Analysis of active faults based on natural earthquakes in Central north China

As an important part of the integration of Beijing-Tianjin-Hebei, it is very important to analyze the seismic activity of active structures in Central north China. There are two sets of active faults belt in the lot, and there have been devastating earthquakes, which need to grasp the level of seismic activity. Located at the boundary of the third-order tectonic unit, there are a series of faults in the area, such as the north to the east Taihang mountain front fault, the north to the east Xinhe fault and the north to the west Cixian-daming fault, which intersect and cut each other to form fault depression basin. There are different scales of NE, NNE, and NW faults, which are considered to be the birthplace of the earthquake. At the same time, more than 6 magnitude earthquake magnitude have happened in the Cixian and Xingtai. The seismogenic structure of the research shows that these earthquakes associated with deep fault activities, the source location in the deep crust velocity structure mutation. In order to determine and analyze the P-wave velocity structure characteristics and the hypocenter distribution, and the activity characteristics of the deep space of active fault belt, the natural seismic data monitored by seismic network are collected and organized, which are used to analyze the relationship between seismic wave velocity and hypocenter position. Due to the deep migration of the crustal material and the horizontal principal compressive the NEE direction stress in North China, the crustal thickness on the west side of the Taihang mountain front fault is greater than that of the east side, from 1 km to 7 km. Along the trend, the epicenter of the small earthquake is mainly distributed in the crustal thickening area on the west side of this active fault, and the epicenter of the eastern plain is less distributed. The depth of the small earthquake is concentrated in the range of 8–20 Km. Comprehensive analysis shows that the seismic p-wave velocity structure characteristics can be divided into the sedimentary cover, upper crust, the earth's crust and the lower crust structure, thickness of different location have change, the thickness of the sedimentary cover Taihang uplift zone thickness 0.1–3 km, to 5–7 km in Handan fault depression; The thickness of the crystalline basement in the Taihang mountain uplift is 3–5 km, and the Handan fault depression basin is thickened to 7–10 km. The thickness of the crust on the west side of Taihang mountain front fault is significantly greater than that on the east side. The thickness of the crust on the west side is decreased from 36–40 km on the west side to 30–35 km on the east side and about 7–10 km on the east side. Due to the near east-west tension, the zone has disengaging movement, forming the characteristics of shovel-type normal fault combination. In the earth's crust with high-speed and low-speed layer between configuration characteristics, seismic horizon of earthquake preparation 12–18 km deep in the earth's crust, characterized by low speed and high speed layer mutation position, concentrated distribution of small earthquakes, the seismogenic layer a concentration distribution in the crust velocity structure conversion section. Seismic activity is concentrated in the west end of the Cixian-daming fault and the west side of the Xinhe fault, with an average depth of 12–18 km.