We use the template matching method of waveform cross-correlation to pick up the missing earthquakes of the Changqing 4.1 earthquake sequence on February 18, 2020, and construct a high-resolution sequence catalog. Then, we use the spatial distribution of the sequence to quantitatively fit the geometric shape of the seismogenic fault plane, and combine with the focal mechanism solution of the 4.1 earthquake to comprehensively determine the seismogenic structure and possible causes of the Changqing earthquake sequence. The results show that 79 seismic events are identified and located by waveform cross-correlation scanning, which is 1.7 times the original seismic catalog. The dominant strike of the sequence and the focal mechanism solution of the largest earthquake indicate that the seismogenic structure of the sequence is a sinistral strike-slip buried normal fault with a strike of 302° and a dip of 88°. Based on the characteristics of structures and faults near the sequence, it is considered that the occurrence of Changqing 4.1 earthquake sequence may be caused by the heterogeneity of stress field in the tectonic composite position.

We present an overview of previous deep seismic sounding(DSS) results in Henan region along with a review of crustal structure features. The results show that: 1) The north China plate in north-central Henan province is characterized by a simple upper-middle-lower stratification, mirror-symmetrical deep and shallow tectonics and widely developed low-velocity bodies in the crust, while the crust of the Qinling-Dabie fold belt in the south is characterized by a highly laterally variable velocity structure, high velocity domes, large dip intracrustal reflective interfaces and Moho interfaces in the form of septal folds. 2) Changes in crustal thickness in the north China basin occur mainly in the middle and lower crust, while the upper crust is more uniform in thickness. The absence of mountain roots in the deep crust of the Qinling-Dabie fold belt reflects the strong slip action of the lower crust along the Moho surface. 3) The characteristics of earthquake distribution in different regions of Henan province are closely related to the velocity structure of the crust. The distribution of earthquakes in Puyang is controlled by high-speed anomalies, in Xuchang it is controlled by a combination of crustal media and regional fractures, while in Nanyang it is mainly controlled by the stratified structure of the crust.

We use the observation data of GPS reference stations, GPS observation profiles of cross-fault flow and cross-fault leveling sites in Fujian province from 2009 to 2020 for fusion processing. We use negative dislocation model of Defnode to invert slip rate, fault locking and fault slip deficit rate of major tectonic faults in Fujian. Combined with the results of surface horizontal strain rate near the main tectonic fault zones in Fujian using the least square configuration method, we evaluate the seismogenic risk of major structural faults in Fujian, and provide reliable scientific criteria for the study and classification of key danger areas of earthquakes.

As an example, we use 5 days borehole strainmeter observation data before the Wenchuan 8.0 earthquake recorded in Yushu seismic station. First, we check the reliability and stability of the borehole strainmeter through calculation of the correlation and coherent frequency between the two synthetic components S13 and S24, and find out the incoherent signal’s frequency between S₁₃ and S₂₄ as the basis for selecting wavelet parameters. Secondly, we use wavelet analysis to extract the disturbance signals in the four observation components, and calculate the time-frequency-energy distribution. Finally, we select STA/LTA trigger detection parameters according to the time-frequency-energy distribution characteristics to detect 4 observation components and 2 synthetic components respectively. The results show that the method can effectively detect the start and end time of the disturbance signal in six components, can provide timely alarm information for the daily operation and maintenance of the station operator, and provide a new method to judge earthquake precursors.

We arrange AA′ surveying line composed of circular arrays observation system and BB′ surveying line composed of linear arrays observation system, respectively, in the south and north of the proposed Linxia airport terminal in Gansu province. The results reveal that each layer is clearly visible and nearly horizontal by 2D AA′ apparent S-wave velocity profile. Geological prospecting data in relevant areas shows that the thickness of Quaternary overburden represented by loess layer is about 120 m, and the buried depth of complete bedrock surface is about 170 m. The BB′ profile shows that the inverted stratigraphic structure inclines to the south, which may be related to the layout structure of the linear arrays. Both profiles show that the continuity of each layer is good without obvious dislocation, and there should be no hidden faults and other adverse geological bodies in the site.

Based on the short arc integral approach, we recovery 40th-degree TVG-SWARM monthly time-variable gravity field for 84 months from January 2015 to December 2021 by the precision orbit data of the SWARM satellites, and compared it with the monthly gravity fields of ASU, COST-G, IGG and ITSG. The results show that: 1) In terms of the geoid degree error and the spherical harmonic coefficient error spectrum of the gravity fields, the accuracy of the low-degree spherical harmonic coefficients of different SWARM is similar, especially the first 10-degree spherical harmonic coefficients are close to that of the ITSG-GRACE/GRACE-FO. 2) The spatial distributions of global terrestrial water storage change trends between different SWARM gravity fields and the ITSG-GRACE/GRACE-FO are in good agreement. In the Amazon basin, Greenland, Mississippi river basin and western Siberia region, the trend deviation values between the TVG-SWARM and ITSG-GRACE/GRACE-FO are 0.23 cm/a, 0.27 cm/a, 0.57 cm/a and 0.47 cm/a, respectively, and the correlation coefficients between them are all above 0.85, whose results are closest to the results of IGG-SWARM. This study indicates that the TVG-SWARM has reliable accuracy and can be used to monitor large-scale changes in terrestrial water storage.

We use continuous observation data recorded by OSG superconducting gravimeter before and after the 2021 Yangbi M_S6.4 and Maduo M_S7.4 earthquakes to extract the gravity residual time series and the signal of coseismic gravity changes through harmonic analysis. The coseismic gravity changes caused by the two earthquakes at Lijiang station are calculated using the spherical dislocation theory at the same time. The results show that the observed and theoretical values of coseismic gravity change differ, the observed values of Yangbi and Maduo earthquakes are -4.37 nm/s² and 28.57 nm/s² separately, and the theoretical values are -0.19 nm/s² and 0.24 nm/s² separately. Subsequently, we analyze the gravity effects from groundwater. We find that the effect of groundwater is in the same order of magnitude as the theoretical coseismic gravity changes. Finally, we find that the magnitude of coseismic displacement jump before and after the above two earthquakes is much smaller than the magnitude of gravity change by comparing the 30-second sampling data of GPS observation in Lijiang area in the same period with the superconducting gravimeter observation, indicating that the superconducting gravimeter is affected by the pulse signal of the earthquake, leading to a significant increased drift in gravity signals during the two earthquakes.

To verify the feasibility of using portable relative gravimeters for short-term gravity tidal observations to improve the ocean tidal model, we conduct a same-site comparison at the Xiamen seismic station. Using the stational ocean tidal model corrected from FES2004 with long term gPhone data as the reference, we separate the static observation residual sequences of gPhone, CG-5 and CG-6 gravimeters. The spectrums show that the noise level(non-linear drift) of CG-5 and CG-6 at 1 CPD(circle per day) and 2 CPD are slightly higher than that of the gPhone. This indicates that the impact on the semi-diurnal and full-diurnal tides analysis is small, and the observation accuracy can meet the needs of short-time tide model correction. We built the stational tide model at Pingtan island, which is corrected from FES2014 with the data recorded by a CG-5 gravimeter. The gravity tidal load during the absolute gravity observation period 35 d ago is remeasured. In contrast with the FES2014 model, the standard deviation of group mean residual after ocean tidal correction with our stational model is reduced from 2.7 μGal to 1.8 μGal. The feasibility of CG portable relative gravimeter for tidal load observation is verified.

We investigate the background noise level, comprising instrument noise and environmental noise, based on observation data of gPhone gravimeter at China University of Geosciences(Wuhan) between 2016 and 2020, focusing on analyzing the dynamic change of background noise before and after the lockdown of Wuhan in 2020. The conclusions are as follows: 1) The noise level for gPhone gravimeter exhibits obvious seasonal variation, with the minimum noise level occurring in the alternate period of spring and summer(mid-May) and a higher noise level in autumn and winter(September to February of the next year); 2) The range of seismic noise magnitude(SNM) for gPhone gravimeter from 2016 to 2020 lies within 3.500-4.278, whereas the range of sub-seismic noise magnitude(SSNM) falls between 4.456-6.136; 3) During the lockdown period in Wuhan(January 23, 2020 to April 21, 2020), the daily SNM value decreased sharply in comparison to the corresponding period in 2019. Only after the full resumption of public transport in Wuhan on April 22, did SNM return to its previous level.

Using the observational data and global ionosphere maps provided by 2 645 stations from six CORS systems, IGS and Center for Orbit Determination in Europe, we restructure the global ionospheric electron density variations during the geomagnetic storm on September 7—8, 2017 by computerized ionospheric tomography. Further analysis finds the two ionospheric disturbance both begin about 1 h after the occurrence of the geomagnetic storm, and decrease with the recovery of the geomagnetic storm, and that there is a strong correlation between the two development trends. Ionospheric disturbance spreads all over the world. In general, the intensity at low-latitude regions is greater than that of medium-high latitude regions, the intensity of middle height region(200-400 km) is greater than that of the lower and upper layers, and the change of electron density is (3.3-9.4)×10⁵ el/cm³. There is still strong ionospheric disturbance in the low latitude area during the first geomagnetic storm recovery phase. In the recovery phase of the second magnetic storm, the ionospheric disturbance shows asymmetry in the north and south hemisphere,  the electron density in the northern hemisphere decreased, but increased in the southern hemisphere.

When multiple gross errors exist in a multi-constellation GNSS receiver, the traditional gross error detection and exclusion(FDE) method requires frequent searching to exclude potential observations, and the efficiency of excluding gross errors is low and positioning accuracy may be drastically reduced. Therefore, we propose an inertial-aided multiple gross errors detection and exclusion method. This method introduces the inertial state model and measurement model into the receiver autonomous integrity monitoring to construct the global and local test statistic to detect the outliers, excluding the wrong observations. The results show that when there are more than two gross errors in the receiver, the traditional gross error detection and exclusion method has a high rate of false detection and missing detection, and our method can significantly improve the detection efficiency and positioning accuracy.

Aiming at the problems existing in the practical application of federated filter and centralized Kalman filter as well as the problems of decreased filtering accuracy due to inaccurate statistical characteristics of measurement noise in integrated navigation, we propose an adaptive distributed filtering method of multi-sensor integrated navigation system using variational Bayesian estimation and distributed estimation. Firstly, based on the centralized Kalman filter, we derive an expression distributed filtering method which has the characteristics of optimal estimation, automatic fault isolation and no pollution to the overall navigation system. Then we propose an adaptive distributed filtering method based on variational Bayesian estimation technique, which we use to estimate the system state and time-varying measurement noise variances synchronously and in real time. Finally, we use the SINS/GNSS/CNS/ADS integrated navigation system for simulation verification. The simulation results show that this algorithm can track the abruptly or slowly varying variance of the measurement noise in real time, can effectively improve the filtering accuracy of the overall integrated navigation system and reduce the adverse effects of inaccurate statistical characteristics of the measurement noise compared with the federated filter algorithm.

We analyze the error characteristics of GPS and BDS-3 satellite broadcast ephemeris, study the compensation strategy of the inaccuracy of broadcast ephemeris, and propose a SISRE compensated undifferenced uncombined positioning model. The experiment adopts the observation data of 15 MGEX stations in 2022 for one week. The results show that when a SISRE compensated undifferenced and uncombined model is adopted, the RMS of GPS and BDS-3 static three-dimensional positioning errors are about 24 cm and 23 cm, respectively. The GPS/BDS-3 dual system combination can further improve the accuracy to about 18 cm. The RMS of GPS and BDS-3 imitation dynamic 3D positioning errors are about 73 cm and 74 cm, respectively. The GPS/BDS-3 dual system combination can further improve the accuracy to about 45 cm. The positioning accuracy of SISRE compensated undifferenced and uncombined model is equivalent to that of SISRE compensated ionosphere-free combination model.

Based on 38-view Sentinel-1 SAR images, the paper uses SBAS-InSAR technology to obtain information on the distribution, magnitude and spatial-temporal evolution of surface deformation along the Yellow river to Qingdao diversion route from 2019-02 to 2021-10. Then, we analyze the stability of the surface along the Yellow river to Qingdao diversion route based on deformation gradients, and use the Prophet model to predict the surface deformation at several characteristic points along the route. The study shows that SBAS-InSAR is able to obtain surface deformation in a large scale and long time series along the Yellow river to Qingdao diversion route and its surrounding areas, and the areas with relatively large values of linear deformation gradients in the horizontal and longitudinal profiles are highly consistent with the areas with severe surface deformation. Based on the monitoring results of SBAS-InSAR, the Prophet model is able to make better simulation and prediction for the characteristic points with small deformation.

We first verify the accuracy of water vapor products provided by the FY-4A satellite advanced geostationary radiation imager(AGRI) using radiosonde data. Then, we analyze the characteristics of water vapor anomaly changes using water vapor, land surface temperature and quantitative precipitation estimation provided by AGRI in the epicenter region of 2023-02-06 Türkiye earthquakes. The results show that: 1) The correlation coefficient between AGRI water vapor and radiosonde water vapor is 0.90, and the RMSE and mean bias are 2.51 mm and -0.06 mm respectively. 2) Prior to the earthquake, the variance of AGRI water vapor increased to 0.029~0.156 mm, with intensified fluctuations. After the earthquake, AGRI water vapor exhibited a distinct sharp rise and fall process. 3) Using the AGRI land surface temperature and quantitative precipitation estimation of AGRI data, we estimate that the reason for the water vapor anomaly may be that the increased thermal action of the ground after the earthquake caused water vapor to rise and form precipitation at the peak, resulting in a sharp drop in water vapor.

Combining BP neural network with particle swarm optimization(PSO-BP), using the data of 88 radiosonds stations in China from 2015 to 2017, taking the surface temperature, surface water vapor pressure, latitude, elevation, and day of year as the model input factors, and taking the T_m value obtained by the integration method as the learning objective, we establish the T_m model which is applicable to the China region(PSOTM). The accuracy of the PSOTM model is evaluated using the sounding data of 2018 as reference values, and compared with Bevis, GPT3, traditional BP neural network (BPTM) and general regression neural network (GRNNTM) models. The results show that the average annual RMSE of the PSOTM model is 3.08 K, which is 26.84%, 35.97%, 15.38% and 4.94% lower than that of the Bevis, GPT3, BPTM and GRNNTM models, respectively. The average annual bias of the PSOTM model is 0.32 K, which is 68.93%, 82.42% and 72.41% lower than that of the Bevis, GPT3 and BPTM models, respectively, and 37.50% higher than that of the GRNNTM model. The PSOTM model has relatively better accuracy and stability than the Bevis, GPT3 and BPTM models at different latitudes and elevations in China, and has good applicability in China.

Using wavelet transform, correlation analysis, regression analysis and other methods, we study the characteristics and mechanism of the influence of short-term air pressure disturbance on the extensometer observation at Changshu station in the time-frequency domain. The results show that the influence frequency band is mainly concentrated in 8 to 256 min; the influence of the air pressure below 8 min is weak; the correlation coefficient between extensometer measured values and air pressure and the air pressure influence coefficient of 8 to 32 min have changed from positive to negative; the average value of the correlation coefficient between extensometer measured values and air pressure above 32 min is greater than 0.7, and the air pressure influence coefficient is high and changes relatively smooth. The effect of air pressure on the NS component is about 2.5 to 3 times that of the EW component.Finally, the method of wavelet decomposition and reconstruction is used to effectively eliminate the short-time interference of air pressure.

The EW component of SS-Y tensometer at Yantai station began to show a rapid upward trend 2 days before the 2023-02-06 Türkiye M7.8 double earthquakes, and began to turn downward in the early morning of 2023-02-06, with a range of 9.58×10^-8, and maintained a rapid upward trend after the earthquakes. The stability index of Yantai tensometer is judged and it is considered that the instrument is stable. After on-site verification, no environmental interference was found. Finally, the characteristics of the earth tide distortion are analyzed, and the relationship between the distortion and the distant earthquake precursor is discussed.