15 May 2019, Volume 39 Issue 5
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jgg. 2019, 39(5): 441-446.
We collect multi-period precision leveling data from the 1970s in central-southern Shaanxi and obtain the vertical velocity field of the area using the dynamic adjustment method based on GPS vertical velocity constraints. The result shows that the vertical movement of the crust is generally mountainous, the plateau relatively rises, and the basin’s relative subsidence. Relative to the Guanzhong basin, the rate of its rise in the west of Qinling mountains and Longshan in the west is 4~5 mm/a, that of the north Qinling orogenic belt is 2~3 mm/a, and that of the Ordos in the northern part of the basin is 3~4 mm/a. The subsidence rates of north Qinling and the north Dabashan rift at Ankang are about 1 mm/a and 2.0 mm/a, respectively. The vertical slip rate of the northern margin of Qinling fault is 1.3~1.8 mm/a, the frontal fault of Huashan is 2.0~2.8 mm/a, the Weihe fault is less than 1.0 mm/a, the northern margin fault of Weihe basin is 1.0~2.5 mm/a, while the southern faults of are 0.7~1.1 mm/a.
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jgg. 2019, 39(5): 447-451.
Combined with error probability statistics, this paper compares two main methods for calculating RMS value and gives the distribution of error probability. The results show that the result error for RMS calculated from waveform filtered by FIR bandpass filter is mostly dependent on the types of window function and filter order, with filter order playing a more import role. In addition, the error probability of RMS calculated from PSD depends on the parameter combinations of window function type, window length, and overlap ratio related to the pwelch function, mainly on the window length, and will reach a steady status with a certain number of sample waveforms. The distribution of error probability indicates that the second method is better than the first.
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jgg. 2019, 39(5): 452-457.
A MS7.0 earthquake occurred in Jiuzhaigou, Sichuan, on August 8, 2017. In order to improve the precision of the InSAR coseismic deformation field of the earthquake and to clarify the structural morphology and formation mechanism of the seismogenic fault, the coherence coefficient of the deformation zone is statistically analyzed to determine the coherence threshold. Atmospheric correction of the deformation field is performed by GACOS(general atmospheric correction on-line service). Then, the basic shape of the seismogenic fault is confirmed according to aftershock distribution and geological background. Finally, the slip distribution of the seismogenic fault is inverted based on the Okada elastic half-space dislocation model. The corrected InSAR coseismic deformation field shows that the maximum sink is 25 cm and the maximum lift is 10 cm in LOS, which are respectively located in the northwest and the southeast of the epicenter. The long axis of deformation is in NE direction and the main deformation zone is located on the west of the seismogenic fault. The inversion results show that the RMSE of the corrected InSAR deformation field is smaller than that before correction. The maximum slip amount is 0.9 m, the average slip angle is -0.5° and the moment magnitude is MW6.5. The rupture is mainly concentrated in the range of 1 ~ 20 km underground. The results are consistent with the results of USGS and GCMT. The consequences indicate that using GACOS to correct the InSAR coseismic deformation field of Jiuzhaigou has some effect on improving the accuracy of the deformation field, but the inversion result of fault slip distribution is not significantly different than before correction. The attributes of the seismogenic fault are basically consistent with the properties of the northern segment of the Huya fault. Combined with the results of the aftershock repositioning, it can be inferred that the seismogenic fault is the northern extension of the Huya fault. The earthquake event is the result of the collision between the southeast torsion of Bayankala block and the South China block. The difference distribution of viscous lower crust is the main reason for the change of the slope angle of the Huya fault.
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jgg. 2019, 39(5): 458-463.
Using finite element method on the southeast margin of the Tibetan plateau, this paper establishes a more detailed and accurate three dimensional finite element model of elastic, selects the stress of the nine different boundary conditions, applies optimization analysis for each project in post-processing, analyzes the corresponding station deformation GPS simulated values and measured error, and finally chooses the best solution as palaeotectonic stress field. Results show that around four million years ago the ancient stress field of the southeast margin of Tibetan plateau mainly originated from intense collision of the Indian plate NNE with the Chinese mainland plate. The mainland of China, especially the Tibetan plateau in southwest region, is the main power source of the tectonic stress field, and controls how the various blocks interact and their motion patterns. The paleostress field on the southeastern edge of the Tibet plateau mainly includes the following sources: The NE-WS directional stress in the southwest is about 70 MPa directly from the Indian plate. Southern NS force 33 MPa; lateral NW-SE blocking force of southeast Yangtze block is 56 MPa. At the same time, the strong EW blocking force of the Yangtze block in the eastern north is 90 MPa, and these forces act together on the southeastern edge of the Tibetan plateau, forming a complex stress field.
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jgg. 2019, 39(5): 464-468.
This paper uses the horizontal GPS velocity field of the Chinese continent in 1998～2007 and 2009～2017 years as constraints. Based on the block-dislocation model, we study the movement characteristics of the Honghe fault before and after the 2008 Wenchuan earthquake. The results show that after the Wenchuan earthquake, the average right-lateral strike-slip rate of the Honghe fault is about 4.5 mm/a, and the strike-slip rate of the northern segment increases obviously, the strike-slip rate of the middle segment increases slightly, the strike-slip rate of the southern segment decreases obviously. The dip-slip rate on the northern segment of the Honghe fault decreases obviously, the middle and southern segments decrease slightly.After the Wenchuan earthquake, the locking and slip deficit on the northern segment of the Honghe fault increases slightly and the middle segment is the same, while the locking and slip deficit on the southern segment decreases significantly. Recently, the slip deficit on the northern segment of the Honghe fault is about 10 mm/a, the slip deficit on the middle segment is also 5～8 mm/a, and the average locking depth is about 20 km.The analysis suggests the impact of Wenchuan earthquake on the northern segment and the middle segment of the Honghe fault is relatively small, which has a great influence on its southern segment.
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jgg. 2019, 39(5): 469-475.
Using recent years flow gravity measurements from northeast China, we analyze in detail the time series variation characteristics of the flow gravity points around the Qianguo MS5.8 earthquake swarm. Based on the variation of gravity segment difference, the index values G and C are introduced to the whole and local gravity variations in northeast China, which reflects the degree of anomaly significance. Finally, we do 3D density inversion of the dynamic change of gravity field before the Qianguo MS5.8 earthquake swarm. The results show that: (1) The gravity variations on both sides of the seismogenic structure have obvious differences, which can be used as a sign to identify the tectonic activation or decoupling motion. (2) As a new method to describe the variation of regional gravity field, the significant indices G and C can provide a new idea for quantitative description of seismic gravity precursors. (3) The inversion results of gravity variation before the earthquake show that the earthquake occurred in the transitional region of mass migration, and the vertical inversion results have a certain significance for revealing the focal depth of this earthquake.
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Latest Advances of Global Ocean Tide Models and Their Accuracy Comparisons in Coastal Areas of Chinajgg. 2019, 39(5): 476-481.
A series of representative new global ocean models(TPXO, FES2014, MIKE Global Tide, Chinatide, et al.) are reviewed. Meantime, the available multi-sourced global tidal data and the latest international ocean topographic datasets are also summarized. The harmonic constituents of 26 short/middle-term tidal gauge stations along Chinese coastline are used to estimate the accuracy of 6 global ocean tide models. The comparison of RSSs formed by 8 principal constituents shows that the prediction accuracies of M2 constituents given by different GOMs are generally low in China sea, and the M2’s prediction error contributes 70%~90% of the overall accuracy. In contrast to MIKE Global Tide and TPXO7.2, the performance of TPX08, TPXO_Yellow Sea 2010 and TPXO_China&Ind are better in China coastal area.
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jgg. 2019, 39(5): 482-486.
We obtain lake elevations on the Tibetan plateau and Tianshan using CryoSat-2 baseline C level 2 products(SIR_SIN_L2I) in SARIn mode and with ICESat level 2 products, finding a bias of tens of meters between them. The bias must be removed before joint analysis of multi-mission data. Using classic waveform retracking method, the new elevation measurements are obtained from CryoSat-2 L1b products in SARIn mode. Results show that waveform retracking can remove the bias. We find that the bias is caused by a wrong window delay that is used during the production of the SARIn level 2 products. We conclude that current CryoSat-2 baseline C level 2 products in SARIn mode cannot be directly used in joint analysis of multi-mission data, and either waveform retracking or a bias correction should be added to level 2 products.
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jgg. 2019, 39(5): 487-491.
Aiming at the random and nonlinear characteristic of the time series of GPS precipitable water vapor(PWV), this paper proposes a new short-impending prediction method of GPS PWV based on wavelet decomposition(WD), genetic algorithm(GA) and least squares support vector machine(LSSVM). First, WD is used to decompose the GPS PWV time series into low frequency and high frequency components, which are easy to predict. Second, GA is used to optimize the parameters of LSSVM, and the prediction model of each component is established. Finally, the results of each component prediction are superimposed and reconstructed to get the final prediction results. In this paper, two groups of data are selected for experiments, and the prediction results are compared with those of LSSVM and genetic wavelet neural network(GA-WNN). The results show that the combined model has good generalization ability, can effectively solve the problem that neural network tends to trap in local minimum, and improves global prediction accuracy.
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jgg. 2019, 39(5): 492-495.
There are problems in calculating conventional GPS precipitable water vapor (GPS-PWV), including the large amount of data, low efficiency, and many introduced observation errors. Based on the radiosonde and GPS data collected at Chenzhou CORS station in 2015 and using linear regression and least squares methods, a new direct conversion PWV model is established from radiosonde-derived PWV (RS-PWV), GPS tropospheric delay (GPS-ZTD), ground temperature and atmospheric pressure. The direct conversion PWV model is compared with RS-PWV and GPS-PWV respectively to verify accuracy and reliability. The correlation analysis shows a favorable linear relationship between RS-PWV and GPS-ZTD, with the correlation coefficient reaching 0.927 6. The RS-PWV has positive and negative correlation with the 4-order fitting temperature and atmospheric pressure; their correlation coefficient reaches 0.640 1 and －0.626 3 respectively. The correlation coefficient between single-order single-factor model PWV based on ZTD and GPS-PWV is 0.969 9, which shows the feasibility of directly calculating PWV from ZTD. The accuracy of single-order multi-factor model based on ZTD, temperature and atmospheric pressure is significantly higher than that of single-order single-factor model based on ZTD, and RMS is increased from 4.3 mm to 3.3 mm.Therefore, the accuracy of direct conversion PWV model is slightly lower than that of GPS-PWV, but it simplifies computation and improves efficiency.
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Precision Analysis of the Tropospheric Weighted Mean Temperature Derived from GPT2w Model over Chinajgg. 2019, 39(5): 496-201.
In this study, the global geodetic observing system (GGOS) atmosphere grid atmospheric weighted mean temperature (Tm) products and radiosonde profiles in 2015 are treated as reference values to investigate the Tm derived from the GPT2w model in China. The results are: (1) the performance of GPT2w model with 1-degree resolution is better than those with 5-degree resolution, and the significant systematic errors are observed for GPT2w model in China; (2) the bias and RMS error of the Tm have obvious spatio-temporal variations, both bias and RMS present larger values in spring and winter days and smaller ones in summer days; furthermore, the RMS value of GPT2w model increases with latitude in China; (3) additionally, larger errors exist in parts of western and northeastern China, mainly due to the highly undulating terrain and the significant diurnal variations of Tm.
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jgg. 2019, 39(5): 502-505.
In order to avoid the influence of human activities, this paper uses linear least squares to extrapolate surface temperature and to discuss the statistical characteristics of extrapolation surface temperature and the measured temperature. It then applies these results to the weighted average temperature model and finds that the surface temperature based on extrapolation can significantly improve the accuracy of the model by 1.2~1.7 K.
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jgg. 2019, 39(5): 506-510.
First, based on the double-differenced positioning mathematical model and the VTEC temporal–spatial distribution of China region, we analyze the influence of higher-order ionospheric delay on L3 observation. Second, to investigate the temporal-spatial distribution characteristics of the higher-order ionospheric effect on GNSS double-differenced positioning in China region, GNSS data from 41 CMONOC stations spanning the year 2015 are processed based on the double-differenced positioning technology of BERNESE GNSS software version 5.2. Numerical results show that the influence of high-order ionospheric delay on double-differenced positioning in China region is related to the distribution of the selected stations, and there are obvious semi-annual variations and directional difference. With high latitude sites moving north and low latitude sites moving south, the size of the annual averages are up to 2 mm.
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jgg. 2019, 39(5): 511-515.
In this article we introduce the theory and usage method of the newly added zone correction parameter in BDS wide area differential service. Experimental results show that precision of code positioning without enhancement of zone correction is 2 m for horizontal, and 3 m for vertical components, whereas using zone corrections, the precision can be upgraded to 0.55 m and 0.80 m for kinematic positioning mode by using a B3 single-frequency receiver. Post processing derives higher accuracy for B1B2 dual-frequency positioning. The result shows that given continuous and stable zone corrections, the precision of B1B2 dual-frequency positioning can reach 0.35 m, 0.50 m for kinematic mode and 0.12 m, 0.22 m for static mode respectively. Zone corrections from different zones contribute to similar improvements of positioning performance. But the troposphere residuals absorbed in corrections lead to an offset of static convergent results.
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jgg. 2019, 39(5): 516-520.
In this paper, MSSA is used to simultaneously extract seasonal signals from multiple GPS stations’ elevation time series, mainly including annual and semi-annual items. The experiment verifies that MSSA can identify and extract seasonal signals in time series of GPS stations. At the same time, MSSA can use the reconstruction components(RC) to reconstruct the signals which can extract the useful signals from the original time series and remove interference noise. By comparing the percentages of the top 10 singular spectral variance and the reconstructed signals obtained from MSSA and SSA, it is shown that the MSSA reconstruction curve only contains the time-varying and common seasonal signals of multiple stations, effectively eliminating the influence of single site-specific noise and local phenomenon.
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jgg. 2019, 39(5): 521-527.
This paper analyzes the precise point positioning method of GPS, GLONASS and BDS three-system combination, including function model, estimation methods for tropospheric delay and differential code bias (DCB) parameters. The precise point positioning program based on three-system combination is developed using C++ language, and the measurements of 12 consecutive tracking stations of MEGX network are analyzed. The results show that the convergence rate and positioning accuracy of the ionospheric combination model and the non-combined model are similar and the convergence rate at the same station on different days is not significantly different. However, the non-combined model uses a priori ionospheric constraints can improve the convergence rate. Multi-system combination can reduce the PDOP value, thus improving the convergence rate and positioning accuracy. By using three-system precise point positioning, the horizontal accuracy is about 3 cm, elevation accuracy is about 5 cm. These results are better than those of three systems alone positioning or two systems combined positioning. When the cut-off elevation angle is large, the multi-system precise point positioning has higher stability than the single system.
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jgg. 2019, 39(5): 528-532.We propose an ADPPSO-BP neural network for adaptive particle swarm optimization, and an adaptive mutation operator is added into the algorithm, improving the ability of particles to jump out of local search, realizing the accurate prediction of the dam’s displacement. PSO-BP, LPSO-BP (BP neural network with line particle swarm optimization) and ADPPSO-BP algorithms are modeled to predict dam deformation. The results show that ADPPSO-BP has the highest precision and the ADPPSO-BP model is most suitable for the deformation prediction of dams.
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jgg. 2019, 39(5): 533-537.For deformation monitoring of railway slopes, three-dimensional laser scanners are used for data acquisition and voxelization. The seed growth method is used to classify the voxelized data, and its spatial parameters are fitted. By observing the distance between the point cloud data and the fitting plane of the target data classification result, the specific value of the slope deformation is obtained. Using Kalman filter to analyze multi-period data, the rate and acceleration of slope deformation is obtained, and the deformation of slope is predicted.
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jgg. 2019, 39(5): 538-543.In this paper, the traditional backward-forward selection method of gross error locating method is improved: testing the overall adjustment model, calculating the statistic correlation coefficient and using the partial correlation coefficient test are added to locate the statistics related to the gross error observation values. The simulation results show that this algorithm can accurately locate the multidimensional gross errors, effectively improve the gross errors location and transfer, and the estimation results of gross errors are reliable.
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jgg. 2019, 39(5): 544-546.First, the EIV model is linearized at the optimal solution through the GHM method and the approximate variance matrix is derived. Then, the EIV model is reformulated in the form of the Gauss-Markov model. The solution to EIV model and its approximate dispersion matrix are derived using the standard least squares theory, which is equivalent to the existing results. Finally, the statistical properties of the estimation of observations and residuals are derived and the system of parameter estimation and accuracy assessment of EIV model are established.
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jgg. 2019, 39(5): 547-550.Taking Jinghe horizontal pendulum observation data as the research object, we eliminate the influence of temperature on observation data to extract the abnormal characteristics of observed data. Then, combining this with the seismogenic structure of the earthquake, focal mechanism, station location and seismogenic tectonic relationship, etc., before the earthquake anomaly of Jinghe horizontal pendulum, we infer: (1) the NS component continues to be inclined since June 2016; (2) the EW component has been rapidly leaning since September 2016, and on 17 December the rate of leaning accelerates again by 0.48, which is caused by the stress accumulation before the magnitude 6.6 earthquake.
