15 January 2023, Volume 43 Issue 1
-
Select all|
-
jgg. 2023, 43(1): 1-5.
Least-square ambiguity decorrelation adjustment(LAMBDA) algorithm involves a lot of matrix operations and takes a long time to reduce correlation in GNSS ambiguity resolution. So, we propose a blocking in least-square ambiguity decorrelation adjustment(BLAMBDA) algorithm for conditional variance matrix partitioning. In this algorithm, the conditional variance matrix is divided into blocks to reduce the ranking times of conditional variance, and on this basis, the Cholesky decomposition formula is integrated to reduce the number multiplication operation in the process of Cholesky decomposition. Simulation experiments and measured results show that, compared with LAMBDA algorithm, the overall efficiency of BLAMBDA algorithm improves significantly, and the BLAMBDA algorithm is more stable.
-
jgg. 2023, 43(1): 6-11.
We use ERA5 atmospheric reanalysis data to study the fine temporal variation of the ZTD elevation scale factor and to construct a vertical profile grid model(YZTD-H model) of the ZTD in the Yunnan-Guizhou-Sichuan region that considers the fine temporal variation of the elevation scale factor. We test the accuracy of the YZTD-H model with the layered ZTD data of radiosonde stations in the Yunnan-Guizhou-Sichuan region as reference values. We compare the results with the GPT2w and the GPT3 models. The results show that the YZTD-H model, which considers the delicate time variation and vertical profile variation shows great stability both in time dimension and vertical profile dimension.
-
jgg. 2023, 43(1): 12-17.
Based on precise point positioning(PPP),we use RTKLib, CSRS, MagicGNSS and CGline to calculate the accuracy of zenith tropospheric delay(ZTD) under different spatiotemporal conditions. The results show that: 1) The ZTD accuracy of four PPP softwares are CSRS-PPP, MagicGNSS, RTKLib and CGline from highest to lowest. 2) Under different geographical locations, the ZTD accuracy of four PPP softwares from high to low is northern hemisphere, southern hemisphere and equator. 3) The RTKlib-ZTD is greatly affected by seasons, and the RMSE are summer, spring, autumn and winter from highest to lowest, while different seasons have little influence on the ZTD of other online solution systems. In general, the average ZTD RMSE of four PPP softwares are better than 1 cm, which meets the current application of real-time and post-processing GNSS meteorology.
-
jgg. 2023, 43(1): 18-22.
Based on the BDS-2/3 satellites observable-specific signal biases(OSB) correction product published by Wuhan University observation data of eight iGMAS stations in China for one month,we analyze the influence of OSB correction on the pseudo-distance single point positioning and precision point positioning accuracy of BDS-2/3 under the combination mode of B1I/B3I old frequency points and B1C/B2a new frequency points. The results show that the mean of B1I, B3I, B1C and B2a OSB ranged from －80 ns to 70 ns, and the annual stability of OSB at each frequency point are 3.41 ns, 5.87 ns, 2.04 ns and 2.32 ns, respectively. In terms of BDS-2/3 pseudo-range single point positioning, after using OSB product correction, the positioning accuracy of B1I/B3I combination is better than 2.53 m, the positioning accuracy of B1C/B2a combination is better than 3.84 m, and the accuracy improvement is not obvious. In terms of BDS-2/3 precise point positioning, the positioning accuracy of 3D direction using B1I/B3I is better than 7.7 cm, the improvement is about 20.6%, the convergence time is about 38 min, the improvement is about 7.3%. The positioning accuracy of 3D direction of B1C/B2a is better than 3.7 cm, and the improvement is about 11.9%. The convergence time is about 36 min, improved about 16.3%.
-
jgg. 2023, 43(1): 23-28.
Based on the requirement of 99.9% envelope probability of the SF integrity parameter, this paper proposes a method to determine the service range of the satellite-based augmentation system(SBAS). Through the analysis of the integrity information broadcast by EGNOS in Europe, the service range of EGNOS calculated using this method is basically consistent with the service range announced. This method will provide support for the determination of the service range of the Beidou satellite-based augmentation system(BDSBAS) and promote the continuous improvement of the service performance of the BDSBAS.
-
jgg. 2023, 43(1): 29-33.
We analyze the application and influence of weighted total least squares method in partial errors-in-variables weight total least squares model (PWTLS), weighted total least squares method(WTLS) and least squares method(LS) in parameters calculation of the three-dimensional coordinate transformation model. Then, we deduce a coordinate transformation method that combines PWTLS and RBF Neural Network. The results show that, when both constant elements and repeated elements exist in the design matrix of coordinate transformation model, unit weighted error and precision of inner coincidence calculated by PWTLS algorithm are better than LS algorithm; in addition, correction of source coordinate calculated by PWTLS is more reasonable than WTLS. The combination method of PWTLS and RBF realizes the practicability of the parameters calculated by PWTLS, which remarkably improves the accuracy of coordinate transformation in practical application.
-
jgg. 2023, 43(1): 34-37.
Based on GPS near field displacements and teleseismic P waves, this paper applies finite fault inversion method to inverse the fault rupture process of 202-07-29 Alaska MW8.2 earthquake. The result shows that the duration of the earthquake is about 100 s and the seismic moment is about 1.59×1021 Nm. The fault rupture slip extends from the epicenter along the fault to the NEE direction, and the magnitude of fault slip is larger in the northeast side of the epicenter. The surface deformation of the earthquake is analyzed by GPS data and dislocation theory model. It is considered that the coseismic deformation is consistent with the elastic rebound model of megathrust earthquakes. Due to the fault locking, the Pacific plate subducted the north American plate, so that the upper north American plate is continuously squeezed for a long time. At the time of the earthquake, the North American plate immediately changed into tension relaxation.
-
jgg. 2023, 43(1): 38-41.
Based on the data of GNSS base station and seismic slip vector in Shandong area from 2011 to 2019, we use the block negative dislocation inversion model to inverse the fault locking degree and slip loss rate in Yishu fault zone. The results show that the fault locking degree in the south of Zhucheng of the Yishu fault zone is low, and there is no accumulation of slip deficit. The north of Zhucheng of Anqiu-Juxian fault has a higher degree of fault locking, the locking depth is relatively deep, about 26 km, and the fault sliding deficit rate is about 0.6－0.8 mm/a, which is the deficit of right-lateral extrusion. At the same time, microseismicity in this area is not active, so we need to pay attention to its seismic risk.
-
jgg. 2023, 43(1): 42-45.
For the first time, we construct a three-dimensional finite element model for the 2021 Madoi MW7.3 earthquake to analyze the features of coseismic slip distribution. First, we process the high-precision GNSS coseismic deformation observations. Then, we construct a three-dimensional finite element model, which is validated by the elastic half-space Okada model. Finally, we invert the coseismic slip distribution model of the Madoi earthquake using the least squares method, by constraining 40 near-field and far-field GNSS coseismic displacement observations. The results show that the Madoi earthquake reptures with a maximum value of about 3.4 m are mainly distributed near the area of Yematan and Huanghe country. The results are consistent with the field investigation and can well explain the GNSS coseismic deformation observations.
-
jgg. 2023, 43(1): 46-51.
Adopting the radar image of ascending and descending orbit provided by Sentinel-1A satellite, we study the coseismic deformation and focal mechanism of Menyuan earthquake. Firstly, based on D-InSAR technology, we obtain the coseismic deformation field of Menyuan earthquake. Then, taking the coseismic deformation field of ascending orbit and descending orbit as source data, we inverse fault parameters and slip distribution using the Okada uniform elastic semi-infinite dislocation model. Finally, the coseismic deformation field is forward modelled based on the coseismic sliding model. Experimental results show the maximum uplift deformations of ascending and descending coseismic deformation field along the radar line of sight are 39 cm and 58 cm, respectively. The maximum subsidence deformations of ascending and descending coseismic deformation field along the radar line of sight are all 56 cm. The earthquake is a left-handed strike-slip seismic event. The fault strikes along the NWW-SEE direction with the strike of 109° and dip of 86°. The maximum slip of 4.2 m, which is mainly concentrated in the underground 2 to 6 km. The released seismic distance of this earthquake is 8.22×1018 Nm(MW6.6). The forward results verify that the sliding distribution model is accurate and reliable.
-
jgg. 2023, 43(1): 52-60.
We construct viscoelastic deformation models and combine them with previous research results to investigate the post-seismic viscoelastic relaxation effect of six M≥7 earthquakes that occurred near the east Kunlun fault in the past century. We analyze the influence of this effect on regional crustal deformation. The results show that: 1) The crustal deformation caused by post-seismic viscoelastic relaxation of the recent 1997 Manyi M7.5 and 2001 Kunlun M8.1 earthquakes is of great significance. It can cause a crustal deformation of up to 7.6 mm/a in 10－20 a(2010－2020) after the two earthquakes, leading a cross-fault deformation rate of 8.4 mm/a. 2) The post-seismic viscoelastic relaxation of the 2021 Madoi MS7.4 earthquake is estimated to cause a maximum crustal deformation of 3.9 mm/a in the next 10 a(2021－2030), and the cross-fault deformation rate can reach 2.6 mm/a in 2025－2030. These results suggest that the effect of post-seismic viscoelastic relaxation cannot be ignored when studying the long-term crustal deformation and associated inter-seismic fault slip rate. 3) By considering the post-seismic viscoelastic deformation, the slip rate of the middle east Kunlun fault inferred from GPS velocity profile agrees well with the geological results; otherwise, the inferred slip rate will be clearly overestimated by 30%.
-
jgg. 2023, 43(1): 61-64.
We obtain the gradient for the changes of CQG2000 model, to meet the needs of height conversion between map sheets at different scales, analyze the change correlation of the variety of quasigeoid in the spatial domain. Firstly, we define the gradient model of CQG2000. Secondly, we calculate the gradient value of CQG2000 by the 3rd order finite difference weighted by reciprocal of squared distance to derive the error of the gradient and the azimuth. Finally, to analyze the change trend of national height anomaly in China, we use the gradient of CQG2000 model. The results show that the gradient value in the area east of 102° E is small, the change is soft, and the direction of azimuth is eastward; while in the area west of 102°E, the gradient value is large, the local change is abrupt, and the direction of azimuth has obvious trend changes locally. Some gradient diffusion and convergence centers exist in western regions, such as Xinjiang, Qinghai-Tibet, where there are great gradient varieties, and the maximum gradient value of 0.625 m/(′) is near Motuo.
-
jgg. 2023, 43(1): 65-70.
From May 2021 to January 2022, Madoi MS7.4, Delingha MS5.8 and Menyuan MS6.9 earthquakes occurred in Qinghai. To further explore the relationship between earthquake and magnetism, we use the three component vector data of mobile geomagnetic field from 2019 to 2021 to explore the temporal and spatial distribution characteristics of regional basic magnetic field and lithospheric magnetic field. We further explore the relationship between the annual variation of each component of lithospheric magnetic field and moderately strong earthquakes in this region. We find that the temporal and spatial distribution of the basic magnetic field in the three periods is very similar. The latest lithospheric magnetic field data before the earthquake shows that the amplitude of H vector at the epicenter of moderate and strong earthquakes changed weakly and the direction turned. The epicenter location is within 200 km from the zero line of D, I, F and Z components. The epicenter distance of Madoi MS7.4 and Menyuan MS6.9 earthquakes are only 5 km and 20 km from the zero line of Z component. In addition, it is found that some lithospheric magnetic field components show obvious anomaly one year before two strong earthquakes.
-
jgg. 2023, 43(1): 71-81.
The total horizontal derivative and the amplitude of analytic signal defined by the first derivative of gravity field data cannot balance the amplitude of shallow and deep anomalies. Inorder to solve this problem, we propose an improved boundary identification method of inclined derivative geological body using gravity full tensor gradient data called NTDM. The NTDM shows improvement in the convergence, noise suppression and boundary resolution of the new method. We obtain fourteen structural units with clear boundaries and use NTDM for the gravity data in the middle-southern segment of Tan-Lu fault zone. Then, using gravity vertical deviation data, we inverse the tectonic stress field, crust-mantle density difference. The results show that there are significant differences in horizontal direction and spatial correlation. The maximum difference of tectonic stress is about 16 MPa, and the crust-mantle density difference is about 0.2 g/cm3. The dense area of tectonic stress isolines corresponds well to the boundary of structural unit and seismic distribution. The direction of the maximum stress of the middle part of Tan-Lu fault zone is NEE-EW and the southern part is EW-NWW, and the overall direction is EW. The results are in good agreement with those obtained based on focal mechanism solution, in-situ stress measurement and GPS inversion.
-
jgg. 2023, 43(1): 82-88.
Based on focal mechanism solutions of the Yangbi earthquake sequence and historical earthquakes, we preliminarily analyze types of the focal mechanism solutions and distribution characteristics of stress axis. Further, we analyze the relationship between the focal consistency parameter and the Yangbi earthquake and historical moderate and strong earthquakes. The results show that the types of focal mechanism solutions of the Yangbi earthquake sequence and historical earthquakes are mainly strike-slip earthquakes, followed by normal earthquakes. The average Misfit angle in different radii have a certain corresponding relationship with the moderate-strong earthquakes such as Yangbi MS6.4. The focal mechanism consistency parameter all decreased before these earthquakes; that is, the focal mechanism solutions tended to be consistent. At the same time, according to the calculated b-value changes, moderate and strong earthquakes in the study area also mostly occurred in the period of b-value decline or low b-value period. When the source consistency parameter Misfit angle in the study area is lower than 40° and begins to decrease, it may indicate that the regional tectonic stress starts to concentrate. The earthquake is gradually approaching, and the risk of strong earthquakes is increasing.
-
jgg. 2023, 43(1): 89-94.
Using 190 broadband temporary stations in the Sichuan-Yunnan region from 2011 to 2013, we analyze Rayleigh surface wave phase velocity and anisotropic structure from 6 s to 60 s of the crust and upper mantle in Sichuan-Yunnan region based on eikonal equation tomography and Helmholtz equation tomography. The results show that: 1) The anisotropy direction of the upper crust is consistent with the trend of the surface structures, reflecting the tectonic movement characteristics of the southeast extrusion of the Sichuan-Yunnan block. 2) There are low velocity anomalies with strong anisotropy in the middle and lower crust of Sichuan-Yunnan block, which is consistent with the middle and lower crust flow model. 3) Bounded by 26°N, the anisotropy direction is different between crust and upper mantle in southern Sichuan-Yunnan, indicating that crust-mantle deformation is decoupled in this region. 4) The long period surface wave anisotropy direction is nearly EW direction, which is consistent with the shear wave splitting. It may be caused by the east-subduction and retracement of the Indian plate.
-
jgg. 2023, 43(1): 95-99.
Aiming at the anomaly of annual variation in time series data, we construct an information extraction process based on the S-transform method. The evolution process of the background annual variation signal(ANA) can also be analyzed in addition to the extraction of conventional short-period annual variation signal(ONA). Based on the bidirectional asymmetric threshold strategy, combined with the R value score and Molchan diagram, we construct a quantitative method for forecasting index determination and performance evaluation. The application results of the NS component of horizontal pendulum tiltmeter in the Korla station, Xinjiang, show that the ANA has better forecasting performance for M≥6 earthquakes within 250 km around the station, and the ONA is relatively better for M≥5 earthquakes within 200 km.
-
jgg. 2023, 43(1): 100-105.
In view of emanometer calibration difficulty present in earthquake stations, we advance a standard instrument calibration method for emanometer, compare it with RN-FD circulating radon gas solid source, and use RN-150 small radon gas solid source, which is the most widely used gas in current stations, to verify the feasibility of this method. The results show that the three scintillation chambers of FD-125 emanometer are calibrated by using RN-150 small radon gas solid source and AlphaGUARD P2000F emanometer; the relative deviations of the calibration coefficient are 0.2%, 3.4% and 2.8%, meeting the technical requirements of radon observation in seismic monitoring, verifing that the standard instrument calibration method is feasible.
-
jgg. 2023, 43(1): 106-110.
Based on MATLAB GUI interface, we compile a set of tide correction software GTIDE for gravity solid tide and ocean tide loading using zenith distance and Green’s function method. We analyze the reliability and applicability of GTIDE through comparison with existing international software. The results show that software is easy to operate and maintain, and its results can effectively reveal the variation characteristics of gravity solid tide and ocean tide loading. The GTIDE can be using for tide corrections of high-precision absolute gravity and relative gravity measurements.
