A Study On The Fine Crustal Structure Of Huixian-Fengqiu Profile In The Southern Margin Of Taihang Mountains By Seismic Reflection Data

The deep seismic reflection method based on multiple coverage techniques has unique advantages in detecting the fine structure and tectonics of the crust and upper-mantle.It is an effective way for exploration of energy and mineral resources,research on seismogenic structural features,relationships between deep and shallow structures.The southern margin of Taihang Mountains is located in the transitional belt between the Taihang Mountains and the North China Plain,where is the intersection of the Taihang Mountain piedmont fault zone and the Xinxiang-Shangqiu fault.In this area,the neotectonic movement is strong and the active faults are developed.It is one of the major earthquake surveillance and defense areas in China.Therefore,the deep seismic reflection method is used to detect the fine structure of the crust and the structural relations between the deep and shallow faults in the southern margin of Taihang Mountains.The research results not only have scientific significance for deep understanding of the complex geological structure characteristics,seismogenic tectonic setting and active fault research in the area,but also provide scientific basis for earthquake prevention and disaster reduction planning and major lifeline construction in this area.In this dissertation,we used the Huixian-Fengqiu deep seismic reflection profile and shallow seismic exploration data completed by the Geophysical Exploration Center of the China Earthquake Administration to dissect the underground structure in the southern margin of Taihang Mountains,and obtained the fine structure images in the crust depth range.The results of the study indicate that the crust structure in this area has obvious characteristic of vertical stratification and horizontal block.The thickness of the crust is 33 to 39 km,and the Moho surface gradually deepens from east to west.The structure of the upper crust in the southern margin of Taihang Mountains is complex and the active faults are developed.The tangyin graben and uplifts on both sides show a typical basin and range structure on the section,and its boundaries are obviously controlled by shovel-shaped normal faults.The deep fault of the crust is located on the east side of the Tangyin graben,which faulted the lower crust and the Moho surface.This is a deep structure that must be paid attention to in the seismic risk assessment of the area.In order to study the shallow structure and structural features of the area,we used a tomography method of first-arrival travel-time acquired from deep seismic reflection profile to explore the shallow P-wave velocity structure of the southern margin of Taihang Mountains.The results indicate a good corresponding relationship among the variations in P-wave velocity,the thickness of sedimentary cover and the position of the faults.In order to probe the near-surface features of active faults in the research area,two shallow seismic reflection profiles crossing the buried faults were carried out.The results show that Tangxi fault is a normal fault plunging towards east,controlling the western boundary of the Tangyin graben.It's an active fault during the middle Pleistocene.Tangdong fault is a west dipping fault,and it's the main controlling boundary fault of the Tangyin graben.The latest activities can be traced to the early period of late Pleistocene.The results of this study can provide new seismological evidence for further analysis of the basement structure and the concealed fault characteristics of the southern margin of Taihang Mountains.