Seismic risk analysis is one of the important contents of seismological research and earthquake disaster prevention and mitigation, it has important reference values for urban planning, development of seismic standards for buildings, risk assessment and disaster mitigation public policy formulation. Seismic risk analysis includes two aspects: prediction of earthquake occurrence possibility and distribution of strong ground motion caused by earthquake rupture, where the prediction of earthquake occurrence probability or activity, which is the basis of seismic risk analysis, gives the probability of earthquake occurrence in the area of concern within a given time frame. In this paper, we briefly review the history of research from earthquake forecasting to probabilistic analysis of earthquake activity, summarize the current challenges faced, and look forward to future efforts.

We use the measured LOD values of EOP 14 C04 from 1984 to 2022 released by the International Earth Rotation and Reference Systems Service(IERS) for spectrum analysis and period item extraction. We then use the method of least square extrapolation model combined with polynomial curve model to apply the extracted period term to the fitting of LOD sequence. The experimental results show that, compared with the single LS extrapolation model fitting, the RMSE of the fitting sequence decreases from 0.000 3 seconds to 0.000 1 seconds. The deterministic coefficient is increased from 0.8 to 0.97 by the new method. These results can provide reference for the prediction of LOD sequence.

Aiming at the problem of noise accumulation in deep learning model errors of orbital error sequence data, we propose an EEMD-LSTM combined prediction model and perform orbit prediction analysis with three types of satellite data: GEO, IGSO and MEO. The results show that the EEMD-LSTM combined prediction model can suppress the error accumulation of noise in satellite orbit forecasting, improve the accuracy of GEO, IGSO and MEO satellite orbit prediction, and fit the orbit prediction error of dynamic model well, and the average improvement rate(imp) of EEMD-LSTM combined prediction model for GEO, IGSO and MEO satellites increases by 2.70 percent point, 2.46 percent point and 8.33 percent point, respectively.

This paper analyzes the characteristics of the inter-system bias(ISB) parameters of Beidou-2(BDS-2) B1I/B3I and Beidou-3(BDS-3) B1I/B3I, B1C/B2a signals. It then evaluates BDS-2/BDS-3 static and kinematic precise point positioning(PPP) performance when using B1I/B3I and B1C/B2a signals alone. The experimental results show that the ISB parameters between BDS-2 and BDS-3 B1C/B2a signals are greater than those of B1I/B3I signals, and both have better intra-day and inter-day stability. Compared with single BDS-2, the combination of BDS-2 and BDS-3 can significantly improve the positioning performance of static and kinematic PPP, the convergence time is shortened by more than 51.9%, and the positioning accuracy is improved by more than 46.1%. Compared to B1I/B3I signal, the convergence time of PPP is shortened when the BDS-3 B1C/B2a signal participates in the PPP solution. When the BDS-2/BDS-3 ISB parameters are estimated, the PPP convergence time in static and kinematic modes is shortened by 8.8% and 12.6%, respectively, and the positioning accuracy is improved by 7.1%.

The continuous GPS reference station data of the Chinese Continental Tectonic Environment Monitoring Network are used to reveal the spatial distribution characteristics of the amplitude and phase of the vertical period. The results show that the vertical period signal of each station exhibits obvious seasonal variations, the average amplitude of the semi-annual period signal is only 1/4 of that of the annual period signal, and shows different spatial distributions. The amplitude of the annual cycle signal gradually decreases from west to east in space, with smaller amplitude in southeast coastal areas and larger amplitude in Sichuan and Yunnan; the amplitude of the semiannual cycle gradually decreases from southwest to northeast, and the semiannual cycle phenomenon is more obvious in north China and Sichuan and Yunnan. There is a big difference between phases of annual cycle and semi-annual cycle signals; the peak of annual cycle signal appears between February and August, and the peak of semi-annual cycle signal mostly appears in January and May, and there are obvious zoning characteristics. The peak of the annual cycle signal gradually appears later with increasing latitude, and the peak of the annual cycle signal appears later in coastal areas than inland at the same latitude; the peak of the semi-annual cycle signal appears mostly in May in southwest, northeast, and north China, and in January in south, central and northwest China.

To evaluate the receiver measurement noise of the new signals B1C and B2a of BDS-3 in kinematic mode, we determine the measurement noises of the new signals by zero-baseline kinematic test and compare the results with other GNSS signals. Meanwhile, we compare the kinematic results with the static mode. In the kinematic test, the RMS values of pseudorange noises of MEO satellites on B1C and B2a frequencies of BDS-3 are 8 cm and 4 cm, respectively, and the carrier phases are 0.061 cm and 0.082 cm, respectively. The measurement noise of IGSO satellites increases slightly. The pseudorange noise of each frequency of the four constellations are obviously different, but the phase noises range is not large. Although there is a decline in kinematic observation data quality, the overall pseudorange noises on B1C and B2a frequencies are not significantly different compared to static noises. However, the difference of the carrier phase noises is more significant.

To overcome the problem that the accuracy of polynomial model decays quickly during the period of rapid satellite frequency variation, we develop a new prediction model based on LSTM neural network. The experimental results show that when the satellite clock is running normally and smoothly, the results of these two models are almost identical. When the output frequency of satellite clock changes rapidly, the prediction accuracy of LSTM neural network model is significantly better than that of polynomial model, and it can still provide high precision forecast results of clock offset.

To study the evolution of tropospheric delay during typhoons, based on ERA5 reanalysis data, this paper calculates atmospheric precipitable water vapor of each altitude layer and tropospheric delay during northwestern Pacific typhoon 1822 Mangkhut, 1622 Haima and northwestern Atlantic hurricane(typhoon) 1709 Irma. The results show that there are spatial and temporal differences between the tropospheric delay calculated by ERA5 data and IGS tropospheric delay product. The stronger the influence of typhoon on the station, the more consistency is affected. Further analysis shows that typhoon transits change the precipitable water vapor and its proportion in each altitude layer at the same time, both affecting tropospheric delay. The former is dominant. At a certain amount of precipitable water, the tropospheric delay is the largest when the proportion of water vapor between 850-500 hPa is the largest. Typhoons increase the amount of water vapor distributed in the lower troposphere, so the estimation of tropospheric delay using the traditional tropospheric delay model may produce additional errors.

 We collect the data of near-field intensive GNSS stations in Nepal, and use GAMIT/GLOBK software to calculate the data of 58 near-field continuous GNSS stations and 41 post-earthquake mobile GNSS stations in Nepal from 2011 to 2017. We analyze and process the periodicity, common mode error and noise of GNSS time series. The results show that: 1) The average WRMS of E, N and U components decreased by 15.52%, 26.41% and 45.06% after GRACE corrected the period term of GNSS time series; 2) In view of the large number of missing data in the time series, the traditional PCA method is improved to calculate the common mode error by using the first principal component, and the efficiency of the three components reached 61.91%, 53.91% and 53.88%, respectively; 3) Noise analysis shows that the optimal noise model of the Nepal earthquake near field GNSS station is WN+FN; compared with the WN model alone, the WN+FN model underestimates interseismic velocity, coseismic displacement and post-seismic displacement by about 6 to 9 times, 4 to 7 times and 2 to 4 times, respectively. The results of this paper are of great significance for the maintenance of regional coordinate frame, and the inversion of geophysical model of co-seismic rupture and post-earthquake residual slip of Nepal earthquake.

We use GPS observations from 1999 to 2021 to study the crustal deformation characteristics in the area near the epicenter of the 2022 Menyuan 6.9 magnitude earthquake. The velocity field shows an obvious characteristic of ‘big in the south and small in the north’ on both sides of the Qilianshan-Haiyuan seismic belt. The results of the velocity profile of the seismogenic fault show that the extrusion rate on both sides of the fault is 3.1 mm/a, the strike-slip rate is 3.9 mm/a. These results are consistent with the strike-slip-dominated focal mechanism solution. This earthquake is in the gradient zone, which transitions from the high-value area to the low-value area of the principal strain rate field and surface expansion rate field. The earthquake occurred at the edge of the high value area of the maximum shear strain rate field and the second tensor invariant of strain rate. The coseismic Coulomb stress triggers most of the aftershocks and has a certain stress loading effect at the area from the Lenglongling fault to the Haiyuan fault. Based on the analysis results of crustal deformation characteristics and Coulomb stress, we think that the seismic risk of the area from the Lenglongling fault to the Haiyuan fault has been certainly improved.

Based on discontinuous deformation analysis(DDA), we take an area from the Jiali fault region as an example to explore the changes of geostress distribution during the fault creep process. The results show that: the fault creep may lead to a significant increase of stress in rock mass and the stress has a similar trend with the increase of depth; the stress in fault fracture zones is lower than that in the surrounding rocks on both sides in general; the fault creep can cause the development of a large number of cracks in rock mass, resulting in the discontinuity of stress distribution; the areas of stress concentration in fault fracture zones and the surrounding rocks on both sides show the same distribution at different depths.

We undertake dense observation of Fuling Jiaoshi area, Chongqing, for a period of 1 a by setting up mobile stations to understand the characteristics of seismicity in this area. We explore the genetic mechanism of microseisms and the reasons of significant differences in seismicity between others shale gas reservoirs in Sichuan basin. The results show obvious microseisms in this area. The relocated microseisms are mainly distributed in clusters along multiple faults on the boundary of the exploitation area and are concentrated near the peripheral faults on the southeast side of the exploitation area. The dominant focal depth of earthquakes is 2—6 km. We infer that the seismic activity in this area may be related to the localized disturbance on the boundary fault caused by industrial activities and the seismic disaster risk in this area is relatively small due to the direction of stress field, stress magnitude and tectonic characteristics.

We study the attenuation of coda waves and its frequency and lapse-time dependence based on Aki Model in Xiangjiaba and Xiluodu reservoirs region. We analyze coda waves from 99 earthquakes recorded in this region. The magnitudes of the analyzed events range from 2.1 to 4.1. The Q_c values show strong frequency dependence, Q(f)=(120.8±3.6)f(0.771 2±0.010 3). Our results provide a good basis for the calculation of seismic source parameters. Compared with Koyna reservoir, Aswan reservoir and Xinfengjiang reservoir, Xiangjiaba and Xiluodu reservoirs are characterized by high Q₀ value and low n value, which are consistent with the seismic activity of reservoir areas.

We apply the finite power terrain correction method(i.e., the Tesseroid forward modelling in harmonic spectral domain) to the gravity gradient calculation in terms of lunar topography. Using gravity data from the Gravity Recovery and Interior Laboratory(GRAIL) mission and terrain information recovered from the Moontopo720 model, we calculate the total gravity tensors anomaly after terrain correction at the height of GRAIL satellite. By taking advantage of the multi-component characteristics of gravity gradient and the relevant experimental results, we estimate the spatial horizontal range distributions of underground mascons through the horizontal gradient anomaly. Using the total gravity gradient anomaly maps, we preliminarily verify the distributions of main fault structures caused by tidal gravity.

We use the ITSG-Grace2018 daily gravity field solutions model to invert the changes of terrestrial water storage(TWS) in Chongqing from January 1, 2003, to August 31, 2016. We compare the model with hydrological data(WGHM, GLDAS) and precipitation data(CPC). The flood events from July 16 to 18, 2007, July 2 to 5, and July 8 to 13, 2012 in Chongqing are our focus. The results show that TWS derived from ITSG-Grace2018 is in good agreement with that from WGHM and GLDAS. The correlation coefficient between ITSG-Grace2018 water storage change and precipitation anomaly is 0.50, indicating precipitation is an important factor leading to TWS changes in Chongqing. For flood disasters shorter than one month, the monthly solution cannot give the spatio-temporal evolution process before and after flood, while the daily solutions can reflect more high-frequency details, but there is a time delay compared with the precipitation data.

We select the seismic catalog of Tengchong area in Yunnan province from 2009 to 2019, and use the Schuster test method to analyze the distribution characteristics of tidal phase angle of seismic activity. Combined with the corresponding relationship between seismic activity and lunar phase in 2019, we explore the possible relationship between seismic activity and astronomical tidal stress in Tengchong area. The results show a dominant tidal phase angle at the time when the earthquake occurred, with the P value far less than 5%. The occurrence time of seismic activity in 2019 also shows a certain correspondence with lunar phase; the lunar phase effect is more obvious when moderate and strong earthquakes occur. Both statistical tests reveal that there is a certain correlation between seismic activity and astronomical tide in Tengchong area; mainly shallower seismic activity is modulated by astronomical tides.

By processing the observation data of 50 mobile geomagnetic vector survey points in Shandong and its surrounding areas from 2018 to 2020, we obtain the variation characteristics of lithospheric magnetic field in two consecutive periods from April 2018 to April 2019 and April 2019 to April 2020. The results show that the horizontal and vertical vectors in the two periods have obvious local anomaly characteristics near the epicenter of Changqing M4.1 earthquake; the anomaly may appear nearly 2 a before the earthquake. The amplitude of horizontal vector near the epicenter of the previous period is relatively high, the direction turns in the near field and is relatively consistent, the amplitude of vertical vector is also high, and reversal occurs near the epicenter. In the later stage, the horizontal vector direction near the epicenter converges and the energy weakens, the amplitude of the vertical vector is also low, and the direction is reversed near the epicenter. The abnormal energy is first strong and then weak, which may be related to the phased change of stress state in the earthquake area.

To study the output characteristics of the variable area cylindrical capacitive inclination sensor considering the edge effect, this paper combines the conformal transformation method, Green’s function method and computer numerical simulation to discuss the electric field of the variable area cylindrical capacitive inclination sensor, give the expression of its capacitance, draw the variation curve of the sensor capacitance with the inclination, and analyze the factors affecting the linearity and sensitivity of the sensor. It points out how to improve the output characteristics of the sensor. The numerical simulation results show that when the center angle of the outer plate of the sensor is smaller than that of the inner plate, reducing the distance between the two plates can increase sensor linearity and sensitivity at the same time. Because the lateral edge effect of the sensor plate is considered in this paper, the results obtained have high accuracy.

We propose an improved wavelet threshold de-noising algorithm combined with adaptive noise complete set empirical mode decomposition(CEEMDAN) for the de-noising of groundwater temperature observation data. After using this method and the traditional denoising method to denoise the simulation signal respectively, we find that the proposed denoising method has better performance, and shows better effects than the traditional single filtering method in processing the actually collected groundwater temperature data containing noise and abnormal mutation.