There are some inaccuracies in the derivation of the sectorial harmonic term (order is equal to degree) and the quasi-sectorial harmonic term (order is equal to degree minus 1) in the related literature, and we give a strict derivation method. Based on the two derivative formulas of fnALFs, we give the standard forward column recurrence formula of its definite integration; the results are completely consistent with those given by predecessors, but the derivation process is more concise, which can be recursed from the second degree. In addition, we derive two other useful definite integration formulas of fnALFs.

This paper studies the theory and method of constructing virtual spherical harmonic of municipal geoid. First, we select the center point and radius of the build area. Then, the observed data are preprocessed, and the numerical range and location information of the observed values are statistically analyzed. Secondly, the coordinates of the observed values are transformed from geographic coordinates to spherical crown coordinates, and then to a virtual spherical coordinate system. Finally, the municipal geoid is constructed according to the virtual spherical harmonic method. The polynomial fitting, neural network and virtual spherical harmonic method are used to construct the sampling points in Nanchang city. The results show that the virtual spherical harmonic method has the smallest fitting RMS value, which is only 0.308 cm, and the best effect.

Using the geoelectric field measured by lead electrode and solid nonpolarized electrode, based on analysis of their variation characteristics, the relationship between them and regional pressure variation, and the relationship between measuring direction and nearby fault strike, we find that:1) The daily variation of geoelectric field measured by two kinds of electrodes near active fault are relatively small when they are vertical to fault strike, and relatively large when they are parallel to fault strike. 2) The geoelectric field measured by the lead electrode near the active fault has an aperiodic variation of atmospheric pressure, and the correlation between geoelectric field and atmospheric pressure in each direction is related to the angle between the measuring direction and the strike of the nearby fault. The correlation is high when the measuring direction is nearly vertical to the strike of the nearby fault, and decreases with the decline of the angles. The geoelectric field measured by solid nonpolarized electrode does not have these characteristics.

We use sparrow search algorithm (SSA) to optimize and adjust the initial weights and thresholds of the BP neural network and thus improve the accuracy and stability of the neural network model’s short-term forecast. We use the satellite clock bias data in the IGS product to compare the SSA-BP neural network model, PSO-BP neural network model, traditional BP neural network model and traditional quadratic polynomial model (QP model). The results show that the SSA-BP neural network model has the highest prediction accuracy and stability, and its superiority becomes more obvious as forecasting time increases.

We use the Bernese GNSS software version 5.2 to analyze the data of 9 years of 24 GPS reference stations in the west Antarctic region, calculating the single-day solution under the mode of double-difference processing to acquire the coordinate time series. We employ principal component analysis(PCA) and independent component analysis(ICA) to put spatial filtering on the time series and compare and analyze the filtering effects of the two methods. We use the maximum likelihood estimation method to analyze the noise characteristics before and after filtering and establish the optimal noise model for each station. The results show that both methods can effectively extract the common mode errors in the west Antarctic region, but the results of PCA are slightly better than those of ICA. The noise models of GPS stations in the west Antarctic region are diverse, and mainly for WN+FN and WN+ARMA(1). After deducing the common mode error, the optimal noise model of some stations changes, and the regional distribution characteristics are not obvious. The influence of spatial filtering on the velocity field of station is less than 0.1 mm/a, but it can reduce the order of white noise and colored noise, thus greatly reducing the uncertainty of velocity.

This paper firstly compares and analyzes the difference between the unit harmonic estimation and the multi-harmonic estimation in extracting multipath effects, introduce the mathematical principles and implementation methods of the two methods, then compare the effects of the two methods through a field experiment. The experimental results show that both unit-harmonic estimation and multi-harmonic estimation can significantly extract the multipath effect. In the case of no data interruption, the denoising effect of multi-harmonic estimation is more obvious. The rejection rate of E/N/U directions is improved by 2.67%/2.50%/4.48% respectively, but in the case of severe data interruption, the denoising effect of the unit harmonic estimation is better. The rejection rate of the unit harmonic estimation in the E/N/U direction is improved by 2.42%/4.65%/0.05% respectively.

In order to analyze the difference of data quality of the Beidou system in the Asia-Pacific region and other areas, we select the data of 10 days from 2 domestic and 3 overseas MGEX continuous tracking stations, then use Anubis software to compare and visualize the data quality of BDS and GPS systems. At the same time, we analyze the multipath effect and signal-to-noise ratio of satellites with different orbit types above C37. The results show that the data integrity rate of each BDS station is 100%. The mean value of pseudo range multipath of each frequency band and each type of satellite is lower than 52.2 cm, and the cycle slip ratio is lower than 1, except for the data of URUM station. The pseudo range single point positioning accuracy is similar to that of GPS, and in the three types of satellite orbit of BDS-3, B1I has the most serious multipath error and the lowest signal-to-noise ratio.

We use Hector software to calculate the observation data of 10 continuous stations of CMONOC of Shanxi province from 2010-11 to 2021-01. We obtain the coordinate time series of the continuous stations, and determine the optimal noise model and the corrected velocity field. The results show that: white noise (WN), flicker noise (FN) and power-law noise (PL) mainly exist in the Shanxi coordinate time series data; the optimal noise model in the North direction is WN+PL; the optimal noise model in the east and up directions are WN+FN. Taking into account the influence of colored noise, the average moving speed in the horizontal direction of CMONOC in Shanxi based on the ITRF2014 framework is 33.542 mm/a, and the moving direction is SEE 26°22′12″. The average movement speed in the vertical direction is 2.214 mm/a, showing an uplift trend.

Based on Sentinel-1A data, we use differential synthetic aperture radar interferometry (DInSAR) technology to obtain the LOS coseismic deformation field. We retrieve the geometric parameters of the seismogenic fault and fault slip distribution using Bayesian methods (BM) based on sequential Monte Carlo (SMC) sampling. The results show that the strike of seismogenic fault is about 47.810° ±2.218°, the dip angle is about 36.664°±2.499°. The epicenter location is 87.715°E, 34.365°N, and the corresponding depth is 5.673 km. The coseismic slip distribution is concentrated at a depth of 3.9~7.5 km, and the maximum slip is 0.42 m. The average rake angle is -66.598°±3.258°, which indicates that this earthquake is dominated by normal fault with slightly left-lateral strike-slip. The inverted moment magnitude is M_W5.5, slightly less than the magnitude published by the USGS.

We propose a method to identify the development mechanism of debris flow by combining the phase information and backscatter information of SAR image, so as to explore the substance source collection and instability mode of debris flow in Yizhong river of Dêqên county, Yunnan province. The spatial-temporal variation trend of soil moisture in the study area is inversed by backscatter coefficient, and the two-dimensional deformation of slope surface is obtained by using ascending and descending orbit sentinel-1A data. The results show that the soil moisture and surface deformation in the study area show periodicity and strong correlation, and the early source collection is affected by the dry-wet cycle. The soil moisture increases from January to June, and the surface soil expands under the action of high pore pressure. The surface material source is stripped and transported downward, affected by wind from July to December, supplying material source for the debris flow forming area. Using SBAS-InSAR to obtain the time series deformation of the surface reveals that the soil is unstable due to drought at the beginning of the year, later activated by rainstorm scouring. The method we propose provides a new idea for InSAR technology in the interpretation of debris flow development mechanism and has the function of early warning and prediction for debris flow disasters.

We propose a comprehensive prediction index method based on the measurement of ambient noise wave velocity to better apply the seismic data to earthquake situation tracking and short-term and imminent earthquake prediction. Using broadband continuous waveform data from January 2012 to November 2020 recorded at 5 stations in northwestern Yunnan, based on ambient noise cross-correlation and Fourier transform methods, we extract the direct Rayleigh wave travel time offset time series of day empirical Green’s function and reference empirical Green’s function of 10 station pairs. We set ±1.5 times the standard deviation as the anomaly threshold, take 6 earthquakes with M≥5.0 as samples, and use the R value scoring method to test earthquake capability of each station pair. Finally, based on the adaptive weighted comprehensive prediction method, we extract the short-term and imminent earthquake anomaly identification index(comprehensive index) suitable for northwestern Yunnan. The results show that when the comprehensive index is used for 90-day short-term and imminent prediction of 6 earthquakes with M≥5.0 occurring in northwestern Yunnan since 2012, a total of 8 abnormal indicators have occurred, of which 5 earthquakes are accurately predicted, 1 missed report, and 4 false reports. The predictive performance score R is 0.692, R₀ is 0.475. The earthquake response rate of this comprehensive index is 62.50%, and the generalization rate is 83.33%.

Based on seismic data provided by Hebei regional seismic network, we use the CAP waveform inversion method to obtain the focal mechanism of the July 12, 2020 Tangshan M_S5.1 earthquake. In order to get a more accurate focal depth, we employ the depth phase sPL fitting method to measure the focal depth. The results show the parameters of the focal mechanism solution of the mainshock are strike 143°, dip 83°, rake -14° for the nodal planeⅠ, strike 235°, dip 76°, rake -173° for the nodal plane Ⅱ, and centroid depth is 14 km. The result of the focal depth is 14 km by sPL phase method, which is the same as that measured by the methods of CAP. Combined with distribution of earthquake sequence, the seismic intensity map, tectonic setting and deep seismic reflection profiles, we conclude that the nodal plane Ⅱ is the seismogenic fault plane of this earthquake and the Tangshan-Guye fault is the control fault.

Using 1 190 local earthquake events recorded by 182 permanent stations from October 2008 to December 2017, we apply the double-difference tomography method to relocate seismic events and invert 3-D seismic velocity structure of Yishu fault zone and adjacent areas. The tomography results show that the P-wave velocity structure of Yishu fault zone has significant inhomogeneity and obvious segmentation features. The upper and middle crust of Tancheng and Juxian has low velocity anomalies. The velocity of Jiaonan block is generally lower than Luxi block. The upper and middle crust of the Taishan area in Luxi block basically shows high-velocity structures. In terms of seismicity, most earthquakes occur in low-velocity structures or transition zones between high-speed zones and low-speed zones with a depth of 5 to 20 km. The brittle rock is easy to rupture under the effect of upper mantle heat upwelling, which causes the deep stress to be transmitted to the crust, and then leads to the shallow earthquakes.

We use the regional-scale double-difference tomography method to perform a joint inversion of the source location and velocity structure of the seismic events recorded from October 2008 to April 2020 in the Haicheng-Xiuyan area of Liaoning province. After excluding the discrete travel time, a total of 5,028 seismic events are collected for positioning. We determine that the average value of the root mean square residual error of the seismic phase travel time decreases from 0.507 s before positioning to 0.279 s after positioning. The results of the relocation show: 1) Most of the earthquakes occurred 5-15 km underground, and the seismic activity in the Haicheng-Xiuyan area was more concentrated in the geological structure and distributed on the fault zone in a strip form, which is similar to the Haichenghe-Dayanghe fault. 2) The main seismic activities we obtain from the inversion are mainly distributed in the low-velocity area and the area at the junction of the high-speed body and the low-velocity body. This is related to the fault structure and deep fluid.

After a M_S6.0 earthquake occurred in Changning county, Yibin city, Sichuan province on June 17, 2019, we deployed multiple seismic monitoring instruments in Shuanghe town to obtain parameters of ground motion under different site conditions. The research results show that: 1) In the same medium, the peak acceleration of ground motion at 60 m elevation can be amplified by 1 to 3 times, and the intensity of Arias can be amplified by 2 to 5 times. At the same time, the amplification effect has certain directional advantages due to the difference of micro-topography. 2) Under the same elevation and different media conditions, the 8-9 m clay-containing gravel can magnify the peak acceleration of ground motion by up to 2 times compared with sandy mudstone, and the Arias intensity can be magnified by 3 to 5 times. 3) The overburden of avalanche deposits with a thin acceleration response spectrum has a significant amplifying effect on the short-period components of the seismic wave, and damages buildings with high stiffness and short natural vibration periods severely. 4) Houses should be located on low-altitude bedrock as much as possiblein strong earthquake mountainous areas, and building materials different from the characteristic period of the foundation should be selected to avoid resonance.

This paper introduces five new field trial observation means for Chengdu Base of China Seismic Experimental Site: High precision hydrogen experimental observation, three frequency beacon ground receiving station for electromagnetic monitoring test satellite, AETA multi-component seismic monitoring system, experimental observation of high precision optical fiber strain field detector and experimental observation of cold atom absolute gravimeter.

We use acceleration records to analyze the force state of P-wave particle, the probability distribution of random vibration of P-wave particle and its polarization phenomenon. The results show that the force vector of P-wave particle random vibration obeys three-dimensional Gaussian distribution, and its probability density diagram is elongated ellipsoid. The geometric parameters of polarization ellipsoid can be obtained by the covariance matrix of acceleration records, and the epicenter azimuth can be obtained.

To solve the short-term shortage of geomagnetic second data, we study the data of Hubei inland magnetic network and find that the data of adjacent stations have high correlation and the same trend. Based on the idea of sketch, combined with the characteristics of geomagnetism, we propose a new complement strategy that uses Fourier to fit the good data with high similarity as the contour, and adjusts the Fourier parameters to make the contour fit the default data. Then we apply the ARMA prediction model to repair the details. Through processing actual default geomagnetic data, we verify that the strategy has good repair effect and provides a new idea and method for geomagnetic second data completion strategy.

This paper introduces the structure and principle of the volumetric borehole strain meter. We analyze and calculate the thermal calibration of the instrument. We filter the data produced by the instrument with Perstev’s filtering to remove the low-frequency trend change, and obtain the M₂ wave tide factor. We correct the instrument data by the tide factor.

In order to analyze the influence of improving the sampling rate of strain observation and expanding the observation frequency band on low-frequency observation, we select the TJ-2 volume borehole strain meter to carry out comparative observations at Zhangjiakou and Huailai seismic stations. We analyze the experimental data in time and frequency domains, and summarize the relationship between the characteristics of volume strain and seismic observation frequency band.

In order to obtain the accurate and effective observation data from water tube tiltmeters for long periods, this paper studies a method of automatic water replenishment and voltage adjustment when avoiding whole-point moment, and verifies the feasibility of this method through experiments. This method not only fundamentally solves the problem caused by traditional methods on observation data, but also greatly reduces the influence of water replenishment and voltage adjustment operation. Moreover, the reliability and integrity of observation data are greatly improved.