Based on the analysis of seismicity characteristics in northeast China, the following conclusions can be obtained: 1) We should make a concrete analysis from the time prosodic characteristics of the seismicity period in northeast China.The duration of the fifth active period, the number of earthquakes and other indicators,all show that the fifth period of seismic activity in northeast China has ended.
The magnitude 5.7 and 5.1 earthquakes in Jilin Songyuan in 2018 and 2019 may mark the beginning of the sixth active period in northeast China. 2)The main seismic areas in northeast China are located in Songliao basin and Greater Khingan range area from 2013 to 2019. The two regions have the activity characteristics of migration pair with the boundary line between Greater Khingan range and Songliao basin. By analyzing the migration trajectories of five groups, it is possible for future earthquakes to migrate to Greater Khingan range region. 3) The boundary between paired earthquakes and unpaired seismicity in northeast China is formed by the southern margin of Songliao basin.Since 1900, paired earthquakes in northeast China have occurred mainly in Songliao basin and Greater Khingan range region.The time interval between the paired earthquakes is 0.1 month to 37.0 months, the distance interval is as far as 309.0 km, and the magnitude difference is up to 0.7.A total of 27 earthquakes with a magnitude of 5.0 or above occurred in the Songliao basin and Greater Khingan range area, among which 24 earthquakes had paired activity and the incidence of paired earthquakes was about 89%.71% of the paired earthquakes occurred in the Songliao basin and 29% in Greater Khingan range region.The law of paired seismic activity is universal in Songliao basin and Greater Khingan range area and can be used as a prediction index. 4) Comparing the results of surface strain rate in northeast China from 2013 to 2015 and 2015 to 2018, the area of the most significant change is located in the middle of Songliao basin, which is also the area with the most significant change in northeast China. There is a risk of future earthquakes in the area. 5) Songliao basin will remain the main area of shallow seismic activity in northeast China.

In this study, the Shanxi area is divided into three areas of north, middle and south, using seismic event waveform data in and around 50 km in Shanxi province from 2009 to 2019, using linear fitting, reduced travel time, and Hyposat batch processing methods. The crustal velocity models of each subarea are determined, and three methods are used to verify the subarea model: batch positioning to compare residuals, PTD method to determine the source depth, and unnatural seismic events. The results show that the zoning model has better applicability to the Shanxi 2015 velocity model. The difference between the zoning model and the Shanxi 2015 velocity model is mainly reflected in the propagation velocity of the P-wave in the upper crust and Moho and the depth of the Moho. The zoning model shows that the propagation velocity of the crust gradually decreases from north to south, while the velocity of the Moho surface gradually increases, and the depth of the Moho shows a trend of thick north and thin south. The upper crust velocity value is higher due to the Datong volcano in the northern region, while the lower crust and Moho velocity are lower, and the crust thickness is thicker. The upper crustal velocity of southern region is lower, due to the existence of huge thick sediments.

In this paper, using double-difference tomography, we inverse the three-dimensional velocity structure of the Ruoergai region of Sichuan province. We obtain the fine 3D velocity structure and high precision source position parameters of the region. The inversion results show that the whole velocity structure of the study area is in a low-speed state, which reflects the partial melting material characteristics within the Qinghai-Tibet plateau. In the northeast margin of Qinghai-Tibet plateau, the strong structural deformation characteristics and the spreading direction of the low-speed region confirm the scientific speculation that the material overflows to the southeast. The stress accumulation results from the compression of the Qinghai-Tibet plateau plate and relatively hard Ruoergai block, so the Ruoergai series earthquakes occurred in the high and low-speed transition zone.

A spatiotemporal evolution characteristic image of the gravity field in the north Tianshan area is obtained using the multi-stage mobile gravity data from 2014 to 2019 combined with the classical adjustment calculation of absolute gravity points. The material migration pattern of main structural parts in north Tianshan area is obtained using the visualization method of gravity interval difference. Finally, the density of crust at different depths in the middle part of north Tianshan mountain is simulated by using compact gravity inversion method.The results shows that the best depth of crustal material density change is 30 to 40 km.The positive crustal density change area is basically located in the north slope of north Tianshan mountain and the southern edge of Junggar basin, which indicates that the material migration in this area is relatively concentrated, or that the crust presents the tendency of subsidence. However, near the mountain body, the change of material density presents a negative value; the crust is in the process of uplifting due to the tectonic stress of the mountain. 

We use the GRACE time-variable gravity field models released by the University of Texas Space Research Center (CSR) to determine the optimal Gaussian filter radius of the model based on the maximum SNR (signal-to-noise ratio) criterion. Therefore, we use the RL06 SH (spherical harmonics) model to study the TWSC (terrestrial water storage changes) of the Congo river basin from 2002-04 to 2020-05, analyze its spatio-temporal distribution characteristics, and explore the driving factors in combination with hydrological, precipitation and evapotranspiration data. Results show that the TWSC annual signals in the Congo river basin derived from the GRACE model are consistent with those from the land surface water estimated by the hydrological model, which indicates that the driving factor for the annual change of TWS in the Congo River Basin is surface water changes. Withrespect to inter-annual changes, the TWSC during 2002-04-2020-05 slightly increases, but decreases significantly from 2002-04 to 2006-12. The estimated results of RL06 SH models is -2.30±0.24 cm/a; there is an increasing trend from 2007-01 to 2010-12, which was 0.38±0.24 cm/a; The TWS has increased even more rapidly during the period of 2011-01-2020-05, with the trend of 0.92±0.12 cm/a.

We analyze the constant chemical composition and hydrogen, oxygen isotope and tritium activity data of observation well water, atmospheric precipitation, cold spring water, geothermal hot spring water and surface water samples in the Lushan area around Jiujiang. We show that the groundwater in the Lushan area is mainly divided into two hydrogeological units in the northwest and southeast.The hydration type represented by Jiujiangtai No.2 well water and Donglin Temple is HCO3-Ca type on the northwest side, while the hydration type represented by geothermal spring well water and Guanyinqiao spring is HCO3-Na type on the southeast side; the ion component mainly comes from weathering of crust rocks. Hydrogen and oxygen isotopes indicate that the groundwater in the Lushan area of Jiujiang belongs to the cause of precipitation, and some confined fractured well springs have deep circulation characteristics.Estimating the chloride ion indicates that the direct recharge rate of atmospheric precipitation is about 4.5%-33.27%. The formation of fissures and pressured artesian wells by infiltration recharge under atmospheric precipitation is the main cause of groundwater in Lushan area, a part of which is the formation of geothermal hot spring water through long-term and deep circulation of precipitation. The characteristics of Jiujiangtai No.2 well has both shallow surface water and circulation water, suggesting aquifers of two different recharge sources rise to the shallow bottom through different circulation paths, contributing to carrying part of the information of deep tectonic activity, is helpful to obtain seismic precursor anomaly information.

We obtain the high-spatial resolution crustal deformation velocity based on the interferometric synthetic aperture radar (InSAR). The interseismic creep velocity distribution and locking depth are inversed based on the InSAR deformation, using the deep and shallow seismic dislocation model. The results show that, firstly, Gyaring Co fault is a right-lateral strike-slip, with differential motion on both sides of the fault. From west to east, the differential motion on the fault gradually weakens. Secondly, InSAR deformation features are highly consistent with GPS observations, and the largest difference in far-field deformation is 4 mm/a(LOS). Thirdly, the analysis of the fault profile in the study area shows that the difference in crustal deformation on both sides of the Gyaring Co fault is the largest, which is the main fault that controls the long-wavelength signal in the area. Fourthly, the slip rate of the Gyaring Co fault is 2~6 mm/a, withthe locking area located at the range between Tangra Yum Co and Zigui Co.There is a risk of future earthquakes in this area.

We analyze the location andtectonic characteristics of the June 14, 2020 MW5.7 earthquake that occurred in Turkey, evaluating the seismic hazards. In this paper, we use D-InSAR technology to process the Sentinel-1A SAR data and GACOS is used for atmospheric correction to obtain line of sight coseismic deformation field. The LOS coseismic deformation field of descending track shows that the uplift on the north side and the subsidence on the south side of the fault. The maximum subsidence is about -7.75 cm and the maximum uplift value is about 8.87 cm. Constrained by LOS coseismic deformation, first we obtain the geometric parameters of the seismic fault are by Bayesian bootstrap optimization (BABO) method, and then the seismic rupture slip distribution is obtained by finite fault method.The inversion shows that the strike is about 257.48°±0.65°, the dip is about 79.69°±0.98°, the rake is about 154.2°±3.8°, the epicenter is (40.754°E,39.389°N). The length and width of the main rupture region are about 8 km×6 km, the shallowest buried depth is about 0.8 km, the deepest buried depth is about 8.9 km. The maximum slip on the fault is 0.57 m at the depth of 4.278 km. The seismic moment is about 4.54×1017 Nm (MW5.7), which agrees with the results published by the Turkey’s Disaster & Emergency Management Authority.The Turkey earthquake is controlled by a near EW blind fault and is mainly a dextral strike-slip with minor thrust. The earthquake caused the Coulomb failure stress to increase by more than 0.1 bar in some areas, and the future risk of these areas deserves more attention.

 Based on 44 COSMO-SkyMed satellite image data, the deformation information in the built-up
 area of Nanning from 2013 to 2016 is acquired by PS-InSAR technology. To verify the accuracy of PS-InSAR monitoring, we makes a field survey and detailed analysis of the deformation characteristics and reasons in view of the representative mutation areas. The results are as follows: The deformation rate in the study area is between -7－5 mm/a. The mutation points are mostly located in the area within the Nanning ring expressway, especially Qingxiu, Xixiangtang and Xingning districts. Among them, the land subsidence is obvious in the intersection area of Xinzhu road and Sixian road in Qingxiu district and the entrance and exit area of Minzu avenue, with a settlement rate of over -9 mm/a. Combining the engineering construction data and optical historical images, the results of the field investigation are in agreement with the problems reflected by the PS-InSAR monitoring data. The purpose of this paper is to provide new ideas for the government to forecast and prevent land subsidence disasters.

Using the removal-recovery method, the global atmospheric model and the pressure data of regional weather stations in the area around the Lanxin railway from 2012 to 2017, we calculate the influence of atmospheric load on the crustal deformation and gravity change in the 6 year period according to the atmospheric load theory. The results show that atmospheric load has an impact of about 1 cm on the vertical deformation of the Lanxin railway area, and less than 2 mm on the horizontal deformation. The impact on the vertical deviation is roughly 6 ms; on the ground gravity, the impact is roughly 6 μGal. The influence of atmospheric load on crustal deformation and ground gravity shows annual periodic and seasonal changes.

Based on the comprehensive calculation of CORS network baseline, we use the removal recovery and load deformation methods to monitor the influence of the terrestrial water loading on surface vertical deformation. Taking the Taizhou area as an example, the loading data of CORS network and related regional data from 2017 to 2019 are analyzed. The results show that the influence of terrestrial water loading on surface vertical deformation varies seasonally, and the groundwater loading influence is obvious, which can reach the centimeter level. The influence of terrestrial water loading on vertical deformation in Taizhou area is relatively stable on an interannual scale. The CORS network can monitor the surface vertical deformation caused by terrestrial water loading and can provide important reference for hydrodynamic environmental monitoring and geological disaster monitoring.

The co-seismic deformation field of the MW7.1 and MW6.4 earthquakes in California is extracted using the frequency domain cross-correlation algorithm based on the Landsat-8 and Sentinel-2 optical images.At the same time, we use some error processing algorithms, such as the least square polynomial fit, the method of improved mean subtraction, and so on, to reduce the system errors often caused by orbit error, banding error and temporal decorrelation. The results show that the maximum slippage of the fault trajectory caused by the MW6.4 foreshock is 1.05 m and the surface rupture trajectory is 15 km while the maximum surface slippage of MW7.1 main shocks reaches 2.82 m and the surface fault trajectory is 55 km. We speculate that the two earthquakes formed a typical conjugate characteristic, which is controlled by NNW and NE strike-slip faults.

In order to improve the efficiency of GNSS high-dimensional ambiguity resolution, this paper proposes an improved GNSS ambiguity fast decorrelation algorithm. The algorithm adopts a symmetric rotation sorting strategy and a delayed decorrelation strategy to improve the integer Gaussian transform algorithm of the lower triangular Cholesky decomposition. Verification through simulations and measured data experiments shows that the improved algorithm reduces the number of conditional variance exchanges and integer Gaussian transformations in the decorrelation process to a certain extent, thereby effectively improving the efficiency of the original algorithm and enhancing the stability of the calculation time.

In this paper, the data of five individual IGMAS stations in China from doy 112 to 116 in 2020 are selected to analyze and compare the positioning accuracy of static and kinematic PPP.The results show that accuracy of R,A,S directions of the B2b orbit product is better than 0.07 m,0.33 m,0.24 m,the clock difference STD is better than 0,08 ns, the RMS of static PPP can reach 0.8 cm, 1.5 cm, 1.6 cm in N, E and U components, while 3.6 cm,6.0 cm, 12.2 cm for kinematic PPP, which satisfies the LBS and geodetic survey applications.

We compare the characteristics of PPPH, MG-APP and GAMP software, select the observation data of six MGEX stations, use the three PPP software to solve the GPS single system and GRCE multi-system precise point positioning, and compare the positioning accuracy, convergence time and tropospheric delay of the three software solutions. The results show that the positioning accuracy and convergence time of GRCE multi-system solved by three software are improved as compared with GPS single system, the positioning accuracy of MG-APP and GAMP is almost the same, while PPPH is slightly worse, and the convergence time of MG-APP is shorter than that of PPPH and GAMP. The GPS and GRCE static precise point positioning calculated by the three software is better than 1 cm horizontally and better than 2 cm vertically. The GPS dynamic precise point positioning calculated by the three software is better than 2 cm horizontally and better than 5 cm vertically. The GRCE dynamic precise point positioning calculated by the three software is better than 2 cm horizontally and is better than 3 cm vertically. The ZTD calculated by the three software are consistent with the ZTD released by IGS, which can meet the accuracy requirements of the ZTD. The stability of ZTD calculated by GAMP is slightly higher than that of PPPH and MG-APP.

The problem of long convergence time restricts the development of precise point positioning (PPP)technology in the application field. In order to improve the positioning accuracy and convergence speed of PPP, we propose an ionosphere-constraint model based on uncombined and unconstrained model, and the high-precision regional ionospheric a priori information constraint method. We use the observation data of 183 reference stations in the west coast CORS network of the United States to model the regional ionosphere, obtain high-precision ionospheric delay information, and compare and analyze through experiments, the PPP positioning performance of the three algorithms: ionosphere-free, uncombined and unconstrained and ionosphere-constraint model. The experimental results show that the additional ionospheric constraint algorithm has better model geometric strength. Compared with the first two models, the PPP 10 minutes before the positioning process, this algorithm can significantly improve the convergence speed and positioning accuracy of PPP positioning.

We analyze the influence of errors such as pole shift, tidal nutation, and constant deviation matrix in the process of ITRS to J2000, and analyze the impact of seasonal changes, solar activities, geomagnetic activities, etc. on the accuracy loss of coordinate conversion. The coordinate analysis of the IGS precision ephemeris data of 2019 shows that the coordinate conversion error caused by the tide and nutation is 0.44 m, the spring coordinate conversion error is 0.23 mm, and the spring coordinate conversion error is about 3 times that of summer, autumn and winter. The constant deviation matrix can affect the coordinate conversion error by 1.7 m. The error correction term is added to the orbit conversion of the neutral atmosphere occultation inversion. The tidal nutation and the constant deviation matrix cause the error effects of 0.09 K and 0.19 K respectively on the inverted temperature products. It is recommended to use the high frequency correction of tidal nutation in the inversion of GNSS radio occultation, and it is recommended to perform a constant deviation matrix for rotation processing during the conversion of ITRS to J2000.

The Kuwait 3D project is a high count channels (over 200 000 channels in a live super-patch) project which firstly applies INOVA’s G3iHD acquisition system and the SL11 digital sensor. The project uses a single-point receiving, sub-line combined geometry, and the data is a digital group forming indoors to improve the signal-to-noise ratio and resolution. However, after technical staff processed the data, we find that the high-frequency components of the data are seriously attenuated. This paper investigates the reasons for the attenuation of high-frequency signals in Kuwait through experimental analysis and geological research. Geological structure is the main reason for the high-frequency attenuation.

Based on the seismic records of Jiangsu strong motion network and Jiangsu seismic network, using the method of real-time simulation of WA records in time domain we carry out ML determination of earthquakes with M≥2.3 recorded from 2007 to 2018.In order to quantitatively analyze the reliability of local magnitude measurement based on acceleration, this paper first uses the determination method and gauge function specified in the new national standard of magnitude to determine the magnitude based on acceleration record, and compares the measured result with that measured by Jiangsu seismic network based on velocity record, and obtains the linear fitting relationship：ML(ACC)=0.987ML+1.371. We also calculate the absolute deviation between 15 324 groups of magnitude based on acceleration measurement and manual cataloging magnitude. The results show that 87% of the results with the deviation are within ±0.5 level.After 4-order polynomial fitting, we find that the magnitude measured in the range of less than 200 km is slightly lower than that of manual cataloging, and there is no systematic deviation after the epicenter distance is 200 km. Generally speaking, the results of the two methods are in good agreement. The results show that it is feasible and reliable to use acceleration records to simulate WA displacement records to calculate ML magnitude.

We use the frequency spectrum method to process the observation data of multiple seismographs in Sichuan and analyze the spectrum characteristics of the data before the 2008 Wenchuan earthquake. The results show that obvious abnormal disturbances occurred 3 to 4 days before the earthquake. The dominant frequency ranges of abnormal signals are 0.18 to 0.25 Hz and 0.1 to 0.18 Hz. The signals in the frequency band of 0.18 to 0.25 Hz are mainly affected by the western Pacific typhoon. The signal anomaly started on May 9th, reached its maximum intensity on the 11th, and then began to attenuate; while the signal in the 0.10-0.18 Hz frequency band gradually increased from May 9th, increased sharply 10 hours before the earthquake, and reached the strongest before the earthquake. Signals in the frequency range of 0.10 to 0.18 Hz change sharply before the earthquake. The analysis results of all stations are similar, which may be related to the incubation of the earthquake.