considering it is difficult to determine the accurate position of the fault, the upper-breakpoint depths and the near-surface tectonic patterns of faults only according to the velocity structure profile, we also employed the high-resolution shallow seismic reflection method used to image the buried faults in the basin and the shallow structure of the surface rupture zone of the 1739 Pingluo M8 earthquake. The results show that the shallow P-wave velocity structure and the sedimentary cover thickness are largely different between the Yinchuan basin and its both sides. On the whole, the Yinchuan basin shows an obvious low-velocity structure and the basement surface exhibits large fluctuations; the deepest part of the basement is below the Yinchuan city between the Luhuatai fault and the Yinchuan fault, and its depth is about 7000~7200 m. The Helan Mountains uplift zone exhibits profound high-velocity characteristics, where the Mesozoic and Paleozoic bedrocks directly expose on the ground surface while lacking Cenozoic strata. On the western margin of the Ordos block, the shallow P-wave velocity is significantly higher than that of the Yinchuan basin, and its basement depth is relatively shallower, so we infer that the thickness of the Cenozoic strata is less than 2500 m. The formation interface distribution and the shallow tectonic characteristics of the faults revealed by the shallow seismic reflection profile is very clear. The Yellow River fault, Eastern Piedmont of the Helan Mountains, Yinchuan fault and the Luhuatai fault cut through the basement of the basin, which are active since the Quaternary. The alternating activities of these faults have led to the formation of a graben-within-graben structure, which plays an important role in the formation of the Yinchuan basin and controlling the thickness of the Cenozoic strata in the basin and the Quaternary subsidence center. In the near surface, these faults show a "Y-shape" form composed of 2~3 faults, of which the latest activity of major faults can be traced to the late Pleistocene or the Holocene, as the result of tectonic inheritance activity. The results of this study can not only provide new seismological evidence for further analysis of the basement structure, the concealed fault characteristics and the active tectonics research of the Yinchuan basin, but also provide the scientific basis for city planning to avoid active faults in this area. |
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| Keywords: | Yinchuan basin First-break imaging Basement structure Seismic reflection profile Surface rupture zone |
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