14 September 2018, Volume 38 Issue 9
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jgg. 2018, 38(9): 881-885.
In this paper, taking the planning area of Jiujiang Fanglan as an example, the thickness of overburden and the location and characteristics of surrounding concealed faults are obtained by means of shallow seismic reflection method. Seismic reflection profiles combined with borehole data interpretation provide abundant seismic and geological information for seismic zoning, and provide reference data for active fault detection and seismic risk assessment in this area.
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jgg. 2018, 38(9): 886-890.
Based on Okada’s elastic half-space model, the changes of Coulomb stress after the main shock are calculated and the influences of stress disturbance on the subsequent earthquakes are analyzed. The results show that: (1) Three earthquakes in the study area triggered the subsequent aftershocks which are located in areas with ΔCFS＞0. (2) The seismicity of regional background of Lintan-Tanchang is stronger than that of other areas, especially Tanchang and the adjacent areas, and the distribution of earthquakes is perpendicular to the strike of Lintan-Tanchang fault. The value of seismicity in the study area is reduced from central Tanchang to both edges gradually. (3) The seismicity in Tanchang would be higher than the seismicity of local background in the future, which needs our close attention. The seismicity of other regions in this study area are under that of the background, so the possibility of the occurrence of strong earthquakes would be smaller in the future.
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jgg. 2018, 38(9): 891-896.
Based on elastic dislocation theory, we use principal component analysis-based inversion method (PCAIM) and 531-day data from 16 GPS stations to study the temporal and spatial variation characteristics of fault slip after 2015 MW7.9 Nepal earthquake. The results show that (1) the post-seismic afterslip obeys logarithmic decay patterns; (2) the fault slip is mainly concentrated in the northern part of the mainshock rupture zone, with the maximum slip of 20.6 cm located at 26.7 km depth; (3) the inverted seismic moment is 3.36×1 020 N·m, equivalent to a moment magnitude (MW) of 7.6.
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jgg. 2018, 38(9): 897-902.
Based on a robust two-dimensional low-order polynomial fitting and weighting iterative algorithm, the gravity anomalies field of the synthetic models and those in the Sichuan-Yunnan region measured on the surface are separated vertically. The separated fields of strata with different depths from the measured gravity data are qualitatively compared with the results calculated by the interpolation-cutting potential field separation method and the geological structure map of the area as well. The results of comparison indicate the algorithms proposed in this paper are portable and reliable and can be helpful to fine inversion and interpretation of later geological structures, and other in-depth research or analysis.
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jgg. 2018, 38(9): 903-907.
We discuss the downward continuation of the horizontal component in airborne vector gravimetry using input output system, and the east component is taken as an example for a simulation test. Under different noise levels, the continued results of single-input single-output systems and double-input single-output systems are compared. The results indicate that steady downward continuation of the high precision east component can be realized using both input methods, while that of the lower precision east component can only be achieved by double-input single-output system.
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jgg. 2018, 38(9): 908-912.
Making use of the normal mode theory of the Earth, this paper studies the variations of the displacement field in the Earth’s interior and of the gravity field in the Earth’s exterior due to deformation caused by different external forces, including body and surface ones for a spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth. The operational formulas, indicating the intrinsic relation between normal modes and Love numbers, are derived to compute the Love numbers of various deformation problems of the Earth, such as tide, surface loading, as well as those due to pressure and shear forces. The numerical results demonstrate that the calculated Love numbers are in good agreement with the values derived by the numerical integration method, which validates the derived operational formulas.
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jgg. 2018, 38(9): 913-916.
This study uses earth tide data recorded with the gPhone gravimeter from January 2012 to February 2013 at Qingdao station. The tidal gravity parameters reflecting the characteristics of the station are obtained based on harmonic analysis after preprocessing of the gravity data, the gravity data are analyzed for various tidal waves (O1, K1, M2) based on eight global ocean tide loading models. The results show that (1) the amplitude factor standard deviation of eight major tidal waves are within 2.6%, and the discrepancies between the amplitude factors and the theoretical values are also within 3.0%; (2) the residual vector can be effectively reduced by using the global ocean tide model to correct the major tidal waves (O1, K1, M2), the validity of the observed residual load correction is roughly distributed over 30%-75%, and the global ocean tide model has little difference in the ocean tide load correction for the main tidal waves at Qingdao station.
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jgg. 2018, 38(9): 917-922.
This paper investigates characteristic differences between GNSS coordinate time series induced by correction of different ocean tide models. Four ocean tide models (FES2004, EOT11a, TPXO7.2 and Chinasea2010) are selected to apply ocean tide loading correction on 23 CMONOC stations in coastal areas of China. Results show that the discrepancies of diurnal tide wave parameters can lead power variations of long-period/annual/semi-annual signal up to 4.3%, 2.6% and 2.0% respectively, which is 9.1%, 0.7% and 9.6% for semi-diurnal tide wave parameters. The outcomes indicate that ocean tide loading correction by Chinasea2010 and TPXO7.2 introduces a percentage increase (up to 43%) of a particular noise model combination among stations, which is white noise plus flicker noise plus random walk noise. However, as for the uncertainty of station velocity, the correction by FES2004 remains the most significant with a reduction of uncertainty reaching 60~98% for 39% of the selected stations.
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jgg. 2018, 38(9): 923-929.
In this paper, ocean temperature and salinity data from three different Argo data processing centers (JAMSTEC, SIO, IPRC) are used to analyze global steric sea level (SSL) change at different temporal and spatial scales during 2005-2015. Our results show that the global mean steric sea level change rate (due to the seawater density variations) is 1.08±0.38 mm/a during 2005-2015. Due to strong inter-annual variations, the SSL rate during the recent period (2011-2015) is significantly greater than that over the earlier period (2005-2010) (2.16±0.50 vs. 0.66±0.64 mm/a). Up to now, the 3 Argo estimated global mean long-term SSL trends differ by ~10%, compared to their average. However, the differences reach up to 80% (of their average) for regional variations in 6 selected latitude zones (with 20° latitude widths). The spatial patterns of global seasonal and long-term SSL variations show significant differences in small regional scales (e.g., ~ 5° spatial scales) among the 3 Argo estimates, either.
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jgg. 2018, 38(9): 930-936.
According to the attenuation and leakage of signal caused by filtering in GRACE data post-processing, the corrective effect of forward modeling is studied using simulation data. It is revealed that the degree of correction is about 1 cm, which cannot be neglected when using GRACE to investigate terrestrial water storage variation. Based on GRACE RL05 Level-2 data from July 2002 to December 2014, the variation of water storage in the Three Gorges reservoir is investigated. The results reveal that the annual amplitude of GRACE time series before and after forward modeling is 7.0±2.4 cm and 7.2±2.7 cm respectively, and the leakage error reduces after correction. GRACE and hydrological models show obvious seasonal variations, but the annual amplitude of the GRACE is slightly larger than that of the hydrological model, since GRACE is influenced by many more factors. GRACE can detect the equivalent water height change of the Three Gorges reservoir, which are 60.2 mm, 28.3 mm and 20.5 mm respectively, showing good agreement with the water level observations. We analyze the equivalent water variation rates in the Three Gorges area from 2003 to 2009 before and after modeling, finding that the signal of water storage obviously converges after forward modeling correction.
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jgg. 2018, 38(9): 937-942.
In Beidou satellite real-time precise orbit determination, the filtering method has a long convergence time when using the initial orbit parameter obtained from broadcast ephemeris. To solve this problem, an enhanced method is proposed in this paper: the initial orbit parameter is derived by orbit fitting using the predicted part of ultra-rapid ephemeris and a constraint is introduced to the orbit parameter during a certain period after filtering starts. To validate our method, 7 days’ real tracking data collected from 51 globally distributed MGEX stations are used to determine BDS satellites’ real-time precise orbit based on square root information filtering(SRIF). A 3-day solution obtained in a batch estimation is used as “truth” to evaluate the precision of the real-time orbit. Results show that, an average value of 15 hours is needed before the BDS satellites’ orbit comes to a steady state with high accuracy, while a rather stable result is obtained and no obvious convergence is found during this period when the new method is used. In addition, the RMS of GEO satellites’ orbit is better than 2.5 m, 20 cm and 30 cm in along-track, cross-track and radial respectively in 7 days; meanwhile, values better than 30 cm, 15 cm and 10 cm can be achieved for IGSO and MEO satellites respectively.
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jgg. 2018, 38(9): 943-947.
This paper evaluates the accuracy of GNSS navigation positioning system. The precise ephemeris and clock bias of gbm are a true reference to contrast and analyze the orbit and clock error, which is used to count spatial signal ranging error of GPS, BDS, Galileo and GLONASS navigation files from February 1 to February 28 of 2017. The experimental results show that the accuracy of GPS orbit to the neck, tangential, normal, clock difference and SISRE is 1 m, 0.4 m, 0.8 m, 2 ns, 0.4 m respectively. Different types of BDS tracks show larger differences; the Galileo is 0.3 m, 0.3 m, 0.2 m, 3 ns and 1 m; the GLONASS is 0.4 m, 1.0 m, 0.4 m, 7 ns and 2 m.
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jgg. 2018, 38(9): 948-952.
The orbit characters of LEOs are analyzed, two sets of ephemerids model are presented, including the 22-parameter and 24-parameter ephemerids based on the 16-parameter and 18-parameter broadcast ephemerids. The analysis results of 500~1 500 km height orbit data show that the fitting URE is less than 6 cm with the 20-minute arc.
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jgg. 2018, 38(9): 953-957.
Taking as an assumption the absence of meteorological data, the author proposes a new method of zenith tropospheric delay(ZTD) prediction based on ensemble empirical mode decomposition (EEMD) and seasonal autoregressive integrated moving average models (SARIMA). The author chose ZTD data of 4 seasons in 3 different areas of China (Changchun, Shanghai and Urumqi), and did a prediction analysis. The results of the analysis show that ZTD processed prediction model with EEMD-SARIMA can satisfy calculation needs in different areas and seasons. It is a high precision ZTD forecasting method.
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jgg. 2018, 38(9): 958-963.
The dual-tree complex wavelet is introduced into the de-noising of the deformation monitoring data. The feasibility and effectiveness are comprehensively evaluated by the signal decomposition, de-noising process and de-noising quality. The theoretical analysis and examples show that the quality of signal-to-noise separation will have a great impact on threshold estimation, threshold de-noising and signal reconstruction. To a certain extent, the signal with better signal-to-noise separation can weaken the defect of threshold function. The decomposition effect of dual-tree complex wavelet is better than that of traditional discrete wavelet, and it can better display the frequency information of the detail part, so that the characteristic variation of deformation signal is more obvious. The dual-tree complex wavelet can be applied in deformation monitoring data analysis.
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jgg. 2018, 38(9): 964-967.
This paper is aimed at parameters in the actual engineering application with territorial constraints, and proposes a new adjustment algorithm with ellipsoidal constraints, whose concrete model and solving steps are given. Results of simulated experimental data and morbid trilateration net data, show that the least-squares is not suitable for processing morbid problems. Compared with the results of ridge estimation, singular value decomposition (SVD) and inequality constraints, we show that the algorithm with ellipsoidal constraints of parameter has higher precision.
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jgg. 2018, 38(9): 968-973.
A total least square with partial random parameter adjustment problem occurs if some of the estimated parameters in an adjustment problem have priori random information and the error equation coefficient matrix contains observation errors. This paper proposes a function model of total least squares adjustment with additional partial random parameters. The model has general adaptability. The algorithms formula of parameter estimation and accuracy evaluation are derived, and the steps of computation are presented, which can process the data that only partial (from 0 to all) parameter has random prior information. The feasibility, reliability and correctness of the algorithms are demonstrated by several examples and comparative analysis. The proposed algorithms have advantages in iterative convergence times.
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jgg. 2018, 38(9): 974-978.
This paper introduces the basic principles and characteristics of Morlet wavelet transform. As an example, we take the Wenchuan earthquake, using vertical continuous waveform seismometer data from May 1-12, 2008. We then acquire the time-frequency spectrums by means of Morlet wavelet transform. According to the time-frequency spectrums, the energy amplitude of the 0.1~0.2 Hz band shows an obvious increasing trend several hours before the Wenchuan earthquake. This is a frequency anomaly caused by non-typhoon disturbances, which is well in line with existing conclusions. It is proven that Morlet wavelet transform is an effective method to analyze pre-earthquake frequency characteristics.
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jgg. 2018, 38(9): 979-985.
The GPS derived global ionosphere map(GIM) by international GNSS service is used to analyze the impending ionospheric anomalies before the MW7.6 earthquake in Chile on December 25, 2016. The singular spectrum analysis (SSA) and sliding inter quartile range (IQR) method are used to detect the ionospheric anomaly preceding great earthquake, respectively. The results show the main feature of ionosphere anomalies detected by the two methods are basically the same. There are significant positive anomalies and negative anomalies on the 4th and 7th day prior to the earthquake, respectively. The ionospheric anomalies had the movement tendency from east to west in the two days, with its peak points appearing near the epicenter. The positive TEC anomalies had also been found in the conjugate area 4 days before earthquake. Compared to IQR detection, although the SSA detection highlights the main anomalous periods and spatial anomaly feature of the ionosphere, the TEC abnormal amplitude and range are smaller at the same time. Therefore, we can combine with two methods to detect the more obvious characteristics of seismic-ionospheric coupling effect. Due to the closer time to the moment of the earthquake occurrence, the results show that the ionospheric anomalies are possibly related to the earthquake, excluding other possible factors.
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jgg. 2018, 38(9): 986-990.
We use static daily superposition and the FFT spectrum analysis method to analyze month by month observation data from the Hongchiba geoelectric field, and compare the results with the Wushan establishment of geomagnetic observation data. We calculate the induced electric field in Hongchiba site during the storm, contrast this with observed data, and analyze the characteristics of the geoelectric storm. The results show that: as the month changes, the phase of static daily curve changes. The diurnal variation of the electric field at 1, 2, 11, and 12 months is significantly smaller than at the other months. The periodic component of the geoelectric field is the same as the geomagnetic field. Comparison of periodic components shows that the changes of the spectral values of the different periodic components of the geomagnetic field are in agreement with the geomagnetic D components. The geoelectric storm in a certain direction is related to the magnitude of the magnetic storm in the vertical direction; the geoelectric storm in Hongchiba site is related to the electrical structure of the area; there is a linear relationship between the observed geoelectric storm and the calculated value of geomagnetic induced current; and the relationship of geoelectric storm and magnetic index K is index.
