15 June 2021, Volume 41 Issue 6
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jgg. 2021, 41(6): 551-560.
The mid-ocean ridge is the area where the ocean crust grows.It is a central rift, reflecting that the ocean is a product of tensile stress.Therefore, we must study and analyze the power source of plate movement based on the conclusion that the continental drift causes passive expansion of the ocean floor.The direction of the continental drift is regular. Inversion is performed according to the world ocean map and other data to restore the ocean and continent distribution positions at different stages.It can be seen that since the Cretaceous, the continental decomposition of the southern hemisphere has moved northward, and the continental decomposition of the northern hemisphere has moved southward.The continent moved westward as it moved towards the equator. This directional characteristic of continental drift exactly matches the directional characteristic of the Earth’s rotation force.According to the simulation experiment: the magnetic buckle with a certain quality is attracted to the middle and high latitudes of the surface of the hollow stainless-steel sphere, and the sphere is rotated. When the rotation reaches a certain speed, the magnetic buckle drifts toward the equator and westward.Similarly, because the continent on the earth is higher than the ocean, when the Earth’s rotation departure pole force of the middle and high latitudes is greater than the resistance of the ocean crust ahead, it inevitably causes the continental thrust and drift above the ocean. The theoretical calculation of Earth’s rotation departure pole force, which is generated by a continent centered at mid-latitudes, is sufficient to rupture and yield the ocean in front, so that the continental thrust drifts towards the equator. The continent moving toward the equator causes a strong westward synchronizing force due to the change in the radius of rotation, causing the ocean on the west side of the continent to rupture and the continent to drift westward. The essence of plate movement is that the continent squeezes the ocean, causing the crust of the ocean to rupture and subduct. The old ocean in front of the continent is gradually subducted and destroyed.Eventually, the continent collides with the front continent to form a new continent. Becausethe earth is a whole, the rocks behind the continent circle is under tension stress. The original continent is stretched and decomposed into two or more continents. The split continents grow along the mid-ocean ridge and grow into a new ocean. The Earth’s rotation departure pole force, formed by the rotation of the earth, in addition to causing plate motion, may also cause fractures within the lithosphere, and the accumulation and release of potential energy on existing faults may cause earthquakes.
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jgg. 2021, 41(6): 561-567.
Using the fault-crossing deformation data of 1980-2019 based on the 3D movement model of fault and the improved gray relation degree method, we study the movement characteristics and seismic hazards of the main active faults of Sichuan-Yunnan region. The results show that: 1) Xianshuihe fault zone shows a sinistral extensional movement on the whole, and has obvious segmented and differentiated movement characteristics. Zemuhe fault zone has the stage characteristics of changing from normal to reverse fault. Southern and northwestern Yunnan mainly show extensional movement. 2) The 3D accumulated activity and the synthetic index of the improved gray relation degree of the faults change obviously before and after the earthquakes of M≥6.0, which may be related to the preparation-occurrence, co-seismic and post-seismic adjustment effects of strong earthquakes near the fault. 3)Through analysis of the fault-crossing synthetic index, we conclude that we should focus on the area of the southeast segment of Xianshuihe fault zone, Zemuhe fault zone and the south of Yunnan.
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jgg. 2021, 41(6): 568-571.
To solve the problem of large monitoring error caused by insufficient spatial distribution of permanent scatterers when PSInSAR is applied to non-urban surface deformation monitoring, we propose an improved PSInSAR algorithm based on partial time scatterers(PTS). Firstly, the image is denoised by edge preserving filtering based on the improved empirical mode decomposition. Then, the PTS target is extracted by the credible probability estimation. Finally, the PTS phase is separated by parameter difference estimation and the deformation rate is calculated to obtain the surface deformation of the monitoring area. The experimental results show that the extracted PTS target basically keeps the spatial distribution characteristics and temporal variation trend of traditional PS points, which improves the spatial distribution density of non-urban target points and verifies the effectiveness of the algorithm.
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jgg. 2021, 41(6): 572-576.
We analyze the effect of altimetry satellites applied to the gravity and terrain models simultaneously on the calculation of effective elastic thickness in the South China Sea. This effect may overestimate the effective elastic thickness. Comparing multiple studies, we infer that the effective elastic thickness in the Nansha islands is 9 km. By calculating the effective elastic thickness distribution in the South China Sea, we find that the minimum effective elastic thickness of the South China Sea basin is about 4 km, and the effective elastic thickness around the South China Sea is relatively high, with strong correlation to the spatial distribution of the age of the submarine lithosphere. It also conforms to the history of the expansion of the South China Sea basin.
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jgg. 2021, 41(6): 577-583.
We use the GNSS post-seismic deformation data in the Wenchuan area from 2010 to 2015, and establish a three-dimensional post-seismic viscoelastic relaxation model using the finite element method. The two-dimensional grid search is used to obtain the optimal thickness of the elastic layer and the best viscosity coefficient of the middle and lower crust. We analyze the post-seismic deformation characteristics under the influence of viscoelastic relaxation 2-7 years after the Wenchuan earthquake. The GNSS post-seismic deformation data during 2008-2009 are used as constraints to obtain the best parameters. We compare the combined model of elastic relaxation and afterslip with the afterslip model to analyze the deformation characteristics within one year of the Wenchuan earthquake. The results show that the optimal thickness of the elastic layer in the eastern part of the Tibet plateau is 25 km, the optimal viscosity coefficient of the middle and lower crust is 4.0×1018 Pa·s. The fitting effect of the combined model is better than that of the single afterslip model within one year after the earthquake, and the afterslip deformation is the main component.
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jgg. 2021, 41(6): 584-588.
Based on data collected from local temporary and permanent seismic stations, we study the crustal velocity and focal mechanism for the 18 May, 2019 Songyuan MS5.1 earthquake in Jilin Province and the aftershocks that occurred within half a month. We use the joint inversion of receiver function and surface dispersion, the absolute travel time location and the CAP methods. The results show that the earthquake has a rupture depth of 5.8 km, a centroid depth of 8 km, and a fault plane of 303°/73°/10°. The Second Songhuajiang fault may control the occurrence of the earthquake. The Songyuan MS5.1 earthquake occurred at a depth with high velocity compared to the upper and lower layers. Our results, together with previous studies of about >5.0 earthquakes that occurred in the Songyuan area, suggest that the special velocity structure in focal area and the westward subduction of the Pacific Plate to the Songliao Basin may cause the occurrence of the Songyuan MS5.1 earthquake.
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jgg. 2021, 41(6): 589-594.
We use Sentinel-1 satellite data to obtain the coseismic deformation field of the Xaitongmoin earthquake, and invert the coseismic slip distribution model based on the homogeneous elastic half-space model. The coseismic deformation field derived from InSAR shows that the maximum deformation in the LOS direction of the ascending and descending tracks are 0.049 m and 0.051 m respectively. The long axis of the deformation field is roughly in the NW direction, which is located in the west side of Jaggang-Dinggye fault. The west dip nodal plane is more likely to be the seismogenic nodal plane through the grid search of dip and inclination. The results show that the slip distribution is mainly located within the depth range of 2-10 km, with an average slip of 0.02 m and maximum slip of 0.10 m. The dip angle of seismogenic fault is 47° and the average rake angle is -81.60°, which indicates that the earthquake is mainly normal dip slip. The epicenter of the earthquake constrained by geodetic data is 30.27°N, 87.75°E, with focal depth of 6.58 km and the moment released about 5.056×1017 Nm, corresponding to a magnitude of MW5.7, which is consistent with that from USGS and GCMT. Based on the epicenter location and the slip mechanism of this earthquake, we infer that the branch fault of Jaggang-Dinggye fault is seismogenic.
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jgg. 2021, 41(6): 595-599.
We use wavelet transform and power spectrum estimation methods, along with the brightness temperature data of the Chinese stationary meteorological satellite. Then we research the thermal infrared anomalies before the three earthquakes more than MS4.5 in Songyuan area since 2017.The results show that: Before the MS4.9 on July 23, 2017 and the MS5.7 on May 28, 2018 earthquakes, the anomalies gradually expanded along the Yilan-Yitong fault and the Mishan-Dunhua fault zone. Anomalies exist in the eastern edge of the anomaly area and the epicenter is not in the abnormal area. The anomalies are not obvious before and after the earthquake; it could be that the greenhouse gases of the basin,such as CO2 and CH4,have large releases before the two earthquakes.
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jgg. 2021, 41(6): 600-605.
The concentration of soil gases Rn, CO2, CO and H2 are measured in Huanghuayingzi and Taohuatu, which are in Chaoyang-Beipiao fault in western Liaonin province. The results of cross-fault leveling in Huanghuayingzi show that the concentrations of soil gases Rn, CO2, CO and H2 vary from 1.027 to 14.35 kBq/m3, 0.1% to 0.77%, 0.2 to 1.4 ppm and 21.45 to 303.4 ppm, respectively. The results of cross-fault leveling in Taohuatu show that the concentrations of soil gases Rn, CO2, CO and H2 vary from 1.88 to 18.15 kBq/m3, 0.23% to 4.53%, 0.2 to 2.6 ppm and 12.03 to 399 ppm, respectively. The geochemical characteristics of soil gases show that the high concentration of soil gases Rn, CO2, CO and H2 within the confines of the leveling line has a quasi-synchronous characteristic, and concentrations of some measuring points are higher than anomaly threshold. These characteristics of soil gases have revealed that the two cross-fault leveling observation sites are all passed through by the major fault of Chaoyang-Beipiao fault. The abnormal tension of the leveling data since 2018 both in Huanghuayingzi and Taohuatu are reliable, which is related to the tectonic activity.
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jgg. 2021, 41(6): 606-611.
Based on data from the Crustal Movement Observation Network of China in northeast China from 2005 to 2018, we use triangulation to construct the baseline time series of adjacent regions, and conduct temporal and spatial characteristics analysis from three aspects: spectrum characteristics, residual common mode errors, and spatial relative motion rules. The results show that the periodic effects of each component of the baseline are mainly annual and semi-annual cycles. The magnitude of the residual common mode error between baselines is about 1.14 mm horizontally and a maximum of 3.17 mm vertically. The average random effect is mainly in the east and west directions. In terms of spatial scale, the baselines that are shortened year by year are mainly in the direction of east by north, especially in the south-north component of the baseline, and the distribution characteristics of baseline length are obviously shortened in both offshore and inland regions.
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jgg. 2021, 41(6): 612-617.
There is currently little analysis of the effect characteristics of ocean tide loading worldwide in PPP, so we compare the solutions of static and kinematic PPP for 20 IGS stations before and after ocean tide model corrections of FES2004 and GOT4.7, and discuss the difference of tide waves under the two models. The test results show that the displacement in the up direction of coastal stations worldwide caused by ocean tide loading can reach 5 cm, but it does not simply increase, as sites are closer to the coastline in intercontinental and inland seas such as the Mediterranean and the Baltic Sea. Ocean tide loading effects on the coordinate error RMS in 24 h static PPP worldwide can reach several millimeters and the upgrade rate of convergence time can reach 30% after correction, but for some islands and land-sea junction zones, the correction effect of east and north directions is poor. The difference of M2 constituents in the up direction worldwide based on the two models can reach a maximum of 13 mm in offshore areas, and it is not necessarily related to ocean tide itself in terms of geographical distribution; the difference of ocean tide loading deformation has a periodic characteristic similar to ocean tide, which can reach several millimeters near the Malay Archipelago, and difference in half-diurnal tide is higher than that of diurnal tide and half-moon tide.
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jgg. 2021, 41(6): 618-622.
We research the short baseline GPS-L1/BDS-B1 tight combination non-overlapping frequencies relative positioning algorithm. We deduce, under the short baseline GPS L1/BDS-B1 non-overlapping frequencies close combination, the mathematical model of relative positioning. The GPS-L1/BDS-B1 DISB non-overlapping frequency stability and DISB calibration method is introduced in detail. The test results show that, compared with the traditional GPS/BDS loose combination relative positioning model, the compact combination relative positioning model with pre-calibrated DISB can effectively improve the success rate of fuzzy degree fixation; the fewer satellites available, the more obvious the improvement effect is.
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jgg. 2021, 41(6): 623-627.
Due to the deficiency of the traditional MAD method in detecting the gross clock error, we proposed a method of detecting and processing the gross error of clock data based on wavelet algorithm. By using the multi-scale analysis capability of wavelet transform, the data with gross errors are decomposed into the low-frequency wavelet coefficients and the high-frequency wavelet coefficients of each layer, and the gross errors are detected and eliminated at different time scales. Using the BDS clock bias data provided by CODE (Center for Orbit Determination in Europe), we analyze the performance of different wavelet functions and decomposition scale. Compared with the MAD method, we find that after preprocessing using wavelet analysis, the data has obvious advantages in clock prediction, and the average prediction precision increases by 10%.
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jgg. 2021, 41(6): 628-632.
In order to simplify the calculation of GNSS precipitable water vapor(PWV) and improve its real-time calculating efficiency, we analyze the linear relationship between GNSS-PWV and tropospheric delay(ZTD), surface temperature(T) and atmospheric pressure(P) using the GNSS data from 7stations in the Yangtze River Delta during 2017-2018. The general PWV direct transformation regional model for the Yangtze River Delta is established using the linear fitting. The experimental results show that PWV has a good correlation with ZTD, P and T, and their correlation coefficients are 0.99, -0.74 and 0.73 respectively. The RMS of the yearly single-factor PWV model based on ZTD is 3.07 mm, the RMS of the yearly double-factor PWV model based on ZTD and T is 2.35 mm, the RMS of the yearly double-factor PWV model based on ZTD and P is 1.18 mm and the RMS of the yearly multi-factor PWV model based on ZTD, T and P is 0.47 mm. The average RMS of the seasonal multi-factor PWV models based on ZTD, T and P is 0.28 mm, which is slightly better than that of the yearly multi-factor PWV model.
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jgg. 2021, 41(6): 633-638.
Aiming at the problems of low accuracy and poor adaptability in extracting building roof using LiDAR point cloud data, we propose a stepwise method for high-precision extraction of building roof point clouds. We calculate the reliability index of the point cloud through principal component analysis, select the reliable plane points, then use the K-means algorithm to realize the clustering of the reliable points in the normal vector space and extract the initial roof patch through stepwise plane estimation. Finally, we process the combination of building roof patches and the attribution judgment of unmarked points. The test results show that the proposed method has excellent extraction results, high extraction efficiency, and can obtain better extraction results for building roofs of different complexity levels.
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jgg. 2021, 41(6): 639-645.
In view of the constant deviation of the soft threshold function and the discontinuity of the hard threshold function, which results in low accuracy of signal denoising and pseudo-Gibbs phenomena, we propose an improved threshold function. We further prove its continuity, gradualness and deviation mathematically. When used with the four simulated signals with Gaussian white noise, we find that it not only improves the signal-to-noise ratio of the signal, but also compensates for the signal distortion caused by the soft and hard threshold functions. The threshold function proposed in this paper is applied to the air-gun artificial seismic source, and a conclusion consistent with the simulated signal is obtained. At the same time, compared with band-pass filtering, the method proposed in this paper can completely retain the phase and amplitude information of the signal, which proves that the improved threshold function has certain feasibility in improving the signal-to-noise ratio of the air-gun artificial source signal.
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jgg. 2021, 41(6): 646-649.
We attempt to detect the Quasi-Love wave by the normal time-frequency transform(NTFT). Surface waves come from two stations installed in Italy after the 2004-12-26 Sumatra MW9.0 earthquake. The results show that the NTFT has the ability to detect the Quasi-Love wave. The Quasi-Love wave in the NTFT is obvious, and we can also observe the characters of time-frequency change in the NTFT spectrum. Finally, we define similarity coefficient method based on the NTFT to estimate the correlation between the two signals. Compared with the cross correlation(CC) method, the similarity coefficient(SC) method performs well in the case of low SNR. We estimate the correlation between the Quasi-Love and Love wave and calculate the delay time by SC.
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jgg. 2021, 41(6): 650-654.
In this study, taking the seismic waveform data of 27 broadband seismic stations in Hubei, Hunan and Guangdong as examples, we improve the traditional background noise data processing, replacing the time domain and spectral whitening by eliminating seismic events and interference. After we remove instrument response, mean, trend, seismic events and interference, and band-pass filter (2.5-8 s) from the daily waveform data of a single station, the clear Lg-wave is identified from the cross-correlation and temporal stack data. We try to recover the relative amplitude of the Lg-wave by cross-correlation and stack time length correction, azimuth and geometrical spreading correction and site responses by reverse two-station method/two-event method. The research of this paper shows that the Lg-wave can be extracted from seismic background noise.
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jgg. 2021, 41(6): 655-660.
We calculate the abnormal changes of water temperature observation data, which contain 56 earthquakes more than MS5.0 all over the country. Then, we analyze the characteristics of intensity distribution, which can be used as one of the important references for selecting the resolution of water temperature instruments. Based on this, we carry out comparative observation experiments indifferent depths of a single well using the same type of instrument and analyzethe quantification basis of instrument resolution selectionunder different noise levels and disturbances. Meanwhile, we quantitatively analyze the selectiondetails of thesensor resolution of water temperature observation network in Yunnanand water temperature observation array in Longling. The results show that water temperature observation network in Yunnancan effectively monitor the abnormal change signals before earthquakes. However, the matching degree between the sensor resolutions and the environmental conditions of water temperature observation array in Longling should be further adjusted.
