Based on comprehensive analysis of the research of deformation precursors at home and abroad, this paper, based on the results of GPS, strain and gravity before the Wenchuan earthquake, and applying the tilt data observed around the Wenchuan earthquake, puts forward the phenomenon of ‘fixed point’, that may occur in the focal area before the earthquake. The fixed point phenomenon in crustal deformation is an important marker of the critical state of regional stress field before earthquakes, and is an important basis for the delineation of seismic risk area. With the help of the fixed point theory, the evolution of the set of deformation fixed points before Wenchuan earthquake is shown, and the deformation fixed point phenomenon before earthquakes is also explained by thin plate theory. Finally, combined with the distribution of seismic activity and the far field significant deformation anomaly, we discuss the dynamic background of the deformation fixed point phenomenon, and verify that the fixed point phenomenon of the crustal deformation before the Wenchuan earthquake is the result of the orderly movement of the stress field in the large area.

Due to the variation of amplitude of deformation observation time series, we use the least square method, the piecewise least square method based on F-test and the sliding Fourier method, to fit the annual period, respectively. The advantages, disadvantages and applicability of these three methods are analyzed by comparing the fitting residuals. The results show that they are all reasonable fitting in the case of the uniform or the gradual annual periodic amplitude. Otherwise, the piecewise least square method based on F-test, which would cause steps and discontinuous periods, is much better than the other two fitting methods.

Based on observation data of various sampling rates (10 Hz, 1 Hz and 30 s) of 19 continuous GNSS stations, this paper analyzes the impact of the nuclear explosion of Democratic People’s Republic of Korea on the crustal deformation field in northeast China. The nearest GNSS site from the nuclear explosion is JLCB. The static displacement analysis results show that the JLCB station does not show obvious co-seismic deformation, which is consistent with the results of forward modeling based on the uniform semi-infinite elastic space dislocation model. The GNSS strain results show that the principle strain has a slight adjustment in the northeast region caused by the nuclear explosion; the adjustment was within 10-8, which does not cause the variation of the surface strain in the region. The results of high frequency GNSS dynamic deformation show that this event does not cause obvious dynamic deformation at the JLCB station. In addition, the high frequency results are affected by the multipath, which may cause centimeter-level disturbance. By the method of sidereal filtering, the influence of multipath can be suppressed, and the dynamic deformation results with higher precision and better reliability can be obtained.

Based on the traditional threshold function in wavelet analysis, combined with the wavelet threshold function proposed by other scholars, this paper further studies and analyzes the practical application. We propose a new method: denoising the deformation monitoring data with a new wavelet threshold de-noising function. Theoretical analysis and examples show that the new wavelet threshold de-noising function can effectively remove noise and has good denoising effect.

Using GPS velocity field and the least square collocation method, we calculate and analyze the strain rate fields of the year 1999-2007, 2009-2013 and 2013-2016 of the area around the north-south seismic zone in China. The changing of strain rate fields and its internal reasons are analyzed. With epicenters of earthquakes that occurred from the year 2008 to 2018, the relationship between strain rates and epicenters is summarized. Finally, with geological and seismological results, we analyze the earthquake risk in the study area. As results show, in recent years, the Tibet plateau has accelerated its extension, resulting in the increasing strain rates around Qilian block and the eastern margin of Sichuan-Yunnan block; the north-eastern margin of Tibet plateau shows lateral inhomogeneous characteristics; earthquakes of MW≥6.0 are collocated with regions of highest strain rates. Earthquake risk areas can be recognized as the eastern part of Qilian mountain, Maqin-Maqu segment of east Kunlun fault, Anninghe-Xiaojiang fault zone and mid-southern segment of Honghe fault zone.

 Based on the continuous observation time series of GNSS in Yunnan since January 2018, the Kriging interpolation method is used to mesh the deformation field, the strain calculation is performed, and the surface strain is obtained. Based on baseline data, the characteristics of the regional strain field before the Tonghai M5.0 earthquake and the strain changes in the Yunnan area after the earthquake are analyzed. The results show that before the Tonghai earthquake, the overall regional strain accumulation in Yunnan has a significantly enhanced background, and a rapid reverse adjustment occurs in the short term before the earthquake. After the Tonghai earthquake, in the short-term, the squeezing strain accumulation has obviously weakened for the Dazhai-Huize areas in northeastern Yunnan and the near areas of Tengchong. There is a pressure-enhanced phenomenon in the Menghai-Mengla area of southern Yunnan.

In this paper, we manually pick the high-quality Pn-wave arrival times from the waveform data recorded at the digital seismic networks in the northwest Ordos block from 2008 to 2018, make use of the Pn velocity tomography, and we get the Pn velocity and anisotropy image in the uppermost mantle around the region. The results show that obvious lateral heterogeneities exist in the uppermost mantle of the region, which shows the close correlations to regional tectonics and earthquakes. The fast direction of anisotropy is nearly along the E-W direction around the Hetao graben. Most strong historic earthquakes in the region occur in the low velocity areas or the high-to-low velocity transition zone. These results provide important seismological clues to understand the dynamic problems related to the strong earthquakes.

In this paper, we carry out noise and non-tectonic deformation removal of GNSS vertical series by the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) and least squares method. Firstly, the ICEEMDAN method is used to decompose the GPS vertical series, and analyze the anniversary, half-anniversary and trend of the GNSS vertical series. Then, the improved wavelet threshold and permutation entropy method is used to denoise the GNSS vertical series. Finally, the least-squares method is used to fit the non-tectonic deformation series, the number of decomposition layers closest to it is found and corrected, and we obtain the GNSS vertical deformed information of noise removal and non-tectonic deformation. The results show that the ICESSDAN method can effectively remove the vertical tectonic noise of GNSS and the ICEMDAN and least squares method can improve the measurement accuracy of GNSS vertical series deformation. The RMS value is reduced by an average of 1.28 mm, and the WRMS difference increases by 0.33 mm on average.

In this paper, we introduce a data-driven RegEM algorithm into GPS coordinate time series. The interpolation effects and performances of RegEM and Lagrange method, cubic spline method and orthogonal polynomial method are compared by simulating continuous missing data of different proportions and measuring missing data respectively. The experimental results show that RegEM interpolation is superior to traditional interpolation methods in simulating continuous missing data with different proportions, and the best result is obtained in the case of continuous missing data. RegEM interpolation method has the best effect in maximizing the retention variance of the sequence with missing data, which is about 1.17 times that of orthogonal polynomial method and 1.38 times that of cubic spline method.

In the dual-antenna GNSS/MEMS integration attitude determination, MEMS accelerometer, with its low precision and low cost, usually contains relatively large noise, which results in low accuracy of accelerometers derived horizontal angles and impacts the accuracy and reliability of attitude determination. The accelerometer signal has high-frequency vibration noise caused by the inherent structure of the vehicle. Therefore, instead of the traditional time-domain denoising methods, the Butterworth low pass filter with sliding window based on frequency domain method is designed to smooth accelerometer in this paper. A vehicular test result shows that the filter has a better effect on denoising and the accuracy of accelerometers derived horizontal angles is improved by about four times, reaching (0.643°, 0.546°). Additionally, the integration attitude solution is also improved from (0.124°, 0.738°, 0.532°) to (0.122°, 0.074°, 0.052°), where horizontal angles accuracy has an improvement about one order of magnitude. It is verified that the attitude solution after Butterworth low pass filtering is more accurate and reliable.

This paper investigates the model and algorithm of the single/dual-frequency GPS/BDS/Galileo mixed double-difference relative positioning. We deduce the model and algorithm. The experiment selects zero short baseline data for testing. The positioning accuracy and ambiguity fixed speed of the GPS-only, GPS/BDS standard double difference, GPS/BDS mixed double difference, GPS/Galileo mixed double difference and GPS/BDS/Galileo mixed double difference are analyzed. Compared with the GPS-only and GPS/BDS standard double difference solution model, the experimental results show that the three-system or dual-system mixed double difference model can improve the fixed rate of ambiguity and positioning accuracy effectively.

 In this paper, we present the method of calculating zenith tropospheric delay (ZTD) from ERA5. Then the accuracy of the ZTD derived from ERA5 is evaluated using GNSS data during the entire year of 2017 with a comparison to ERA-Interim. The GNSS-derived ZTD is obtained at 26 stations in crustal movement observation network of China (CMONOC). Statistics show that the root mean square (RMS) of ZTD calculated by ERA5 is lower than ERA-Interim, indicating that the ERA5 has an obvious accuracy improvement over the ERA-Interim.

In this paper, we propose a zenith tropospheric delay interpolation algorithm based on vertical profile function by analyzing the law of zenith tropospheric total delay (ZTD) with elevation variation derived from ERA-Interim reanalysis data. Based on the vertical distribution law of ZTD, this method can realize accurate projection and extension of tropospheric delay on the elevation direction by vertical profile function. Compared with the traditional interpolation algorithm, the spatial structure malformation caused by the large elevation differences can be avoided. An experiment is performed with the tropospheric delay products of IGS, and the results show that the proposed algorithm can effectively improve the accuracy of ZTD correction value compared with the traditional algorithm. Especially in the case of elevation difference over 1 km, compared with the inverse distance weighting method, the accuracy is improved by 96%, which is 79% higher than the spatial regression method.

Aiming at solving the ill-conditioned problem caused by inadequate observation, inadequate utilization of parameter physical information and prior information in measurement data processing, this paper transforms the measurement adjustment problem into a convex quadratic programming problem by constraining the parameters with prior information, and proposes an adjustment model with spherical constraints. Based on the optimization theory and Kuhn-Tucker condition, the adjustment problem under spherical constraints is studied, and a solution method is proposed for the model. The results of numerical simulation and practical application of trilateration network show that this method has obvious better estimation in dealing with ill-conditioned problems, and can be widely used in geodetic ill-conditioned data processing.

GPS-IR is a new remote sensing technology based on satellite reflection signals. The inversion of soil moisture can be achieved by using satellite reflection signals in SNR observations. Aiming at the problem of satellite reflection signal separation, we propose a satellite reflection signal separation method based on wavelet analysis. Experiments show that wavelet analysis can make corresponding changes to the signal-to-noise ratio observations of different satellites, effectively separating satellite direct signals and obtaining more accurate satellite reflection signals. Linear regression model can well represent relative delay phase and soil moisture. The correlation between the wavelet analysis and the low-order polynomial is more obvious. Therefore, the method can be used as a new method for separating satellite reflected signals.

Zenith troposphere delay (ZTD) of GNSS ground observation stations is extracted by processing GNSS observation data during the period of severe tropical storm ‘Talas’ and tropical storm ‘Roke’. Precipitable water vapor (PWV) is inverted with ZTD. Based on the rainfall data provided by 49 meteorological stations of Hong Kong observatory, the correlation between PWV and actual rainfall is comparatively analyzed, the effects of the two typhoons on space-time distribution of water vapor in Hong Kong are also studied. The results show that PWV rises in the early stage of typhoon period and falls back after heavy rainfall; especially, PWV in the interval of successive typhoons is still higher than the level before typhoon; water vapor accumulation is the precondition of heavy rainfall, and there is a positive correlation between the cumulative time of the water vapor accumulation and the cumulative rainfall when water vapor accumulations are similar. The area with a PWV value greater than 65 mm is correlated to the typhoon grade, and typhoon path has certain influence on local water vapor distribution.

In this paper, firstly, we introduce the basic principle of the wavelet transform, discuss and analyze the influence factors of the wavelet multi-resolution decomposition and the wavelet multi-scale decomposition method, select the wavelet basic function of coif5, and propose determining the decomposition order by cross examination method. Secondly, we use this method to effectively separate the local and regional anomalies in the model test, and analyze the reconstruction anomalies qualitatively and semi-quantitatively, combining with the radial logarithmic power spectrum method. Lastly, the wavelet transform is applied to deal with the mobile gravity anomalies of differential dynamic variations of the period of 201309-201404 in the Sichuan-Yunnan region, so as to obtain the multi-scale decomposition anomalies. Furthermore, we find obvious gravity anomalies variation characteristics among D4-D6 anomalies by the wavelet transform, the reconstructed local and regional anomalies in the main earthquake location of Ludian MS6.5 and Jinggu MS6.6 earthquakes in 2014. The above anomalies are analyzed and explained in combination with the information of geological structures in this area.

In this paper, the precision of gravity field model under double precision and quadruple precision mode is compared and analyzed based on dynamics method, including the calculation of associated Legendre function, numerical integrator and gravity field inversion results. In terms of Legendre function calculation, part of the angle can be calculated in the double accuracy mode to the 1 900 order and overflow problems occur beyond this order. However, in quadruple precision mode any angle satisfies the accuracy requirement and the result is 8 orders of magnitude higher relative to the double precision mode. The quadruple precision model of numerical integrator Adams predictive correction method is 4 orders of magnitude higher than the double precision model. In terms of gravity field inversion, the inversion results of dynamic method are consistent in double and quadruple precision mode, and the accumulated geoid error calculating to order 60 is statistically 1.29×10-5 m, mainly because the linearized error of the dynamics method dominates the calculation error. The nonlinear dynamics method is 7 orders of magnitude higher than the double precision model in the quadruple precision model, and its accumulated geoid errors are respectively 8.92×10-15 m and 8.16×10-8 m.

In the same site of Jianghan basin, three different array forms: triple circular, T-shaped and L-shaped, are used for observation and comparison experiments. The results show that the dispersion curves of the three arrays are basically the same; the energy concentration degree of the three arrays is obviously different. The energy concentration degree of the triple circular arrays is the highest, and the concentration degree of the L-shaped and T-shaped arrays is also higher in the range of 2.0-4.6 Hz. Compared with the T-shaped and L-shaped arrays, the wave velocity contrast of the triple circular arrays near the stratigraphic interface is more obvious; that is, the triple circular arrays is more reliable and accurate than the other two array forms.

We systematically analyze the coseismic response characteristics to 2 earthquakes in the far field and 4 medium-strong earthquakes in the near field of the Dahekou, Zhouping, and Guojiaba wells in the Three Gorges reservoir area. Difference analysis is carried out. In addition, we compare the seismic reflection capability of these three wells with respect to seismic energy density, coseismic response amplitude and magnitude, and well seismic distance. The results show that: 1) Dahekou well has stronger reflection ability than the other two wells. 2) The coseismic response of the far-field water level of the three wells may be caused by the far-field wave triggering. The near-field coseismic response is mainly due to the regional crushing stress, and is also affected by the lithology and the fracture structure of the wellbore.