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

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