15 September 2020, Volume 40 Issue 9
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jgg. 2020, 40(9): 881-887.
In view, not only of the challenges facing the large-scale GNSS network in data preprocessing, organization and management, selection of reference stations, processing strategies, partition schemes and quality evaluation, but also the limitation of the existing velocity field model such small data, poor continuity and timeliness, we present an integrational scheme for large-scale GNSS network data processing and establish the horizontal grid velocity field model in Chinese mainland. Based on observation data of more than 260 continuous operation reference stations in crustal movement observation network of China(CMONOC) from 2011 to 2017, we first discuss the integrated scheme of large network data processing, then give the optimization principle and quality evaluation mode for large-scale GNSS network data processing, and analyze the different evaluation strategies of the computed results, which plays an important role in high-precision data processing of a large-scale GNSS network. Finally, based on the velocity field of high-precision ITRF2014, the Kriging interpolation model is applied to construct the horizontal grid velocity field model of Chinese mainland. We utilize the accurate velocity field of all IGS stations and the regional stations to assess our results of the horizontal grid velocity field in Chinese mainland. The average and medium error of the horizontal residual velocity of the two results are less than 2 mm/a, which indicates besides good timeliness and simplicity. Therefore, the accuracy and reliability of the model can meet the requirements of users.
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jgg. 2020, 40(9): 888-891.
We analyze the differences between the Beidou ionosphere, GPS Klobuchar, and NeQuick Galileo models, and the accuracy of Beidou ionosphere models are compared with other global ionosphere models using the global ionosphere maps of IGS analysis center as the reference value. The results show that the BDGIM model possesses the best global ionosphere delay correction precision, especially in China and its surrounding areas, where the corrected percentage can reach 77.01%.
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jgg. 2020, 40(9): 892-897.
We use ionospheric model data and GIM data during solar flares in September 2017, high-energy electron storms in August 2018, geomagnetic storms in April 2017 and the Jiuzhaigou earthquake in August 2017. We analyze the influence of ionospheric anomaly on the correction accuracy of the BDS ionospheric model, and further analyze the anti-disturbance ability of ionospheric grid information. The results show that solar flares, geomagnetic storms, high energy electron storms and earthquakes, all have different effects on the ionospheric variation. During ionospheric anomaly periods, the correction accuracy of the BDS ionospheric model generally decreases, the correction rate decreases by 30% and 60%, and the anti-disturbance ability is poor, while the correction accuracy of the ionospheric grid information is basically unaffected and the anti-disturbance ability is relatively strong.
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jgg. 2020, 40(9): 898-901.
We calculate the deformation and strain characteristics of Hubei province by interpolation method based on 1998 to 2018 GPS observation data of the crustal motion observation network in China. The results reveal that the movement of the block in Hubei province is stable and without obvious deformation gradient zones. The direction of horizontal movement is east to slightly south, the speed value is between 5 mm/a and 9 mm/a with 6.2 mm/a average. The average of vertical velocity field is -0.96 mm/a, mainly sinking. The superficial expansivity shows that there are 4 high value zones of surface expansion and 4 high value zones of surface extrusion in Hubei province. The maximum shear strain rate field shows there is a high value annular zone in middle Hubei province. The distribution of historical earthquakes in Hubei province shows that earthquakes mainly occur in the edge zone of high-value stress and strain area. Small earthquakes often occur in Badong and Zigui regions, which have a certain relationship with the repeated loading and unloading of water level in the Three Gorges reservoir, and it has no obvious feature which correspond to GPS deformation and strain characteristics.
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jgg. 2020, 40(9): 902-906.
Yinchuan basin is located in the north part of the North-South seismic belt, with strong historical earthquakes and active small earthquakes. Based on InSAR technology, we use Sentinel-1 data to obtain the high spatial resolution crustal deformation rate field of Yinchuan basin and its surrounding areas between 2015 to 2019. The result shows that the whole Yinchuan basin is in a sinking trend, and there are obvious differential movements on both sides of the Helanshan eastern piedmont fault and the Yellow river fault, while the activities of Luhuatai buried fault and Yinchuan buried fault are not obvious. In this paper, the fitting formula of the surface deformation curve between earthquakes is improved, so that the inversion of fault dip, strike slip rate, dip slip rate and locking depth can be realized based on the observation value of single orbit InSAR. The algorithm is applied to the inversion of Lingwu fault activity state and locked depth, and the result shows that the strike slip rate is about 3.03 mm/a, the positive dip slip rate is about 0.27 mm/a, the locked depth is about 6.8 km, and the dip angle is about 54.7°. In addition, InSAR monitoring found large local deformation in Shizuishan and Yinchuan. After InSAR time series analysis and field investigation, we infer the deformation may be caused by human activities.
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jgg. 2020, 40(9): 907-912.
Considering the shortcomings of the traditional GM(1,1)+AR combination model, we propose a cyclic clock bias prediction model, which can update the modeling sequence in time and enhance the correlation between the data. The order of AR model is adjusted in real time according to different forecast times. Considering the influence of the original clock bias modeling sequence length on prediction accuracy, the clock bias sequences of 2 h, 6 h, 12 h and 24 h are used to build the model respectively. The results show that the prediction accuracy of the improved model is superior to the traditional method, and the prediction results are more stable. Using clock bias series with different lengths to build the model will have a certain impact on the prediction results, among which the quadratic polynomial model is relatively more affected by the length of the original series, and the improved model is relatively less affected.
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jgg. 2020, 40(9): 913-917.
In order to improve the accuracy of the prediction results caused by underground mining, we propose a surface subsidence prediction model of BP-Adaboost, which fuses chaos residuals. Taking the measured value of 1312 (1) of Gubei mine as an example, we use the BP-Adaboost models, the BP neural network model, and BP-Adaboost model fused with chaotic residuals to make one-step and multi-step predictions for the stability and active period of the maximum sinking value point, respectively. The experimental results show that BP-Adaboost model fused with chaotic residuals has the highest accuracy in both one-step prediction and multi-step prediction, especially for one-step prediction.
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jgg. 2020, 40(9): 918-922.
Based on the earthquake data recorded by Xinjiang digital seismic network, we calculate the apparent stress of the Jinghe, Xinjiang Aug 9, 2017 MS6.6 earthquake sequence. We discuss the relationship between the apparent stress of the major earthquake and the focal mechanism solution. We also discuss the relationship between the aftershock earthquake apparent stress, corner frequency and earthquake magnitude. The results show:1) There is no correlation between apparent stress and focal mechanism solution, the apparent stress of the major earthquake is higher than the aftershock earthquakes, and there is positive correlation between apparent stress and earthquake magnitude, and a negative correlation between corner frequency and earthquake magnitude; 2) 7 hours after the main shock, the apparent stress is higher in the sequence and strong aftershock, depending on the stress adjustment after strong earthquake; 3) the apparent stress before strong aftershock earthquakes is higher, returning to the low level after strong aftershock. This phenomenon also occurred in other MS6.0 earthquake sequence in middle Tianshan.
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jgg. 2020, 40(9): 923-927.
In this paper, we use the amplitude ratio method to calculate the focal mechanism solution of the 2.5≤ML≤5.0 earthquakes in the northwest margin of the Ordos block, which occurred between the year of 2000 and 2018. Through the normalized frequency statistics of the parameters of focal mechanism solution, we find that the predominant orientation of stress axis is basically consistent with the tectonic stress field in this area. Using linear stress inversion bootstrap(LSIB) method, we retrieve the direction of stress field in Bayanhot basin and Hetao seismic belt in three periods. We find that 5 years before the April 15,2015 Alxa left banner MS5.8 earthquake, the direction of stress field in Bayanhot basin deflects largely, forming an angle with the Hetao seismic belt. The direction of principal compressive stress field of Bayanhot basin obtained by inversion is consistent with the P-axis direction of this earthquake, which shows that the MS5.8 earthquake is controlled by regional stress field. After the earthquake, the direction of principal compressive stress field in Bayanhot basin is inherited, the stress field of Hetao seismic belt is affected, and the direction of the principal compressive stress field deflects and is consistent with that of the former.
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jgg. 2020, 40(9): 928-930.
In this paper, we use the Rhino software to get the topography of the Three Gorges reservoir and facilitate the topographic data to build the model in FLAC3D. The model consists of 6 layers with different parameters of the rock. After setting the mode of the calculation in FLAC3D, we get the results of the reservoir under the water level of 145 m and 175 m, based on the fluid-solid coupling theory. According to the results, the influence of pore water pressure within 3 km from surface to underground should not be ignored.
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jgg. 2020, 40(9): 931-935.
Based on the array data of Rushan, using the double-difference accurate location method, this article clarifies the sequence distribution of aftershocks occurring in Rushan, Shandong Province, since May 2014. We then invert the three-dimensional velocity model with double-difference tomography method. The data reveals that the aftershocks in Rushan generally gather circularly with a predominance distribution of 3-8 km nearby; the aftershocks of Rushan earthquake swarms occur mainly in rupture-concentrated regions, with most at the depth of 5 km, which proves that Rushan earthquake swarms happened primarily at the upper crust. The P-wave velocity at different depths in the researched regions show dramatic changes. Because of the certain distance from the already-known main faults, it can be estimated that aftershock-concentrated regions are the branch fault of Rushan or a new buried fault here.
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jgg. 2020, 40(9): 936-941.
Using seismic data of Chongqing area from January 2009 to October 2018 recorded by the Chongqing digital seismic network directory, we use the double-difference tomography method to obtain the three-dimensional velocity structure model of the upper crust in Chongqing. The results show a high correlation between the shallow crustal velocity structure and the distribution of geological structures. The fold base of the Shizhu area is missing, and the velocity structure on both sides of the fault is quite different. The difference in velocity structure between the two sides of the Huayingshan basement fault may be related to the depth and physical properties of the crystalline basement on both sides. The high-speed area of the Wuxi fault may be related to the material overflow in the deep mantle, affecting the stress distribution and seismic activity in the earth’s crust.
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jgg. 2020, 40(9): 942-946.
To study the space distribution and the shallow structure characteristic of fault zone in western piedmont of Longquanshan, we carry out a detailed field geological survey, shallow seismic section and high density resistivity detection. We discuss the fault activity based on the drilling analysis and chronological test data. The results show: there is a blind thrust fault in western Longquanshan, which is the branch of Longquanshan fault, and the tendency of the branch fault is SE. The upper fault point stops in the Holocene clay stratum, belongs to the Holocene active fault. The branch fault of Longquanshan tectonic belt is proved in the process of the thrusting from the Longquanshan to the Chengdu basin; its existence also proves that the tectonic stress is with heterogeneity, and we cannot ignore that this continuous tectonic deformation causes the earthquake risk.
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jgg. 2020, 40(9): 947-951.
Based on the three-dimensional atmospheric reanalysis model, the hydrological model and GRACE satellite gravity data from 2002 to 2017, we use Green’s function and the satellite gravity inversion method to analyze the gravity effect characteristics of large-scale surface fluid in Qinghai-Tibet plateau. The atmospheric gravity peak-to-peak effect before and after deducting seasonal term is between 1.9-10.7 μGal and 1.1-4.6 μGal, respectively, which shows significant seasonal characteristics. The gravity peak-to-peak effects of soil water and snow before and after deducting seasonal term is between 0.9-9.9 μGal and 0.7-8.3 μGal, respectively, which shows significant seasonal and interannual characteristics. The peak to peak change of GRACE time variable gravity field is between 4.4-24.1 μGal and 3.4-18.3 μGal before and after deducting seasonal term. Considering measurement error, tectonic movement and leakage error, the significant seasonal and interannual change of GRACE gravity reflects the combined effects of various surface fluids.
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jgg. 2020, 40(9): 952-956.
We are concerned with the applicability and selection of different remove-restore elevation conversion models in the process of quasi geoid refinement. We construct RBF neural networks, polyhedral function and Shepard function based on quadratic surfaces, and an EGM2008 gravity field model. We apply these tools to two engineering examples in the plain and plateau mountains, in order to fit normal height and compare the accuracy of each model by adjusting the number of fitting points. Experiments show that in the plain area, the accuracy of the EGM2008-polyhedral functions elevation model is slightly better than the other five models; in the plateau mountainous area, when the number of fitting points is fewer, the accuracy of the remove-restore models based on EGM2008 is higher than the corresponding models based on quadratic surfaces, and the EGM2008- polyhedral function model and the EGM2008-Shepard model are superior. As the number of fitting points increases, the accuracy of the quadratic surfaces-Shepard transformation model is better than the other five models.
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jgg. 2020, 40(9): 957-961.
In this paper, we calculate the ionospheric TEC disturbance caused by the 2015 MW7.8 Nepal earthquake and analyze the FFT spectrum based on GPS observation data to research temporal and spatial characteristics of earthquake ionospheric TEC. The results show that obvious abnormal disturbance appears 5 minutes after earthquake and lasts more than 6 minutes with a trend of increasing-decreasing-increasing. The disturbance propagates towards east, northeast and several directions, whose velocities are 2 336.36 m/s and 455.52-937.64 m/s. The center frequencies are mostly 3-7 mHz, which is consistent with the disturbance spectrum caused by Rayleigh wave and acoustic wave.
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jgg. 2020, 40(9): 962-969.
We select three components of continuous waveform data observed by six seismic stations from August 14 to December 31, 2017 in MS7.0 Jiuzhaigou earthquake emergency mobile network, and then calculate the noise PSDs and corresponding PDFs. Compared with the new earth noise models(NHNM and NLNM), we analyze the variation characteristics of the noise level of emergency mobile stations. The results show that there are no obvious geometrical variations of noise in the high-frequency band of seismic station, the noise sources affecting the horizontal and vertical components noise levels of the stations are different, or the same noise source has different intensity in the horizontal and vertical components. Affected by culture noise and natural noise, the average noise level is significantly higher than the average of NHNM and NLNM, and some stations are close to or above the NHNM. Both culture and natural noise are broadband. Culture noise is closely related to the actions of human beings at or near the surface of the earth, shows very strong diurnal variations, and can generate a single frequency of fixed noise in a fixed period of time. The running water in small streams can produce continuous high-frequency natural noise. The noise level differs in different frequency bands, and the diurnal variation is not obvious.
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jgg. 2020, 40(9): 970-975.
In-situ calibration is vital for quantitative borehole strain observation. In order to prompt the application of borehole strain observation to the investigation of geodynamics, we review the recent investigation of in-situ calibration methods for borehole strain observation from calibration model and strain reference. We indicate the key issues and future directions.
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jgg. 2020, 40(9): 976-980.
In this paper, we establish the motion model of the two-stage vibration isolation system, then derive and analyze the closed-loop transfer function of the system. The analysis results show that when PID feedback is adopted, the equivalent damping coefficient of the system can be adjusted more conveniently than the PD feedback used in the current ultra-long spring(superspring). The equivalent natural period of the system is mainly affected by the feedback proportional coefficient kp; the larger the kp is, the longer the equivalent natural period, and the system will have better vibration isolation performance. After kp is selected, the integral coefficient ki together with the differential coefficient kd will affect the damping of the system, and ki is dominant, which determines the stability of the system. The accuracy of the closed-loop transfer function analysis results are verified by simulation, which show that the vibration isolation effect of the system can reach -70 dB at 1 Hz.
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jgg. 2020, 40(9): 981-984.
The fiber of absolute gravimeter laser is easily deflected around the optical axis, due to stress, shape change, vibration or coupler maintenance, etc. The polarization state of the output laser is destroyed, making its transmission in the optical fiber very unstable, resulting in an optical fiber output laser extinction ratio of less than 100, which cannot meet the absolute gravimeter observation conditions. This paper introduces a method of adjusting the optical fiber alignment, and the extinction ratio detection device is designed to check whether the extinction ratio is greater than 100. Alignment adjustment experiments are carried out on the optical fibers of the two WEO100 He-Ne lasers #181 and #250, and we meet the absolute gravimeter measurement conditions by measuring the beam extinction ratio of the output of the two lasers by the extinction ratio detection device. The research shows that the alignment adjustment method is scientific and effective.
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jgg. 2020, 40(9): 985-990.Space distance standard device is an important metrological standard for the calibrating terrestrial laser scanner. The measurement of the space distance of the target ball has always been a difficult problem. At present, most are measured by laser tracker. In this paper, we propose the coordinate measurement of target sphere by total station intersection survey. Firstly, the outline coordinates of feature points can be obtained quickly and conveniently by rear rendezvous and non-prism measurement. Then, the orientation datum can be established by mutual aiming. Finally, the high-precision coordinates of feature points can be obtained by overall adjustment. The example proves that the accuracy of this system is better than 0.1 mm, and it can meet the calibration accuracy requirement of space distance standard device.
