As one of the most serious geological disasters, earthquake is of sudden and destructive characteristic. Therefore, it is of great significance to earthquake monitoring and early warning. The phenomenon of surface thermal infrared radiation enhancement is a common precursor of moderate and strong earthquakes and has been used as an important reference information for early warning and short term prediction. A variety of explanations have been given to understand internal mechanism of the above phenomenon, in which the stress-induced heating hypothesis is widely accepted and has been confirmed in the laboratory rock mechanical loading experiments, that is, under ideal conditions in the laboratory, the rock heats up when it is pressed and cools down when it is stretched. Under field conditions in practice, however, weak seismic precursors of thermal anomalies are often interfered by various environmental factors(solar radiation, atmospheric movement and human activities, etc.), and it has not been investigated whether the corresponding relationship between the above crustal compression-extension motions and thermal radiation anomalies can be observed under field conditions. The earth's gravity field, as one of the basic physical fields of the earth, contains the density distribution of crustal structure, which can be served to study the migration of the earth's material, the deformation of the crust and the change of the stress field. In this paper, we use GRACE gravity and MODIS thermal infrared remote sensing data to verify the stress-induced heat hypothesis in the field with Wenchuan earthquake as the time node. Firstly, the crustal mass density obtained by GRACE satellite was compared with thermal infrared radiation. Then, the gravity anomalies extraction method based on maximum shear strain and in-situ temperature method were used to obtain the gravity anomalies and thermal anomalies respectively. Furthermore, the correlation between the two anomalies before the earthquake was detected from the time scale and space scale respectively, and the consistency analysis between the above anomalies and the spatial distribution of the tectonic fault zone was carried out. For this purpose, two important indicators i.e., anomaly intensity and anomaly distribution, were established in time domain and space domain, respectively. The following conclusions could be drawn: 1)The stress-induced heating hypothesis can be verified by remote sensing in field conditions. The warming zone of the crust(positive thermal offset index)corresponds to the compression zone, and the cooling zone(negative thermal offset index)corresponds to the stretching zone. The consistency of positive and negative variation between the crustal mass density and thermal offset index is 88.9%, which provides field observation evidence for the stress-induced heating hypothesis. 2)The spatio-temporal variation of gravity anomalies and thermal anomalies before earthquake has strong correlation. In the time domain, there is a strong correlation between the gravity anomalies and the thermal anomalies, which shows that the intensity of the two anomalies suddenly increases synchronously and reaches the maximum simultaneously three months before the earthquake. In the spatial domain, gravity anomalies mostly occur at the junction of positive and negative values of thermal offset index, which indicates that the spatial distribution of gravity anomalies and thermal anomalies also has a certain correlation. In addition, the two anomalies appear to be distributed along the fault zone for many times, which shows that they are closely related to tectonic activities.

The terrain in southeastern Tibet is steep and the valleys are crisscrossed. Since the Quaternary, glacial ice and debris have blocked the course of the Yarlung Tsangpo River and its tributary river valleys to form giant dammed lakes, and the huge flood deposits formed by the dammed lake outburst floods are often associated with moraines, ice water deposits, lacustrine deposits, aeolian sand or other running water sediments to form complex river valley accumulation landforms. Different types of sediments in alpine and canyon areas are similar in morphology, structure and fabric, and are difficult to distinguish. Grain size and morphological characteristics are the most important structural characteristics of sediment, and the distribution rules are controlled by many factors such as sedimentary environment, physical properties of detrital material, transporting medium and transporting mode, etc., which is an important proxy index for restoring paleoclimate and inverting paleoenvironment. However, the relevant research on identifying sediment types in alpine valley area of southeast Tibet by grain size and morphology index is still in the exploratory stage. In order to understand the particle size characteristics and spatial differentiation laws of outburst flood sediments and the micromorphological characteristics of particle surfaces, we collected 33 samples of Holocene flood retention sediments preserved along the river within about 350km from the outlet of the Jiacha Gorge in the middle reaches of the Yarlung Tsangpo River to Pai Town, and measured them with Malvern 3000 laser diffraction particle size meter and Zeiss Signma scanning electron microscope, combined with digital geomorphology(DEM)data extracted river channel width and steepness coefficient. The features of spatial distribution law of particle size are analyzed, and the following understanding is obtained. The particle size of outburst flood retention deposits is characterized on the whole by fine-silty sand(2.57~5.18Φ)with poor sorting, positive skew and narrow peak state. Two end element models are obtained: The main peak of EM1 terminal element is 3.16Φ, with an average percentage content of 42.7%, which may represent the alluvial characteristics of higher energy of outburst floods in alpine valley areas, and the main peak of EM2 terminal elements is 2.06Φ with an average percentage content of 55.6%, which can be used to indicate the accumulation process of the outburst flood lag deposits. Affected by the width of the river, the EM1 content has a tendency to increase downstream, while EM2 has the opposite trend. The surface microstructure of quartz particles in the outburst flood lag deposits is mainly characterized by mechanical scratches, shell-like fractures, upturn cleavage and cleavage steps, with low structural maturity, mostly angular shape, and rare denudation pores of chemical origin. As a typical representative of climbing sand dunes in the valley area of the semi-humid monsoon area, the genesis of the dunes is of great guiding significance for revealing the source of sand dunes in the valley area of the alpine valley area, identifying paleoflood deposit and aeolian deposit, distinguishing aeolian deposit and paleoflood slackwater deposits on both sides of the riverbank, and windbreak and sand fixation engineering in the Yarlung Tsangpo River. By comparing the particle size and surface micromorphology characteristics of the known outburst flood deposits of the Yarlung Tsangpo River, we believe that the sand source of the Fozhang dunes is mainly from the outburst flood deposits and was transformed later by wind forces.

The occurrence of earthquakes is closely related to the crustal tectonic movement and the migration of earth mass, which consequently cause the changes of the earth‘s gravitational field. Global time-varying gravity field data obtained by GRACE gravity satellite can be used to detect pre-seismic gravity anomalies. For example, gravity signals caused by several large earthquakes, such as the 2005 M_W8.6 Indonesia earthquake, the 2010 M_W8.8 Chile earthquake and the 2011 M_W9.0 Japan earthquake, have been successfully extracted using GRACE data. However, previous studies on GRACE satellite-based seismic gravity changes focused more on the dynamics of the co-seismic gravity field than on the pre-seismic gravity anomalies which are of great significance for the early warning of earthquakes. Moreover, the commonly adopted difference disposal of the gravity field with the gravity field of adjacent months or the average gravity field of many years when obtaining gravity anomalies cannot effectively remove the inherent north-south stripe noise in GRACE data. On the contrary, it is more likely to cause the annihilation of the medium-high order information in GRACE gravity field model, which results in the loss of some gravity information related to tectonic activities. To explore the pre-seismic gravity anomalies in a more refined way, this study proposes a method of characterizing gravity variation based on the maximum shear strain of gravity, inspired by the concept of crustal strain. In other words, the gravity strain tensor is obtained by further calculating the second-order gradient of the increment of disturbance potential after the removal of hydrological disturbance, and then the maximum shear strain of gravity is ultimately generated to characterize the pre-earthquake tectonic activities. Then, to better understand the seismogenic process of the fault zone by further extracting the pre-earthquake anomalous changes, the data of the maximum shear strain time series are analyzed in this study by means of the offset index K to describe the gravity anomaly. Because the maximum shear strain is calculated by the second-order gradient of GRACE gravity field, this method can suppress the stripe noise better than the difference disposal, thus effectively improving the sensitivity of gravity anomaly detection. The exploratory experiments are carried out in the Tibetan plateau and its surrounding area, which locates among the Pacific Ocean, the Indian Ocean and Eurasia, with the highest altitude, most complex topography and frequent strong earthquakes. Ultimately, the Wenchuan earthquake and Nepal earthquake were used as an example to complete the extraction of pre-earthquake gravity anomaly information by the above method, and the pre-earthquake tectonic activity of the fault zones was analyzed. The results show that a large area of gravity anomalies consistent with the spatial distribution of the fault zone appeared on the Longmenshan fault zone during the half a year before the earthquake, and the maximum anomalous value appeared within 50km from the epicenter, while no anomalies appeared during the non-earthquake period. In addition, compared with the traditional methods, the proposed method has a better ability to extract anomaly information of gravity field, which provides a new idea for understanding the dynamic mechanism of large earthquakes using GRACE data.

The Xijiang Fault is an important NW-trending fault with a length of~200km, located in the western part of the Pearl River Delta. A M4 3/4 earthquake occurred at the northern end of the fault(Sihui)in 1445 and a magnitude 5 earthquake occurred at the southern end of the fault(Modaomen Waters)in 1905. Heshan is the boundary between the southern and the northern segments of this fault. The southern segment which is called Heshan-Modaomen segment is mainly hidden faults. The activity of Heshan-Modaomen segment remains controversial due to the lack of systematic studies for the deep and shallow exploration, which affects the assessment and prevention of earthquake disaster risk. In this paper, we concentrate particularly on the distribution and activity of Heshan-Modaomen segment using seismic geological surveys, shallow seismic exploration, joint borehole profile detection, and Quaternary geochronology.
Field geological surveys show that the fault zone is prominently normal sinistral strike-slip faults, striking about N310°~330°W, with a width of 10~20m. Most of them dip northeast at angles of 60°~80°. Observations on typical outcrop show that cataclasite, breccias and siliceous rocks are developed on the faults. Fault planes often have smooth and polished surfaces and no fault geomorphology has been developed along the fault zone. The overlying eluvial weathered soil materials have not been disturbed or cut. We carried out shallow cross-fault sounding of 7 profiles in the hidden section of the fault zone using longitudinal wave reflection method of multifold coverage observation system. As a result, we obtained the reflection time sections of the target stratum and the main structure. A total of 13 breaking points to be investigated were explained. We also performed cross-fault drilling at the location of the seismic data interpretation profile and catalogued drilling cores. ¹⁴C and OSL samples were collected systematically. The ¹⁴C dating was performed by the BETA Laboratory in the United States and 16 valid age data were obtained. OSL dating was performed by the OSL Laboratory of China University of Geosciences(Wuhan)and 6 age data were obtained.
This paper presents the study results of two representative cross-fault profiles. The shallow exploration survey line XJ1 and the row drill profile P1 are located in the southern section of the fault where six boreholes are arranged. We find the existence of bedrock faults on the joint borehole profile. The grooves developed thereupon are filled with the late Pleistocene paleochannel deposits with no obvious faults observed. The overlying Holocene strata are horizontal and continuous, without cutting and disturbance. Combined with the stratigraphic age, we infer that the fault has been inactive for at least about 11 000 years. The shallow exploration survey line XJ2 and row drill profile P3 are located in the northern section of the fault, where a total of seven boreholes are arranged. The borehole sections reveal the existence of fault crushed zone in the underlying bedrock(Cambrian hornstone). The tectonites are mainly fault breccias and cataclastic rocks with chlorite alteration. Groove landforms are formed along the fault zone with strong erosion at the later stage, and filling and accumulation occurred since the Holocene transgression with no fracture cutting or stratum disturbance. According to the landform, the occurrence of faults and the development of transverse active faults, the Heshan-Modaomen segment of Xijiang Fault can be further divided into two segments with the boundary of Zhupai Island. Both of them have been inactive since the Holocene.

Small earthquakes have been recorded in Yibin area, Sichuan Province since 1970, the frequency and intensity of seismicity have shown an increasing trend in recent ten years, and the earthquakes are distributed mainly in Changning, Gongxian and Junlian areas. Based on the seismic data from January 2008 to May 2015 recorded by Sichuan and Yunnan regional networks and Yibin local network, seismicity analysis, precise location and velocity structure inversion for earthquakes in Yibin area are carried out, the three-dimensional spatial distribution of seismic activity and the velocity structure at different depths in this region are investigated, trying to analyze the seismic activity law and seismogenic mechanism in Yibin area.
The earthquake relocation result shows that the spatial cluster distribution of earthquakes is more obvious in Yinbin area, the earthquakes are concentrated in Changning-Gongxian and Gongxian-Junlian regions. The seismic activity presents two dominant directions of NW and NE in Changning-Gongxian region, and shows asymmetric conjugate distribution, the long axes of NW-trending and NE-trending seismic concentration area are about 30km and 12km respectively, and the short axes are about 5km. There is a seismic sparse segment near Gongxian, the frequency and intensity of seismicity in the southeast side are obviously higher than that in the northwest side, and the earthquakes with larger magnitude are relatively deep, the focal depth is gradually shallower with the distance away from Gongxian. Seismic activity is sparse in the west and dense in the east in Gongxian-Junlian region, the predominant direction of earthquakes in the seismic dense area of the eastern segment is NE. Seismic activity extends in opposite direction in the easternmost part of the two earthquake concentrated area.
The P-wave velocity structure at different depths in the study area is obtained using joint inversion method of source and velocity structure. In view of the predominant focal depth in this region, this paper mainly analyzes the velocity structure of the upper crust within 10km. Within this study area, the P-wave velocity of earthquake concentration areas is relatively high within 10km of the predominant focal depth, especially in the northwest of Gongxian and eastern Junlian area, the P-wave velocity on the southeast of Gongxian increases gradually with depth, especially at 6km depth. These high-velocity zones are generally related to brittle and hard rocks, where the stress is often concentrated.
Comparing earthquake distribution and velocity structure, seismic activity in this area mainly occurs in high-low velocity transition areas, the inhomogeneity of velocity structure may be one of the factors controlling earthquake distribution. The transition zone of high and low velocity anomalies is not only the place where stress concentrates, but also the place where the medium is relatively fragile, such environment has the medium condition of accumulating a large amount of strain energy and is prone to fracture and release stress.

Analysis of stress state of faults is helpful to understand crustal mechanical properties and seismicity. In the paper, we invert the horizontal crustal stress field in the southeastern Tibetan plateau using focal mechanism solutions of small and medium-size earthquakes, and apply them to estimate the stability of regional major faults.
Firstly, we collect focal mechanism solutions of small and medium-sized earthquakes in the southeastern Tibetan plateau. The dataset includes more than 1 000 focal mechanism solutions in the past twenty years. Magnitudes of these earthquakes vary from M3.0 to M6.0. Most of the focal mechanism solutions were determined using waveform inversion technique. Although most of focal mechanism solutions in the southeastern Tibetan plateau are strike-slip faulting, their spatial pattern is different in sub-regions. Normal faulting earthquakes mainly occurred in the western Sichuan region, reverse faulting earthquakes mainly occurred in the boundary zone between the Tibetan plateau and the South China craton, and strike-slip faulting earthquakes mainly occurred in the central and southern Yunnan region.
Next, we settle on a mesh with grid spacing of 0.5° in longitude and latitude in the region and invert the horizontal crustal stress field at each grid point. Spatial variation of the maximum principal stress axis in the southeastern Tibetan plateau shows a clockwise rotation around the eastern Himalaya syntax. The azimuth of maximum compressional stress axis is about 88.1° in the western Sichuan region, about 124.6° in the South China craton, and about 21.6° in the western and southern Yunnan region. The azimuth of regional maximum compressional stress is nearly parallel to the direction of terrain elevation gradient, and that of the minimum compressional stress is nearly parallel to the tangential direction of the topographic elevation contours. The spatial pattern reflects the control role of gravity spreading of the Tibetan plateau on the regional horizontal stress field.
Finally, we analyzed regional fault stability based on these collected focal mechanism solutions. The fault instability parameter (I) is defined based on the Mohr-Coulomb criterion and indicates the degree of fault approximating to rupture. The instability parameters on fourteen major faults in the southeastern Tibetan plateau were calculated. Our results show that the stability of the Lianfeng-Zhaotong Fault is the lowest before 2014 in the region, which indicates the fault zone is close to rupture at that time. Our results provide a new useful tool to assess regional seismic potential using dense focal mechanism solutions.

Two earthquakes with magnitude larger than 7.0 occurred in 2008 and 2014 on the southwestern end of the Altyn Tagh Fault, which is located in the northwestern borderland of Tibetan plateau. Occurrences of these two earthquakes provide important insights into regional geodynamics and potential seismic risk. Layered viscoelastic model is employed in the paper to study the interaction between these two events. We find that most of aftershocks were triggered by coseismic stress produced by the 2008 Yutian earthquake, and the effect of this earthquake is insignificant on the occurrence of the 2014 Yutian earthquake. However, stress transfer by viscoelastic relaxation of postseismic deformation is in favor of occurrence of the 2014 Yutian earthquake. The coseismic and postseismic stress transfer produced by the 2014 Yutian earthquake leads to stress increasing on the western segment of the Altyn Tagh Fault. Since the occurrence time of the last major earthquake on the western segment of the Altyn Tagh Fault is tens of years ago, it should have accumulated large moment deficit on the fault segment. The Altyn Tagh Fault should be considered as a fault with high potential seismic risk.

Using double-difference precise location results of seismic S wave data from 2000 to 2012, distribution and variation of dynamic moving average Q_s value are imaged in Hainan Island and adjacent regions through seismic attenuation tomography. We explore regional crustal S-wave attenuation characteristics of temporal and spatial variation combined with seismic activity, volcanoes and heat distribution, and GPS baseline changes. The results show that:(1)Attenuation imaging shows that there is a significant lateral heterogeneity in Q_s distribution in the study area and the Q_s values are high in the central region and low in the north and south regions of Hainan Island. Low-Q_s areas are baseically converged to the north of Wangwu-Wenjiao Fault, to the south of Jianfeng-Diaoluo Fault, and to the east of Puqian-Qinglan Fault. Earthquakes are basically converged to the edge of the transitional regions of high and low Q_s values. Heat flow sites and volcanoes zones are located in low-Q_s area in the region. (2)There is a strong correlation between dynamic moving average Q_s value, seismic activity and Luzhou-Qiongzhong GPS baseline. From 2000 to 2008, the average Q_s value of the study area is relatively high, the seismic activity is strong, and Luzhou-Qiongzhong GPS baseline is decreasing. From 2008 to 2012, the average Q_s value of the study area shows a downward trend, the seismic activity is weak, and the Luzhou-Qiongzhong GPS baseline displays an elongation trend.

In the paper,we use 296334 P_n rays from 27777 earthquakes recorded by 1354 seismic stations in the eastern Asia region,an area spanning from 15癗-60癗 and 60癊-145癊,to invert the P_n velocity structure of uppermost mantle and its lateral variations. We also discuss the tectonic implication of the lateral variation based on the P_n velocity structure. Inversion results show that the mean velocity of P_n is 8.03km/s in the eastern Asia region. The lateral variation spans from -0.42km/s to 0.41km/s. Two different tectonic regions can be identified according to distributions of P_n velocity and its lateral variation. In the region from the boundary of the Pacific plate to the east of 108癊,i.e.the eastern China,P_n velocity is relatively low. In the region located at west of 108癊,P_n velocity is high. The different distribution of P_n velocity is consistent to the regional geodynamic background. The dominant geodynamic effect is subduction of the Pacific plate in the eastern China and collision of the Indian Ocean plate in the western China. At the same time,P_n velocity is relatively low in active tectonic regions and high in the stable tectonic regions. The P_n velocity also shows negative correlation to the regional seismicity. The higher of the seismicity,the lower of the P_n velocity,and vice versa. The negative correlation indicates the relationship of lateral variation of P_n velocity and tectonic deformation with seismicity level. The region with low P_n velocity usually is a region with high tectonic deformation and intensive seismicity.

Because b-value can be used as an indicator to measure the level of crustal stress,the seismicity pattern recognition based on b-value is considered as one of the most intuitive methods for earthquake forecast research and experiments. The intense seismicity in the Sichuan-Yunnan region makes the area to be an ideal field for earthquake forecast experiment. We investigated the spatial and temporal variations of b-values before nineteen earthquakes with M≥6.5 in the Sichuan-Yunnan region from 1981 to 2008 using regional small earthquake data. The results show that spatial b-value variations portending M≥6.5 earthquakes in the Sichuan-Yunnan region are insignificant. Less than 50%of the major earthquakes occurred in the regions with low b-values relative to the entire study area. In terms of temporal evolutions,the b-values in seismic source regions showed a systematic drop before the occurrence of earthquake. They showed an obvious decreasing trend during the period one year prior to strong earthquakes in 58%of the seismic source regions. Combined with other geological and seismological data,the short-term seismicity data can provide certain enlightenment for the estimation of potential seismic hazard in specific regions.

The 14 November 2001 M_S 8.1 Kunlun earthquake at northern Tibet is the largest earthquake that occurred in the Chinese continent since 1950.We apply a three-dimensional(3-D)finite element numerical procedure to model the coseismic displacement and stress fields caused by the earthquake dislocations,which are constrained by field investigations.We then further investigate the stress interaction between the M_S 8.1 earthquake and the intensive aftershocks.Our primary calculation shows that the coseismic displacement field is centralized around the east Kunlun Fault zone.And the attenuation of coseismic displacements on the south side of Kunlun Fault zone is larger than that on the north side.The calculated coseismic stress field also indicates that the calculated maximal shear stress field is centralized around the east Kunlun Fault zone,and the directions of the coseismic maximal principal stress are contrary to that of the background crustal stress filed of Tibet Plateau.It indicates that the earthquake relaxes the crustal stress state in Tibet Plateau.Finally,we study the stress interaction between the M_S 8.1 earthquake and its intensive aftershocks.The calculated Coulomb stress changes of the M_S8.1 great earthquake are in favor of triggering 3 aftershocks.

The depth of Quaternary in China coastal zone varies greatly.In most areas,silt,clay and sand are always multiply interbedded.This kind of formation can attenuate greatly the high frequency signal,and is unfavorable to propagation of seismic wave.At the same time,the density of population in the area is much higher and the industrial noise is strong,so the trigger and receiver conditions are not ideal.The paper presents some application examples of detecting buried faults with near-surface seismic methods in east Guangdong,Tianjin and Tangshan where the thickness of overburden varies greatly,and systemically introduces the methods of fieldworks,data processing and explanation approaches.It also illustrates the effective methods of how to improve SNR and resolution in environment with strong noise.In the application,the signal of refection is strong and the buried faults can be reflected evidently.Proofs of drilling at both sides of the faults approve that the depth of interface,location of fault point and throw of basement determined by seismic exploration are all reliable.The techniques and methods mentioned in this paper are of important reference value in urban active fault detection and engineering geophysical prospecting in similar areas.

Shallow seismic exploration is the main technique in present urban active faults detecting.The detection precision is not only affected by the factors of sources and receivers,but also closely related to the precision of seismic data processing.Velocity analysis is an important step in seismic data processing,which determines the precision of NMO,CDP stack,post-stack migration and time-depth conversion.Considering the properties of low stack folds,shallow objected layers and big background noise of shallow seismic data,the parameters selection for velocity analysis is studied in the paper.Firstly,by analyzing the offsets of different traces in adjacent CDP gathers,and comparing between single and multiple CDP gathers,the principle of how to extract large CDP gathers is proposed.And then,through comparing the velocity spectra derived from different large CDP gathers,velocity scanning interval,time window length,cutting ratio of NMO,etc.,some effective advices on parameters selection for velocity analysis are given,and meanwhile,several noticeable problems in velocity analysis and time-depth conversion are discussed.

Based on the research and the division of the active tectonic blocks and their boundaries in Chinese mainland, the feature of the large earthquake activities in the 24 boundaries between the 6 grade Ⅰactive tectonic block regions and the 22 grade Ⅱ active tectonic blocks are studied. The seismicity levels on the active tectonic block boundaries are discussed considering the large earthquake frequency and the released strain energy in unit distance and time. And then, the theoretic maximal magnitude and the recurrence period of each boundary are calculated from the G-R relation. By comparing with the actual earthquake records, it is found that the intensities of the earthquake deduced from the seismic activity parameter (a/b) in the main active boundaries in Chinese mainland are consistent with that of the nature earthquakes. Meanwhile, an inverse relation is found between the recurrence period of large earthquake and the tectonic motion rate on the boundaries. These results show that the a, b value of each boundary obtained in this paper is valuable. In addition, the present seismic activities and hazards of these boundaries are also probed into with the historical data and their elapsed time on each boundary based on the hypothesis that the large earthquakes satisfy Poisson distribution.

Earthquake is the best information source for describing the present-day crustal tectonic zones and crustal stress field,containing comprehensive and abundant geodynamic connotations. Based on the distribution of global earthquakes and their kinematic and dynamic characteristics,the most active global-scale tectonics can be divided into three first-order tectonic systems:the circum-Pacific deep subduction tectonic system,the mid-oceanic ridge tectonic system,and the continent-continent shallow underthrusting tectonic system. This paper describes in detail the types of faulting of seismic source,the characteristics of seismicities and focal depth distribution in global scale and in the afore-mentioned three tectonic systems,by using the Harvard CMT catalogue,which provides various parameters of hypocenter. Furthermore,the differences of faulting types,seismicities,and distributions of focal depths in different tectonic systems are discussed as well. The results show that different tectonic systems posses different environment and geodynamical force.

The three-dimensional structure of the ground fissure zone in the area of Datong Railway Bureau is studied in detail form the data of field investigation, geological trenching and shallow seismic prospecting, as well as analyis of its neotectonic background and underground water overextraction. The developing ground fissure zone has been propagating westwards at a rate of 260 ～ 520 m/a since 1983; Its differential movement rate across the zone reaches 22.1～24.4mm/a. The extensional rate of the main fissure is 1.11～11.6mm/a, vertical slip rate about 0.2～8.57mm/a, and left-lateral slip rate about 1.87～3.57mm/a. Its active behavior belongs to a brittle-plastic model. This ground fissure zone has been caused by the recent creep along the Baimacheng fault-aburied active fault. The local overextraction of the underground water has accelerated the development of the ground fissure zone. The formation of the ground fissures is an aseismic geologic hazard.

Fuzhou basin is one of the typical basins on southeastern margin of China continent In the basin two groups of faults have been found. There are NNW-NW-and NNE-NE-trending faults. The NNW-trending Ba'yi reservoir-Wangjuan fault is active and also is a well-known heat-flow anomaly zone.The calculation of striats along the faults on the bedrock outcrops within the basin and its boundaries by using Etchecopar's computerized method shows that there were four important stress fields since Yanshanian phase. The first stress field was compressive in NW-SE orientation, which caused reverse fault, schistosity and mylonite zone to be formed. The second was compressive in SN or NNE orientation, but in the state of compression which produced Paleogene diabase dykes along NNE-trending faults. The third was compressive in nearly EW or WNW orientation, R = 1, σ₂=σ₃, but in a extension state. The evidence for the third stress field is tension-shear horizontal striation on the walls of the basic dyke formed from Neogene to Quarternary. For the fourth stress field maximum principal compressive stress was vertical, indicating that the basin is in an exten-sional tectonic environment.

From new data of tectonic evolution,fault activity,neotectonic movement,recent tectonic activity and seismicity in Beijing area,the authors suggest that the characteristics of neotectonic movement in the northern and southern parts of this area are different. Neotectonic activity in the southern part is weaker than that in the northern part. Seismic risk in the future has also the same tendency.