To suppress the sea clutter in delay Doppler map (DDM) and improve the accuracy of sea surface target inversion, we propose principal components analysis (PCA). In this paper, the Norwegian Snøhvit gas platform is used as the sea surface target, and the DDM data on November 13, 2016, are used for target inversion. Before using PCA to suppress sea clutter, the average error of inversion position is 17.65 km, the average error of inversion position after suppressing sea clutter is 11.42 km, and the position accuracy is improved by 35.30%.

Based on the SNR(signal-to-noise ratio) data of doy 268-366 at the MAYG station on the east coast of Africa in 2020, we carry out the GNSS-IR(global navigation satellite system interferometric reflectometry) sea level monitoring study. We compare the results with the measured tide level of Dzaoudzi tide gauge station. The experimental results show that BDS-GEO is not suitable for shore-based altimetry. The monitoring accuracy of BDS-MEO is better than that of BDS-IGSO and GPS.

We systematically compare the differences between the modeled attitude and nominal attitude derived by the published yaw attitude models for BDS-3 SECM and CAST MEOs during deep eclipse seasons, and evaluate its influence on the calculation of antenna phase wind-up and phase center offsets(PCO) and PPP performance for the first time. The research shows that, for BDS-3 MEOs during maneuvers, adopting nominal attitude will cause the PCO correction errors for CAST and SECM satellites to reach 0.2 m and 0.02 m, respectively, and the wind-up correction errors to reach 0.1-0.2 cycles. Due to the shorter duration of satellite maneuvers and stronger geometric strength, compared with the modeled attitude, the use of the nominal attitude will not cause a significant drop in the PPP results.

To improve the denoising effect of GNSS height time series, we decompose the simulation signal and height time series of Lhasa station from 2000 to 2020 into several intrinsic mode functions(IMF) by complete ensemble empirical mode decomposition with adaptive noise(CEEMDAN) method respectively. We perform wavelet packet multi-threshold decomposition for each IMF component, select different threshold criteria according to the percentage of the energy of different nodes in the total energy of the IMF, reconstruct the noise-reduced node to obtain the noise-reduced IMF component, and then obtain the noise-reduced time sequence. By the indexes of signal-to-noise ratio and root mean square error, we compare and analyze the denoising effect of the proposed method, EMD, CEEMDAN, wavelet denoising and wavelet packet multi-threshold denoising. The results show that the proposed method has the best effect.

To address the issue of the complementary ensemble empirical mode decomposition(CEEMD) having to set screening criteria, this paper takes seasonal signals into consideration when using CEEMD to denoise GNSS coordinate time series. The improved method firstly deconstructs GNSS coordinate time series into numerous intrinsic mode function(IMF), calculates their average periods, then utilizes IMFs with an average period of less than 120 days as noise components, while reconstructing the remaining components as signal components. This study applies the method to denoise 227 GNSS vertical coordinate time series stations over mainland China; it compares the results of CEEMD with the continuous mean square error and correlation coefficient methods. The results indicate that the described method does not denoise excessively, whereas the other two methods do.  At the stations without excessive noise reduction, the average correction rates of RMS, power law noise, and velocity uncertainty of the GNSS coordinate time series of our methed are 19.13%, 88.29% and 86.46%, which are better than the other two methods.

We analyze the feasibility of GNSS ZTD instead of GNSS PWV using the GNSS continuous observations provided by CMONOC, and analyze the GNSS ZTD response to the super eastern Pacific El Niño(EP-El Niño) by fast Fourier transform and wavelet transform. The results show that the super EP-El Nio event will increase the PWV content in Chinese mainland(the response is more significant in the tropical monsoon zone and subtropical monsoon zone), weaken the 9-month significant period of GNSS ZTD, and increase the significant period within 0.8-3 months.

By processing the observation data of the GNSS reference station near the epicenter of the M_S6.4 earthquake in Yangbi, Yunnan on May 21, 2021, three days before and after the earthquake, we analyze the impact of the earthquake on the coordinate stability of the reference station in a short period of time. According to the dynamic PPP and high-precision static data processing results, the analysis shows that the area near the epicenter of the Yangbi earthquake have significant displacements towards the southeast, the maximum displacement of the stations is about 4.8 cm, showing the characteristics of right-handed strike slip movement.

We use the composite source model to simulate the strong ground motion of the 2017 Jiuzhaigou M_S7.0 earthquake, generating a specific circular subevent distribution with kinematic model of fault rupture. After parameter sensitivity analysis of seismic moment, stress drop, rupture velocity, sub-fault size and focal depth, we obtain a set of reasonable focal parameters. Based on the composite source model, we calculate the ground motion in this area, comparing it with observed data such as peak ground acceleration(PGA), response spectrum and PGA distribution characteristics. The results of simulations show that the calculated ground motion waveform is very close to the observed data. This verifies the validity of the composite source model in calculating strong ground motion; the sensitivity law also provides a basis for the composite source model to calculate the change interval of ground motion parameters in areas lacking strong motion records.

By arranging slope seismic monitoring instruments in Wutong village, Gongxian county, Yibin, we collect data from the Xingwen county M_S3.1, Gongxian M_S4.5 and Changning county M_S4.6 earthquakes. We filter and correct the seismic response data of Gongxian aftershocks collected at 1^#, 2^# monitoring points on the monitoring profile, and the magnitude, elevation after the seismic response caused by azimuth and other factors to the slope. We infer that: 1) the distance between the half wavelength of the local seismic wave and some specific parts of the mountain is close, the slope terrain and the wave crest of the seismic wave are coupled, and the topographic amplification effect is significant, up to 2.765 times of the reference point. Here, the mountain is more likely to produce large-scale shaking, which is more likely to cause mountain geological disasters. 2) Through the analysis of the Gongxian M_S4.5 and Changning county M_S4.6 earthquakes, we infer that when the seismic wave propagates along special parts(such as ridge, etc), the seismic acceleration and arias intensity are more significant. 3) Through the analysis of the change of seismic acceleration of seismic data, we conclude that under the action of seismic load, the acceleration response of slope increases with increased magnitude. 4) With the change of elevation and magnitude, the seismic acceleration and arias intensity of monitoring points also change, and we conclude that elevation and magnitude have amplification effect on the seismic response of slope. 5) Under the coupling effect of elevation and micro landform, the seismic acceleration also has obvious amplification effect.

Using GPS continuous observation data from the CORS network of Qinghai province, we obtain the coseismic deformation field and the state of surface movement during the 2021 Maduo M_W7.4 earthquake. The results reveal that the near-field stations on the south and north sides of the fault show southeast and northwest movements respectively, which is consistent with the left-lateral strike-slip mechanism. The coseismic permanent deformation is concentrated within 300 km of the epicenter. The sites within epicentral distance of 150 km captured centimeter-level displacements; the maximum horizontal displacement is 28.3 cm, occurring at the JDUO station. The permanent displacement extracted by the high-rate GPS kinematic deformation is approximately equivalent to the static calculation result, and the maximum peak value of the deformation waveform is 49.9 cm, which occurred at the KANQ station. Based on the epicenter distance and the initial motion time of the waveform, the estimated seismic wave velocity is 2.8-4.9 km/s. The estimated velocity at the eastern end of the fault is higher than that of other sites, which may be related to the directionality or the propagation velocity of the rupture. According to the empirical formula of magnitude, the estimated magnitudes of the deformation waveforms are in the range of M6.8-7.6, and the fitted average magnitude is M7.35±0.15. If data were processed real time, the robust magnitude could be derived within 70 s after the rupture initiated.

This study constructs a multi-scale spherical wavelet model of regional crustal deformation in the southeastern margin of the Qinghai-Tibet plateau based on the high-precision GNSS monitoring data from 1999 to 2007 and 2011 to 2017, by fully considering the actual non-uniform distribution of GNSS stations. We quantitatively analyze the variations of current crustal deformation and crustal strain rates at different spatial scales before and after the Wenchuan strong earthquake. The results show that the overall crustal movement in the study area has inherited development characteristics before and after the Wenchuan strong earthquake. Obvious gradient zones of speed differences are formed at the Longmenshan, Anninghe, Zemuhe and Xiaojiang faults, and the high strain rates are mainly concentrated in the above main faults and nearby areas; after the Wenchuan strong earthquake, the overall crustal movement velocity of the study area, especially the GNSS velocity value on the northwest side of the Longmenshan fault zone increased significantly, and the Qiangtang, Bayan Har and Sichuan-Yunnan blocks also show a trend of accelerating the migration to southeastward and promoting the south China block; the strain rate fields at different scales reflect the characteristics of strain accumulation in different spatial ranges. The results of the scale factor q=7 in the southeastern margin of the Qinghai-Tibet plateau are reasonable (the reasonable maximum scale factor); when the scale factor q=6, it can better reveal the characteristics of regional overall tectonic activity, that is, it can clearly reveal the significant high values of principal compressive strain, surface compression and maximum shear strain rate at Longmenshan fault zone after the Wenchuan strong earthquake; when the scale factor q=3-7 (the best combined scale factor), the large-scale (overall) and local deformation characteristics of regional crustal movement can be comprehensively revealed. After the Wenchuan earthquake, the main fault zone in the study area, especially the epicenter and its vicinity, has significantly increased seismic activity.

A new method for paleo-landslide deformation prediction is proposed. Firstly, the paleo-landslide deformation data are decomposed by ensemble empirical mode decomposition(EEMD) and singular value decomposition(SVD), and then the deformation of the resurrected area of the paleo-landslide is predicted by the component combined neural network. Finally, the multi-fractal detrended fluctuation analysis(MF-DFA) is used to evaluate the multi-scale trend of the ancient landslide. Taking Wangjiapo landslide as an example, the effectiveness of the proposed method is analyzed.The results show that the combined decomposition model EEMD-SVD has stronger data decomposition ability than the single decomposition model which can effectively realize the information decomposition of landslide deformation data. The sub item combination prediction model based on neural network is suitable for landslide deformation prediction. The relative error of the prediction results is mostly about 2%, with high prediction accuracy. The extrapolation prediction shows that the landslide deformation will increase further, with an increase rate of 1.23-1.36 mm/cycle.Through the multi-scale feature analysis of MF-DFA model, we concluded that the landslide deformation has multifractal characteristics, and the deformation tends to increase, which is consistent with the prediction results, and proves the accuracy of the above prediction results.

Moderate to strong earthquakes occur frequently in Keping block. To obtain more judgement basis of earthquakes, based on the earthquake data recorded by Xinjiang Digital Seismic Network, we calculate the apparent stress of M_L≥3.0 earthquakes occurred in Keping block from 2010 to 2020. We discuss the scaling relationship of source parameters and analyze the temporal-spatial variations characteristics of apparent stress before and after M≥5.0 earthquakes and Jiashi M_S6.4 earthquake. The results show that the apparent stress is positively correlated with magnitude. The apparent stress values show different degrees of temporal and spatial high anomalies before M≥5.0 earthquakes in Keping block. The Jiashi M_S6.4 earthquake occurred in the process of high apparent stress, there was an abnormal area of high apparent stress in the epicenter area five months before the earthquake.

We collect 371 focal mechanism solutions in northeastern Tibetan plateau and its surrounding areas, and carry out a grid 1°×1° tectonic stress field inversion. The results show that the maximum principal compressive stress on the inner edge of the northeastern Tibetan plateau is mainly NE, and the maximum principal compressive stress on the outer edge shows the characteristics of clockwise rotation from west to east, that is, the axis of the maximum principal compressive stress changes from near NNE in the west to NE in the middle, and then from NE in the middle to NWW in the east. From the perspective of different depths, the northeastern Tibetan plateau is calculated by 2°×2° stress field inversion. The results show that there is a huge difference in the fault system between the upper and lower parts of the crust, and the reason for this difference may be related to the compressive thickening of the crust.

We use C⁺⁺ to apply an inversion method for source rupture of earthquakes on Qt platform based on QSSP software. The algorithm is divided into two stages. The first stage is a global search by heat bath algorithm, which consists of two steps. First, we divide the parameter range according to the initial conditions such as the tectonic background of the fault area. Second, we define random parameters at each range and start the iteration for making the preliminary waveform fitting avoid the local optimal solution. The second stage is a fast convergency by quasi-Newton algorithm, which improves the fitting level of waveform. In this stage, the iteration will stop until the result of objective function is less than the error, and output fits undetermined parameters. In this paper, to avoid the parameter ill-posed problem, we use the Laplace equation to establish the smoothing matrix, and the smoothing factor is introduced to smooth constraint on the fault model. In addition, we use checkerboard model to ensure the stability and reliability of the above method. At last, we reverse the rupture process of the Lushan M_S7.0 earthquake on April 20, 2013 using gravity data from 13 gravity stations, and compare with other research.

From the seismic observation report from 2008 to 2021, we extract the travel time data of direct P and S waves of small earthquakes near Badong area. We calculate the wave velocity ratio by the Wadati method of single earthquake and multi-station and single station and multi-earthquake, respectively. We analyze the temporal and spatial evolution characteristics of wave velocity ratio before and after the Badong M_S5.1 earthquake in 2013. We conclude: 1) the wave velocity ratio of 8 stations on the east and west sides of the epicenter before the Badong earthquake changed abnormally in varying degrees with decline-rising process. 2) The wave velocity ratio of multiple stations in the surrounding area of Badong earthquake experienced the change process of two years decline-two years rise before the earthquake, which is similar to the result of single station wave velocity ratio. 3) The spatial evolution images of the Wadati method of single earthquake and multi-station show that the low value of wave velocity ratio in the first two years of Badong earthquake are concentrated around the epicenter, and the wave velocity ratio rises to the high value after the earthquake.

Based on seismic data waveform recorded by Inner Mongolia Seismic Network from 2010 to 2020, we select 3 010 Pg waves and 3 410 Sg waves of 391 earthquakes from 24 fixed stations. Using double-difference tomography, we inverse the three-dimensional velocity structures of Pg- and Sg-wave in the crust on the northern margin of the Ordos block, and relocate all earthquakes in this area. The results show that at 5-15 km depth, there is a large continuous high-speed body in the eastern study area, while the southwest shows the distribution characteristics of relatively low speed. Most earthquakes are concentrated in the transition area between high and low speed areas, which also reflects the vulnerability of crustal media in the study area. At 20-30 km depth, the high-speed area spreads westward with the increase of depth. It is connected to the high-speed area of Hubao basin, indicating that a tectonic body crosses the crust of Hubao basin.

Using GPS data and ERA5 temperature data from the European Centre for Mesoscale Weather Forecasts(ECMWF), we extract the temperature anomalies and ionospheric VTEC anomalies before the November 13, 2016 Kaikoura, New Zealand M_W7.8 earthquake. We then discuss the spatio-temporal characteristics of atmospheric disturbances before the earthquake. The results show that there were temperature anomalies and ionospheric VTEC anomalies north of the epicenter on November 8 and 9, 2016, respectively. The temperature anomalies have the characteristics of temperature-strengthening, temperature-attenuation, temperature-peak, temperature-rapid decay, which are basically consistent with the heat release process of rock deformation-fracture. With increasing height, the area and amplitude of temperature increase gradually decrease, consistently with the trend of seismic thermal anomalies gradually subsiding in the process of bottom-up uplift.

We analyze the accuracy of the RT-GIM products during January and August 2021 from Chinese Academy of Sciences(CAS), Centre National d’Etudes Spatiales(CNES), Canadian Geodetic Survey of Natural Resources Canada(NRCan) and Polytechnic University of Catalonia(UPC). Compared to the post-processed IGS-GIM, the RMS between those RT-GIM and the IGS-GIM is 3.93 TECu for CAS, 4.01 TECu for CNES, 4.50 TECu for NRCan and 3.86 TECu for UPC. Compared to the dSTEC derived from reference stations, the STD of RT-GIM from CAS, CNES, NRCan and UPC are 4.42 TECu, 4.40 TECu, 4.96 TECu and 4.42 TECu, respectively. Based on the positioning results carried on 21 globally distributed GNSS stations during 7 consecutive days, we analyze the 95% quantile of vertical residuals to check the positioning improvement of different RT-GIM. Compared to positioning results corrected by the broadcast ionospheric model, the positioning accuracy increases by 11.9% for CAS, 18.3% for CNES, 3.4% for NRCan and 15.5% for UPC in the elevation direction of the northern hemisphere.