From March 8^th to 29^th, 1966, five earthquakes(M≥6)occurred in the Xingtai area, with the M_S6.8 earthquake on March 8^th and the M_S7.2 earthquake on March 22^nd being the most severely damaged. The Xingtai earthquake resulted in over 8 000 deaths and the economic losses up to 1 billion yuan. The Xingtai earthquake has opened the scientific practice of earthquake prediction in China and is a milestone in the development of earthquake science in China.

Based on previous research results, there is a deep fault beneath the Xingtai earthquake area, which is the energy source of earthquakes, while there is a relatively independent fault system in the shallow part, which is generally recognized by scholars. However, the divergence regarding the seismogenic structure of the Xingtai earthquake mainly focuses on the unclear coupling relationship between the deep and shallow structural systems in the seismic area. The structural relationship between deep seismic faults and the shallow Xinhe Fault system requires new evidence to determine. In addition, previous scholars have proposed the viewpoint of “Newly generated Fault”, which can better explain the rupture characteristics of the Xingtai earthquake, but it still needs to be supported by the inversion results of the seismic rupture process based on the three-dimensional crustal fine structure. There are many small earthquakes in the Xingtai area. Deep structural information can be obtained using small earthquake data. Especially after 2009, the significant improvement in earthquake positioning accuracy in North China has made it possible to obtain new insights into deep structures. By locating small earthquakes, the spatial distribution and motion characteristics of faults are characterized, and seismic travel time tomography reveals the deep crustal velocity structure characteristics of the earthquake area. Combining previous geophysical exploration results, conducting deep and shallow structural analysis is of great significance for studying the spatial distribution, motion characteristics, and coupling relationship between deep and shallow structural systems of the fault system in the study area. The continuous aftershocks after the 1966 M_S7.2 earthquake in Xingtai, Hebei Province, have provided favorable conditions for conducting studies on deep tectonic structures in the region.

In this paper, based on the observation data of the Hebei seismostation from 1991 to 2021, we obtained the precise position results of 9 644 earthquakes in Xingtai and its neighboring area using the double-difference positioning method, and depicted the spatial patterns of deep ruptures. Based on the observation data of the North China Mobile Seismic Array from 2006 to 2008, 38 578 P-wave arrivals were used to obtain high-resolution travel time tomography results in the study area. This study shows that there are strong lateral heterogeneities in the velocity structure of the crust in the study area, with obvious low-velocity anomalies in the upper crust and high-velocity anomalies in the middle and lower crusts between the Xinhe Fault and the Yuanshi Fault, and the Xingtai earthquake is located at the junction of the high- and low-velocity anomalies, which has the medium conditions for accumulating large amounts of strain energy and is prone to rupture and stress release. The general trend of the dense zone of small earthquakes in the Xingtai earthquake area is relatively consistent with that of the eastern boundary of the high- and low-velocity anomalies. It is assumed that the deep and shallow fractures spreading along the eastern boundary of the high- and low-velocity bodies have been connected up and down and that the boundary of the anomalies is also a part where velocity changes are relatively strong and easily lead to seismic rupture; the results of various seismic and geological surveys have revealed that a deep major rupture that cuts through the entire crust exists beneath the Xingtai earthquake zone, with SE tendency and the upper breakpoint located near Dongwang, and the Xingtai earthquake prompted the deep and shallow pre-existing ruptures to connect from top to bottom.

Based on ANSYS parallel software platform, and according to active tectonic block region division and distribution of active faults in North China, and combined with GPS data, the range of the numerical model is defined as 99.8°～121.4°E, 27.9°～42.3°N, which contains a majority of the North China active tectonic block region and parts of other block regions including the Tibetan plateau, the Xiyu, South China, and the Northeastern Asia. The model is divided into 416582 elements whose average side length is 25km with 582392 nodes. The main research results are: (1)Simulation of crustal movement velocity and analysis. The results show that the velocity of crustal movement in North China as a whole decreases from east to west and increases from north to south. It is an almost match between simulation results and GPS observed velocity field. (2)Simulation of the slip of faults and analysis. Considering all known late Quaternary active faults in North China in the model and according to the simulation results, the slip of faults obtained from simulation and that from geological survey are almost consistent. (3)Simulation of strain fields and analysis. By numerical simulation, the minimum strain and the maximum principal strain in North China in 1999-2004 and 2004-2007 are calculated. The horizontal strain direction in North China is in accord with the strain direction obtained from inversion of focal mechanism solutions, GPS observations, etc. by previous studies.

Earthquake preparation and occurrence is a complex physical process.Although the earthquake abnormalities are varied,the strain energy accumulation is requisite before an earthquake.Earthquake prediction analysis must consider the strain energy accumulation process.As hard to go into the Earth's interior,direct measurement of stress and strain in deep focus is very difficulty.The use of numerical analysis,which constructs three-dimensional dynamic models of the crust and upper mantle to simulate the rock deformation process,is currently one of the most effective methods to study the crustal energy transfer and accumulation.The simulation result of current crustal deformation is consistent with the existing GPS data around the Eastern Himalayan Syntaxis and its surrounding areas,in that the crustal horizontal displacement field of the eastern Tibetan Plateau rotates clockwise around the Eastern Himalayan Syntaxis.Current effective stress concentration areas mainly distribute along the block boundary fault belts around the Eastern Himalayan Syntaxis,especially along the southeast section of Jiali Fault,Moto Fault,Apalong Fault,India-Myanmar subduction zone and the Sichuan-Yunnan border region.It should be noted the risk of future strong earthquakes in these areas.In the adjacent interconnected tectonic areas,the blocks and faults are interrelated and interacted each other.When an earthquake occurs in a region,the rapid displacement and deformation of rock will inevitably lead to displacement and deformation of the associated blocks and faults; strain energy will transfer from one region to others.The numerical simulation results of deformation process in the Capital area from 1989 to 1998 clearly show that the high strain energy concentration region shifted from Datong area where 1989 earthquake(M_S 5.8)occurred to Zhangbei area where 1998 earthquake happened.It illustrates that the application of numerical simulation analysis method may help us predict the possible strain energy transfer process,thus,providing the reference target regions for earthquake monitoring.

The paper studies the coseismic changes of water level and water temperature caused by the M_S 8.0 Wenchuan earthquake.The differences of water level and water temperature variations caused by the M_S 8.5 Sumatra earthquake on Sep.12,2007 and the M_S 8.0 Wenchuan earthquake on May 12,2008 are analyzed.The result shows that the well water level change caused by Wenchuan earthquake is dominated by rising.Spatial distribution of wells with water level rising or descending exhibits regional difference.The proportion of wells is higher with water level and water temperature changes in the same directions than in the reverse direction.Water temperature mainly dropped when water level fluctuated.Compared to remote earthquake,near earthquake caused bigger changes in water level and water temperature in wells.Coseismic changes of all the well water level and most of water temperature kept the same direction regardless of distance,magnitude,focal mechanism of earthquakes or epicentral directions,though water temperature direction changes occurred only at some peculiar wells.The water temperature direction changes were caused by changes of artesian condition and water level response from fluctuations to steps.The direction of water level changes might be controlled mainly by both local geological structures and hydro-geological conditions of the well.However,the direction of water temperature relates with mixing of water in the well,the location of the water temperature probe and other factors.The mechanisms of water temperature coseismic change are more complicated.

This paper describes the structural profiles across such main boundaries between earth's crust and mantle as: granitic layer (G),inner granitic layer (G₁),Conrad boundary (C),M discontinuity (M),and M₁ and M₃ in upper mantle,for which a coverted wave has been used in the study area (E118°56′—119°40′,N31°10′—31°50′).The results obtained indicate that NE-trending structures are dominant beneath this area,and then NW-trending structures.The deep faults have been well developed and the two shocks have occurred at the granite layer.It has been concluded that the earthquakes tend to have occurred along the edge of the uprising zone or along the gradient zone where the depths to the boundaries vary,abruptly or at the intersections of the deep fault in different directions.