Abstract:

The Zhumadian-Huaibin depression, which is located in the southern margin of the North China block, is a NW trending faulted basin between the thrust nappe belt on the northern margin of Qinling Mountains and Xiping-Pingyu uplift and controlled by the NW trending Zhumadian-Xixian Fault and Suyahu Fault. To find out the risk base of earthquake disasters and identify the characteristics of seismotectonic in Zhumadian City, based on the analysis of deep seismic exploration results, we used high-resolution shallow seismic reflection imaging technology to complete a shallow seismic profile, about 22km long, and obtain the fine near-surface structure image and fault characteristics of Zhumadian-Huaibin depression.

As regards seismic data acquisition, we used an observation system with 3m channel spacing, 15m shot spacing, 180 recording traces and 18 folds. The seismic wave is generated by a M18-612 vibrator, with a scanning frequency band of 20-160Hz and a scanning length of 12s. The data processing adopts the common center point stacking method, with a focus on improving the signal-to-noise ratio. The processing process mainly includes the elimination of waste traces, static correction, pre-stack filtering, predictive deconvolution, velocity analysis and NMO correction, residual static correction, common center point stacking, post-stack denoising, etc. The resulting shallow seismic profile has a high signal-to-noise ratio, clearly reflecting the near-surface structural changes and fault characteristics of the Zhumadian-Huaibin depression. Similar to the characteristics of deep seismic reflection profiles, the Zhumadian-Huaibin depression on the shallow seismic profile also exhibits a fault-controlled fault basin.

The shallow seismic profile reveals multiple sets of distinct stratigraphic interface reflections, which are characterized by continuous horizontal and dense vertical layering on the profile, with typical sedimentary stratigraphic reflection characteristics. Taking the bottom interface of the Neogene and Paleogene as the boundary, there are three distinct sets of reflection characteristics in the upper, middle, and lower layers, reflecting the sedimentary differences of different tectonic periods. The lateral continuity of the reflection waves in the Neogene and Quaternary strata is good, and the overall performance is a tilted layer with high west and low east, reflecting the overall subsidence of the Southern North China region since the Neogene, and forming relatively stable Neogene and Quaternary systems; The bottom interface of the Neogene and the overlying Paleogene show obvious angular unconformity, reflecting the sedimentary discontinuity between the Neogene and Paleogene formed by the overall uplift and erosion of the Southern North China region in the late Oligocene; The lateral fluctuation of reflected waves in the Paleogene strata reflects that during the Paleogene period, the southern margin of the North China block entered a stage of fault basin development with the Southern North China region, and the the Paleogene strata was controlled by tectonic movements and fault activities; Under the Paleogene bottom interface, at both ends of the profile the reflected wave energy is weak and the continuity of the same phase axis is poor, it is speculated that it is early Paleozoic sedimentary rock and Archean dense metamorphic rock mass.

The results show that the Zhumadian-Huaibin depression was formed during the development stage of the fault basin in the Southern North China Basin in the Paleogene; The Zhumadian-Xixian Fault, which controls the western boundary of the depression, is composed of four east-dipping normal faults, manifested as a set of fault step belts that fall down layer by layer from west to east, and has not staggered the bottom interface of the Neogene, is speculated to be an active fault in the late Paleogene period; The Suyahu Fault, which controls the eastern boundary of the depression, is composed of three west-dipping normal faults, and has staggered upward to the middle-upper part of the Neogene, and is speculated to be an active fault in the middle-late Neogene period.

Suyahu Fault has a significant impact on the local changes in the near-surface strata and the trend of modern rivers and lakes, it is recommended to focus on earthquake prevention and disaster reduction work in the Zhumadian City. This study provides a geophysical basis for further understanding the near-surface structural characteristics and basin-controlling fault activity of Zhumadian-Huaibin depression, which has important scientific value and social benefits for earthquake disaster mitigation and urban planning of the Zhumadian City.

Key words: Southern margin of North China block, Zhumadian-Huaibin depression, Zhumadian-Xixian Fault, Suyahu Fault, Seismic profile

摘要：

为摸清驻马店市地震灾害风险底数、 查明地震构造特征, 文中在分析深地震探测成果的基础上, 采用高分辨率浅层地震反射成像技术跨驻马店-淮滨凹陷完成了1条长约22km的浅层地震剖面, 获得了驻马店-淮滨凹陷的近地表精细结构图像和断裂特征。结果表明, 驻马店-淮滨凹陷形成于古近纪南华北盆地断陷盆地发育阶段; 控制凹陷西边界的驻马店-息县断裂由4条E倾的正断层组成, 表现为一组由西向东层层下掉的断阶带, 推测为古近纪末期活动断裂; 控制凹陷东边界的宿鸭湖断裂由3条W倾的正断层组成, 控制着现代河流的走向, 推测为新近纪中晚期活动断裂。研究结果为进一步认识驻马店-淮滨凹陷近地表构造特征和控盆断裂活动性提供了地球物理学依据, 对驻马店市的防震减灾和城市规划具有重要的科学价值和社会效益。

关键词: 华北地块南缘, 驻马店-淮滨凹陷, 驻马店-息县断裂, 宿鸭湖断裂, 地震剖面