15 May 2024, Volume 44 Issue 5
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jgg. 2024, 44(5): 441-449.
Very long baseline interferometry(VLBI) plays an important role in China’s Lunar Exploration Program(CLEP). In order to obtain the accurate positioning of the lunar probe, achieve the accurate orbit determination function and complete the orbit correction during the flight of the probe, it is necessary to use the VLBI station to observe the lunar probe in real time. In this paper, we mainly use the arithmetic mean(AM) and standard deviation(STD) as precision evaluation indexes. We analyze the VLBI measured data of Chang’e-4 probe, relay satellite and Chang’e-5 probe from Shanghai Observatory for the data stability of the total observation period. Based on the simultaneous observation of the S and X bands of Chang’e-4, we emphasize the quality analysis of the data of different frequencies. We carry out time delay, time delay rate measurement error and check residual analysis for each working section of the detector, and the correlation between the motion of the detector and the data change. The results show that Chang’e-4 has the highest accuracy of 1ns among the three types of probes. Chang’e-5 probe has better observation stability than the other two types of detectors. Different ground stations have different observation accuracy of the detector, and the measured data show different characteristics in different working stages of the detector.
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jgg. 2024, 44(5): 450-455.
Global navigation satellite system(GNSS) coordinate series accuracy is mainly affected common mode error(CME) influence. In order to improve the accuracy of GNSS coordinate series, this paper adopts variational bayesian independent component analysis(vbICA) method to extract CME of coordinate series of 20 GNSS stations in the experimental site, and uses distance correlation coefficient and root mean square(RMS) as indicators to evaluate the filtering effect of the original coordinate series. The filtering performance of vbICA method is compared with PCA and ICA. The results show that the filtering effect of vbICA is obviously better than PCA and ICA. After vbICA filtering, the RMS of residual coordinate series in E,N,U direction decreases by 36.57%, 31.63% and 10.97% on average. Distance correlation coefficient decreased by 60.53%,56.84% and 25.80% on average. Considering the optimal noise model and excluding CME, GNSS velocity field estimation is more reliable and accurate, effectively improving GNSS coordinate series accuracy, and providing reliable data support for geodynamic research.
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jgg. 2024, 44(5): 456-460.
Aiming at the real-time and reliability requirements of multi-GNSS navigation satellite selection, we propose a fast satellite selection method based on improved immune algorithm. By selecting the optimal iterations number and the initial population number, the ideal satellite geometry can be obtained and the operation efficiency of receiver can be improved. The 1 day measured data of CUT0 station is used to verify the proposed algorithm. The results show when the initial population number is around 20 and the maximum iterations number is around 120, the satellite selection effect is the best. In the single BDS system, the average geometric dilution of precision(GDOP) difference is only 0.57% compared to the traversal method, and the time consuming is reduced by 53.27%. In the GPS/BDS/Galileo/GLONASS/QZSS combined system, the average GDOP difference is only 0.122 and the average time consuming is 1.06 s, which is reduced by 96.47% compared to the traversal method. The algorithm is suitable for the multi-constellation selection, and has good universality.
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jgg. 2024, 44(5): 461-467.
Using the precise ephemeris data from November 2022 for seven consecutive days as a reference, we evaluate and analyze for accuracy the real-time precise products from the 5 organizations(CAS, CNES, GFZ, SHA, and WHU). The experimental results reveal the following: CAS currently provides the highest quantity of real-time precise products for BDS-3 satellites, but the clock accuracy for MEO satellites is the lowest, exceeding 0.4 ns. GFZ’s IGSO satellite products have the poorest quality, with radial orbit errors exceeding 30 cm and clock accuracy greater than 0.8 ns. WHU’s product data quality is best, with radial orbit errors better than 4 cm and clock accuracy of about 0.16 ns, but it has only 19 available satellites. In the positioning domain, we conduct a comparative analysis of real-time precise products from various agencies using dual-frequency, ionosphere-free dynamic real-time Precise Point Positioning(PPP) techniques. The positioning results indicate that the real-time products from CNES, SHA, and WHU exhibit similar levels of positioning accuracy. The overall positioning error in both horizontal and vertical directions is approximately 0.2 meters. Taking into consideration the available number of satellites and the quality of real-time product data, we recommend that real-time PPP users utilize either CNES or SHA’s real-time products.
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jgg. 2024, 44(5): 468-472.
Aiming at the problems of low positioning accuracy and poor reliability in areas without CORS services, we propose a method for differential positioning using a self-established base station with smartphone. The method uses an external antenna to improve the quality of GNSS observation data and uses devices such as RF shielding boxes to set up a self-established base station. The Huawei Mate40 smartphone is used as a mobile station, and RTK positioning is performed with both traditional CORS base station and self-established base station. Static, walking, and cycling experiments are designed to evaluate the service capability of self-established base station. The experimental results show that in the static experiment, the RTK positioning accuracy of Huawei Mate40 smartphone with self-established base station can reach centimeter-level accuracy. In the dynamic experiment, the RTK positioning accuracy of Huawei Mate40 smartphone with both self-established base station and CORS reference station can reach decimeter-level accuracy, with a difference in planar positioning accuracy of about 0.1 m between the two methods. The self-established base station based on a smartphone can provide stable reference station services and meet the needs of surveying and mapping work in specific scenarios.
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jgg. 2024, 44(5): 473-478.
We utilize Sentinel-1 data to obtain the coseismic deformation of the 2022 Luding MW6.7 earthquake. Then. we invert the fault geometry parameters and slip model with the InSAR, GNSS, and strong motion data as constraints. The optimal fault strike, dip, and rake angles are 164.3°, 73.7°, and -3.2°. The fault ruptures to the surface, and fault motion is dominated by the left-lateral strike-slip and with a slight dip-slip. The fault slip is concentrated on the depths of 0-18 km, and the peak slip reaches 1.67 m at a depth of 7 km. We further estimate the fault kinematic parameter based on the screw dislocation model by the interseismic GNSS velocities. The fault locking depth is 17.8 km and the long-term slip rate is 10.8 mm/a. The estimated seismic moment accumulation of the Moxi segment is 9.52×1019 Nm since 1786. However, the 2022 Luding earthquake only released 12.3% of the seismic moment accumulation, indicating that the Moxi fault has a high earthquake potential. The Coulomb failure stress in the northern of the Anninghe faut is positive, which suggests the high seismic risk of the Anninghe fault.
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jgg. 2024, 44(5): 479-484.
In order to study the coseismic deformation and seismogenic fault slip characteristics of the conjugate earthquakes sequence that occurred in the east Anatolian fault system on February 6, 2023, we use D-InSAR and POT techniques to obtain the coseismic deformation field of the earthquake sequence with the Sentinel-1A data released by ESA. Based on the distributed slip model, we study the geometric form and refined slip distribution inversion of seismogenic faults after data quadtree down-sampling. The results show that the deformation trend of coseismic deformation field of the conjugate earthquakes presents an opposite change trend, and the seismogenic faults are located in the east Anatolian fault system dominated by left-lateral strike-slip. The rupture fault of MW7.8 earthquake is on the main fault zone, with a maximum slip momentum of about 10.5 m and an average slip angle of 3.74°. The rupture fault of MW7.5 earthquake is mainly on the Sügür fault, with a maximum slip momentum of about 11.8 m and an average slip angle of 1.05°. The joint analysis on focal mechanism solution given by USGS and GCMT shows that the two major earthquakes are mainly left-lateral strike-slip earthquakes with a small dip-slip component, and the occurrence of this earthquake sequence is an important manifestation of the present tectonic movement of east Anatolian fault zone.
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jgg. 2024, 44(5): 485-490.
This paper introduces the key technology, refined process, and differences in mainstream software packages for optical coseismic deformation extraction. Geoscientific operators such as displacement gradient, curl, dilatation, and shear strain are derived based on the optical coseismic deformation field. Taking the MW7.4 earthquake in Maduo, Qinghai province in 2021 as an example, we test the refined process of coseismic deformation extraction based on Sentinel-2 optical images. The results indicate post-processing of subpixel correlation matching results can effectively eliminate white noise and additive noise caused by orbit error, strip error, scenes and sensor factors, highlight deformation details, and more objectively describe the coseismic deformation spatial distribution.
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jgg. 2024, 44(5): 491-496.
Considering that BP neural network model ignores the temporal correlation of slope monitoring data, and LSTM model falls into local optimality due to the subjectivity of hyperparameter selection, we propose a slope deformation prediction model based on the combination of genetic algorithm and long short-term memory network(GA-LSTM). We utilize the global search ability of genetic algorithm and the advantages of LSTM forecasting time series data. Taking the slope of Haiming mining open-pit as the research object, we adopt BP neural network model, LSTM network model and GA-LSTM network model, respectively, to predict and analyze the GNSS49 deformation of the slope monitoring point. We compare the times for each model to reach the convergence condition. The research results show that: The time difference between GA-LSTM model and other models to reach the same convergence condition is not large. The fitting accuracy of GA-LSTM model is between 0.1 mm and 0.2 mm, which is 5 to 7 times that of LSTM neural network model and 10 to 20 times that of BP neural network model, with high accuracy and stability. The predicted value is basically consistent with the actual monitoring data, which can provide scientific basis for the safe production, management and decision control of mine slope.
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jgg. 2024, 44(5): 497-502.
We study the Jiuzhaigou MS7.0 earthquake in August 8, 2017, using observation data from 10 broadband seismometers near the epicenter before the earthquake, to calculate the permutation entropy of ground motion velocity. We investigate the relationship between the temporal-spatial variation characteristics of permutation entropy and the formation of large earthquakes. The results show that there were two abnormal episodes of permutation entropy in late July 2017; the largest one occurred at the end of July 2017. There was an entropy reduction process at all 10 stations. Among them, the decreases of permutation entropy at Maerkang(MEK), Zhouqu(ZHQ), and Diebu(DBT) stations were relatively large, with entropy values of 0.75, 0.76, and 0.79, respectively, which decrease by 12%, 12%, and 10% compared to the mean, respectively. The decrease of entropy at multiple stations indicate that there was an orderly vibration source in the crustal movement. The spatial evolution images of the low-value areas in the northeast and southwest of epicenter also indicate that there is a correlation between the abnormal change of entropy and the formation of this large earthquake. Based on previous research results, we believe that the eastward movement of Qinghai-Tibet plateau block and its blockage by the north China block and the south China block resulted in the energy accumulation of this earthquake. The Jiuzhaigou MS7.0 earthquake was triggered by upwelling and rotation of the lower crustal material after it was blocked by the Sichuan basin.
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jgg. 2024, 44(5): 503-509.
Based on the results of the first national earthquake disaster risk survey, we calculate and analyze the proportional relationship and spatial distribution characteristics of peak acceleration under different levels of exceedance probability in Hubei region. Using the macro site category data of Hubei Province, we calculate the proportion relationship of surface peak acceleration under frequent earthquakes, basic earthquakes, and fortified earthquakes. In the 0.05 g acceleration zone, the mean of the 50 years exceedance probability of 63% and 10% peak acceleration ratio(R63/R10) for sites in Hubei Province is 0.31, and the mean of the 50 years exceedance probability of 2% and 10% peak acceleration ratio(R2/R10) is 1.81; in the 0.10 g acceleration zone, the mean of R63/R10 is 0.30, and the mean of R2/R10 is 1.80; in the 0.15 g acceleration zone, the mean of R63/R10 is 0.17, and the mean of R2/R10 is 1.98. We comparatively analyze the proportion required by mandatory national standards such as current seismic design specifications for buildings and China’s seismic parameter zoning map. We infer that the seismic danger is reasonably safe in Hubei province, if rules of code for seismic design of building are followed. The peak ground motion acceleration value of frequent earthquakes should be adjusted to not less than 1/3 of the basic peak ground motion acceleration when conducting earthquake hazard analysis, earthquake disaster risk prevention and control work in high intensity areas, such as Zhushan and Zhuxi in Hubei province. The research results of this article will contribute to the promotion and application of earthquake risk survey results in Hubei province.
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jgg. 2024, 44(5): 510-516.
We utilize 195 finite fault models of strong earthquakes (MW≥7.0) released by USGS from 1990 to 2023. We employ the method of least squares fitting to derive new empirical relationships between moment magnitude(MW) and rupture length(RL), rupture width(RW), and rupture area(RA), respectively. Taking strike-slip, reverse, and normal faulting earthquakes as examples, we obtain geometric parameters of different fault types based on the new empirical relationships, which we then utilize to calculate coseismic Coulomb stress changes. The results indicate that the spatial distribution of stress enhancement and decrease obtained using the new empirical formulas closely align with the results obtained from actual rupture models, thus providing the effectiveness of the new relationships.
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jgg. 2024, 44(5): 517-521.
The time-varying gravity field obtained from the GRACE gravity satellite has significant north-south stripe errors, which greatly mask the true gravity field signal, necessitating the need for filtering processing. Based on the GRACE correlation filtering theory and the evaluation basis of the optimal signal-to-noise ratio, we analyze in detail the changes of the signal-to-noise ratio and the Gaussian weight coefficient of different Gaussian filtering half-diameter under each order. Based on this, we propose a mixed radius Gaussian filtering method, which aims to optimize the Gaussian filter weight coefficients by adjusting the filter radii at each order. The results indicate that when only the combination of 400 km classical Gaussian filtering, de-correlation filtering and 300 km classical Gaussian filtering has the best signal-to-noise ratio, two-step 400 km mixed radius Gaussian filtering, de-correlation filtering and 300 km mixed radius Gaussian filtering can further improve the signal-to-noise ratio. Additionally, these methods also effectively address the signal leakage caused by Gaussian filtering.
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jgg. 2024, 44(5): 522-527.
Aiming at the low efficiency of manual interpretation of gravity change anomaly feature region, we propose an automatic identification method using YOLOv5s algorithm to identify the four-quadrant feature area of gravity change, and conducts tests and verification based on the measured gravity change data of the north-south seismic belt. The results show that: 1) our image recognition model can effectively identify the relatively standard four-quadrant distribution feature region, and the accuracy, recall rate and average accuracy of the model prediction results are all in a reasonable range; 2) The model can accurately identify the four-quadrant feature area in the gravity change image of the north-south seismic belt from September 2021 to May 2022, and the Lushan M6.1 earthquake in June 2022 and Luding M6.8 earthquake in September 2022 in the feature area occurred successively. The results show that the proposed method has a good application potential for the screening of gravity anomaly regions and the study of potential seismic risks. 3) The recognition ability of the model for the non-standard four-quadrant feature area with obvious distortion is still insufficient, and it is still necessary to build more data training sets with more reasonable labeling to further improve the universality of the model for the recognition of the four-quadrant feature area.
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jgg. 2024, 44(5): 528-533.
This article selects the continuous observation data of three different models of gravimeters(gPhone, DZW, and GS-15) observed at the same site of Jixian seismostation throughout 2022, studies the response of different types of instruments to environmental noise, calculates the gravity noise levels of the three types of gravi meters, calculates the seismic noise levels in the seismic frequency band(200-600 s), and compares them with the seismic noise levels of gPhone gravimeters nationwide. The research results indicate that: 1) when the frequency is below 10-3 Hz, deducting solid tide and pressure correction can significantly improve the level of gravity noise; 2) The gravity noise levels of different instruments at the same station are different. The background noise level of the gPhone gravimeter is lower than that of the DZW gravimeter and GS-15 gravimeter, with an SNM value of 3.355; 3) The average noise level in the seismic frequency band of the gPhone gravimeter nationwide in 2022 is 5.418, while the average noise level at Jixian station is 3.465, which is lower than the national noise level. The research results can provide reference for the research and application of three types of gravimeter observation data.
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jgg. 2024, 44(5): 534-538.
Using numerical simulation based on the existing station layout of Shanxi Network, we quantitatively analyze the effects of crustal velocity model, network layout and seismic phase picking accuracy on seismic source location. The results show that the three factors have different effects on the accurate location of seismic source. In the crustal velocity model, the upper crust velocity has the greatest influence on the epicenter location, and the epicenter location is more sensitive to the change of Moho velocity. The deviation of epicentral position caused by a single change of crustal velocity model is usually less than 5 km, the focal depth is very sensitive to the change of crustal velocity model, especially the Moho depth, and the maximum deviation may exceed 20 km. Without considering other factors, the maximum deviation between the epicenter position and the focal depth measured within 4 s with P-wave picking accuracy is not more than 2 km and 5 km. When the crustal velocity model is suitable and the seismic phase picking accuracy is high, the station layout with the maximum void Angle of 0°-180° has a better constraint on the focal location, the epicenter deviation is basically less than 1 km, and the focal depth deviation is slightly larger, about 2 km.
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jgg. 2024, 44(5): 539-544.
We study the data of Maduo MS7.4 earthquake in Qinghai province on May 22, 2021 recorded by second sampling YRY-4 borehole strain gauge and the resampling seconds of BBVS-120 seismometer observed at Gaotai station. We carry out comparative analysis of data variation characteristics, seismological phase morphology and spectral characteristics. We find that the coseismic record of borehole strain second sampling data is clear, and the coseismic record satisfies the self-check characteristics of the four-component borehole strain observation. Both sets of instruments can record the seismic phase of the earthquake, the seismic phase morphology is similar, and the seismic phase arrival time is basically the same. The frequency spectrum and time-frequency diagram of the two sets of instruments are similar, the spectrum components are close, but the frequency distribution and amplitude change are different. This is related to the observation principle, component(direction finding) orientation, frequency bandwidth and observation sensitivity of the instrument. To further analyze the dynamic significance of borehole strain, we conduct space projection of borehole strain at different time nodes, and combined with the relative orientation of the earthquake epicenter and the station, we find that the southwest northeast 2323 and 2324 components, which are approximately close to the epicenter pointing station, and the 2321 and 2322 components distributed perpendicular to the epicenter pointing station, are in opposite tension and compression states. This may be related to the propagation laws of P and S waves.
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jgg. 2024, 44(5): 545-550.
From the aspects of consistency and correlation, we compare and analyze the observation data of the two sets of volumetric strain gauges before and after sensor replacement in Suqian earthquake monitoring center station. We find that the observation system of the newly installed volumetric strain gauge is stable, the observation data are reliable, and the observation data are highly consistent and correlated with the historical data of the original volumetric strain gauge. We consider that the two sets of data before and after the replacement can be regarded as continuous and correlated whole data for the study of crustal stress-strain field in this region.
