09 March 2017, Volume 37 Issue 3
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jgg. 2017, 37(3): 221-223.
We derive dynamic ground deformations caused by the 2015 Nepal MW7.8 and MW7.3 earthquakes on the basis of 1 Hz GPS data of crustal movement observation network of China (CMONOC) and Nepal using kinematic relative positioning method. The results show that the displacement amplitudes of eastern GPS sites of the MW7.8 earthquake are larger than the western. The kinematic deformations of each station arenot only associated with epicentral distance but also earthquake rupture propagation directivity. Dynamic ground motions caused by the MW7.3 earthquake are small. We find good agreement between high-rate GPS and strong motion displacements time series.
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jgg. 2017, 37(3): 224-229.
In order to study the three-dimensional movement of Longmenshan fault, the disclination-dislocation model of describing fault slip and rotation is proposed and used. The three-dimensional sliding and rotation of the main rupture zone is inverted with the particle swarm optimization methodand by using the measured data of GPS co-seismic data from 2008. The sliding results are contrasted with previousresearch results, and finally the reliability of the inversion results is further verified. The theoretical analysis and model calculation consequents illustrate that: firstly, the main feature of the source rupture is reverse thrusting and dextral strike-slip; secondly, the sliding and rotation of Longmenshan fault has obvious segmentation characteristics; thirdly, the seismic moment MO is 7.069×1020 Nm and the MW is 7.899 of Wenchuan earthquake. The inversed results by using the disclination-dislocation model are consistent with previous studies, therefore, the model is applicable for studying the fault activity.
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jgg. 2017, 37(3): 230-233.
The focal mechanism solutions of 68 small and medium earthquakes, whichoccurred in the southeastern margin region of Taihang mountains fault zone (TMFZ) ,are determined by the amplitude ratio of PG and SG in vertical component records with clear initial motion. The parameters of focal mechanism solutions are analyzed using statistical and cluster analysis.The average stress field azimuth of area is calculated with the method of mechanical axis tensor. The results show that the main focal mechanism solutions arestrike-slip type in the research area, and the proportion is 57%. There are also normal and inverse fault types. The dips of both maximum and minimum stress axis are small, relatively close to level. The analysis indicates that the main characteristics of the tectonic stress field of research area are nearly NEE-SWW compression and nearly NNW-SSE expansion．
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jgg. 2017, 37(3): 234-239.
This paper analyzes the seismic anisotropy parameters in the crust and obtains the characteristics of the stress field. The results show that the characteristics of the seismic anisotropy in Rushan region are influenced by both regional stress and local tectonics. Predominant polarization directions of fast shear-waves at DSDC are nearly NW. Combining the direction of epicenters of earthquake sequence and larger earthquake focal mechanism, it is concluded that the active fault in nearly NW direction is near the DSDC, and may be the possible generating fault of the RSH earthquake sequence. Polarization directions of fast shear-waves at BSTZ and CXZX are nearly EW; thus, there is probably possible active structure in nearly EW direction around the two stations.
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jgg. 2017, 37(3): 240-245.
According to the inherent defects of grey model, three kinds of grey model are improved to obtain the unbiased forecast through parameter transformation between the whitenization equation and the grey differential equation. Three case studies are used to compare the application of unbiased grey model and Origin fitting functions on deformation monitoring data processing. The results show that under the condition of a ‘small sample’,the two methods achieve about the same fitting and prediction accuracy. When modeling data is large, the unbiased grey model is not as good as the Origin fitting functions. Considering the application effect and modeling requirements, it is pointed out that the unbiased grey model has a simple modeling principle and can be used to deal with small sample deformation monitoring data. However, from a practical perspective, Origin fitting functions does not need to consider the amount of data and time interval of deformation monitoring. It is recommended to apply Origin fitting in deformation monitoring data processing.
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jgg. 2017, 37(3): 246-250.
Using 1∶500 000 Bouguer gravity anomalies data in north China, decomposed with the multi-scale wavelet transform method, we obtain the gravity anomaly from anomalous density bodies of varying scales between the earth surface and the upper Moho. By discussing details of wavelet transform of different orders and the corresponding geological tectonic features, we find the existence of an obvious corresponding relationship between the uplift and depression of north China rift-depression basin and gravity anomaly and present their extended depths. Analysis shows rocks on the two sides of the deep large fracture in the north China rift-depression basin vary widely in density and their fracture depth is inferred. With the method of Parker inversion in the Moho interface (29-42 km) in north China, it can be seen that there is an obvious crustal thickness gradient zone in the junction area between Taihang mountains and the north China plain.
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jgg. 2017, 37(3): 251-255.
Through processing and contrast analysis of 3 deep seismic sounding lines crossing Jiyang depression, we find that the crustal structure of Jiyang depression can be divided into three layers: upper, mid and lower crust. The Moho depth of Jiyang depression is about 31 km, and the interface variation is gentle. The deep tectonic is mirror symmetrical to the shallow tectonic. Low velocity bodies exist in the mid-crust of Jiyang depression, providing necessary conditions for the detachment development, and causing variations of crustallateral thickness between the upper crust and lower crust. The Moho interface feature differs between the Huimin sag and Dongying sag. In Huimin sag there is a P4 seismic phase before the Pm phase, which is the reflection of the crust-mantle transition zone. However, in Dongying sag the Pm seismic phase reflects the features of first order discontinuous interface. The result shows that the crustal structure of Jiyang depression has typical features of north China and that asthenospheric upwelling changes the Moho interface property of Jiyang depression.
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jgg. 2017, 37(3): 256-260.
This study makes use of the surface wave information in shallow reflection seismic data, inversing and extracting the shallow S-wave velocity structure. We achieve good results, which to some extent can compensate for the lack of shallow reflection data.This improves reliability of near-surface structure detection, while achieving full utilization of seismic data.
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Crustal Thickness and Poisson’s Ratio in Jiangxi and Fujian Province in Eastern Areas of South Chinajgg. 2017, 37(3): 261-266.
This paper selects tele-seismic records from 58 permanentstations setting in Jiangxi and Fujian provinces,from January 2011 and December 2012.We get information on crustal thickness and average Vp/Vs ratio estimation by the H-κ stacking method. We further obtain the image of the crustal thickness and Poisson’s ratio and their variation trend by interpolation. The study shows that: crustal thickness of the study area ranges 28-34 km,characterized by gradual thinning from inland to coast in the region of SE China margin;the southern area of Jiangxi province and the coastline of Fujian province have the thinnest crust in the study area,while the eastern area of Jiangxi province and the northwesternarea of Fujian province have thicker crust.The crustal average Poisson’s ratio ranges from 0.21-0.28,increasing from land to sea; the northern area of Jiangxi province has a low Poisson’s ratio,less than 0.23, with a Vp/Vs ratio ofless than 1.70.The coastline of Fujian province has a higher ratio,up to 0.28, with a Vp/Vs ratio of about 1.83.
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jgg. 2017, 37(3): 267-273.
We utilize the technology of high-resolution multiple coverage reflected wave method combined with first-arrival travel-time tomography inversion in one potential site for high-level radioactive waste disposal, at Alxa, Inner Mongolia. Two seismic profiles, whose total length is about 27 kilometres, are carried out across the target rock. The results of seismic detection reveal the spatial distribution, the south side unconformity boundary, and the rock’s inner structure, especially the internal faults, of the target rock. The fault structures and non-conforming strata contact relations in the interior of the mesozoic-cenozoic basin, which are located on the south of the target rock, also are clearly reflected. The seismic exploration work with large high-velocity rock as detecting target is infrequent.
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jgg. 2017, 37(3): 273-275.
The distribution of continents and oceans on the surface of the Earth possesses obvious symmetricity: if one side is covered with a continent, then the opposite side is coveredwith ocean. The symmetricaldistribution dependson the Earth structure of sphere and layer. The sketch map is worked out by elevation data of the Mars surface from ‘Google Earth’, which helps to discover the distribution symmetricity of the continents and oceans on the surface of the Mars as compared with Earth. The structure of the Earth is lithosphere, asthenosphere solid mantle sphere, and liquid core sphere, proceeding from outer to inner. Analogously, Mars possesses the same or the similar inner structure as Earth, which is the basic mode.
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jgg. 2017, 37(3): 276-281.
PWV (precipitable water vapor) is one of the meteorological factors that affects PM2.5 (particulate matter 2.5)concentration. According to the GPS and PM2.5 concentration observation data of Hebei province from January to March 2014, we analyze the correlation of GPS PWV and PM2.5 concentration based on the method of wavelet transform. First, we decompose and reconstruct GPS PWV and PM2.5 concentration series using wavelet transform method.The GPS PWV and PM2.5 concentration series reconstructed by the low frequency coefficientsreflects the positive correlation between PM2.5 and PWV. The correlation coefficients between PWV and PM2.5 concentration reconstructed by the high frequency coefficients D7 or D7 add D6 are higher than that of the original sequence. Second, we analyze the effect of PM2.5 concentration change based on the local change of PWV.The correlation coefficient between GPS PWV and PM2.5 concentration series reconstructed by the high frequency coefficients D7 add D6 amounted to 0.890. Finally, we analyze the effect of PM2.5 concentration based on different period PWV series. There is asignificantly positive correlation between PWV and PM2.5 concentration during the period of large fluctuation of PWV, while a not obvious positive correlation between PWV and PM2.5 concentration during the period of small fluctuation of PWV.
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jgg. 2017, 37(3): 282-286.In this paper, radiosonde observation data from Changsha, Huaihua, Chenzhou in Hunan province are used to establish aTmlocalizationmodelbasedonnumericalintegration and the least squares principle. The results show that the system deviation of Bevis model is 2.51 K compared with the Tm from radiosonde as a reference value. The inner precision of the Hunan Tm localization model is 1.41 K, the mean bias is 1.60 K, and the correlation coefficient is 0.942 5. Compared to the radiosonde PWV, the average bias and RMS of GPS PWV using localization Tm model are 0.52 mm and 245 mm. Experimental analyses demonstrate that the precision of the Hunan localization Tm model is better than the Bevis model. It can be applied to research on and applications of GPS meteorology in Hunan region.
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jgg. 2017, 37(3): 287-291.
Multi-GNSS can not only make full use of the advantages of different systems, but also improve the accuracy and reliability of GNSS navigation and positioning. Nevertheless, the unmodeled systematic deviation between GPS and BDS undermines inner compatibility and inter-operability. Focusing on this problem, the influence from unmodeled antenna phase center offsets of BDS on baseline solution is researched deeply in this paper, and the conclusion is validated with observation data. The results of our experiments show that systematic deviation between GPS and BDS indeed exists. After eliminating the influence of antenna phase center offsets, this systematic deviation remains.
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jgg. 2017, 37(3): 292-296.
The periodicity of BDS satellite clocks is analysed using the Fourier transformation method, and then we build the forcast model considering periodic term. On this basis, we analyze the short-term forecast effect and forecast precision of different types of satellites. Experimental results show that different types of satellites show more significant half-day and one-day period terms, and the corresponding energy amplitudes are different. Compared with the traditional quadratic polynomial forecast model, the proposed model can significantly improve prediction accuracy. The overall accuracy of 6 h prediction can be better than 2 ns and 24 h prediction accuracy better than 10 ns.
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jgg. 2017, 37(3): 297-301.
As forecast precision based on grey GM(1, 1) prediction model is low and lacks stability, weadvance a grey optimization model based on the least squares collocation.First, the optimal initial value of GM(1, 1) model is given by minimizingnew generation sequence prediction error in the least-squares sense. The exponential function method is used to construct new background values. Then, in order to improve grey optimization models, we build the prediction model of grey least squares collocation. Finally, by quantitative analysis,forecast analysis and comparison with other models, we determine that grey least squares collocation model is of high accuracy and stability. The model is more suitable for buildings and has certain engineering application value.
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jgg. 2017, 37(3): 302-305.
Based on finely processed mobile gravity observation data acquired between 2009~2012,along with seismic sounding profiles in southern north China, this paper discusses the evolutionary characteristics of surface gravity changes caused by the Taikang MS4.6 earthquake. The gravity field before the earthquake shows a four-quadrant characteristic, which is the precursor of a strike-slip earthquake on Xuchang-Taikang fault.The positive and negative gravity fields correspond exactly to the compression zone and tension zone of the focal mechanism solutions. The timing diagram of gravity difference and point value shows that the fracture strain accumulates mainly on the west and south of the Xuchang-Taikang fault, where there is a seismic low-velocity body in the crust. The strain accumulated and the different seismic velocity boundary provided conditions for the earthquake.
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jgg. 2017, 37(3): 306-310.
At present, there are two vertical reference systems that are commonly used in gravity correction. Based on this fact, we choose two profiles with large geoid variation and discuss the effect of geoid undulation on gravity reduction. The results show that the profile’s span and geoid gradient will influence on the Bouguer gravity anomaly, so when the gravity detection area’s geoid undulation has large changes, the influence of the difference between the geoid and the reference ellipsoid on the gravity reduction is more prominent. When we calculate Bouguer gravity anomaly to inversion and interpretation, the effects of geoid undulation must be considered.
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jgg. 2017, 37(3): 311-318.
We use 5 sets of GRACE data to invert the trend rates of terrestrial water storage change (TWSC) in the Tibetan plateau and adjacent areas, together with 4 types of de-striping filters and 2 types of smoothing filtersto show the variability of the results. S&W (P2M8) method with the varied-width sliding windows de-stripes more effectively, and the inverted lake water and glacier ice signals show a good consistency in the signal positions with those observed by ICESat-1 satellite altimetry. For Gaussian filter and Fan filter, the magnitudes of the main signals differ by 10-30%. Smoothing filtering usually lowers the magnitudes of the signals and reduces the spatial resolution. Even some signals of lake water and glacier ice are found to disappear. The results inverted by CSR/GFZ/JPL gravity data are close to each other and the CSR results are least impacted by the strips. The two JPL mass models MAS/MAS_S also show similar results, with the exception of a big difference in the western Plateau. Great differences are found between the results inverted from three gravity models that are calculated from two mass models. The S&W (P2M8) de-striping filter and the GRACE gravity model CSR is suggested for monitoring TWSC in the study areas.
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jgg. 2017, 37(3): 319-322.
We use the 2010-2012 gravity data from the Ningxia survey network, recalculated by a one degree term of scale parameter of the CG-5 gravimeter. We conduct a comparative analysis of the impact of correction coefficient term grid values at different time scales produced by the gravitational field before the Yinchuan ML5.0 earthquake. Our results show: (1) CG-5 gravimeter one degree scale parameter decreases with time, and continuesa declining trend; (2) different time scale gravity field changes are significantly reduced, highlighting the “0” contour phenomenon.
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jgg. 2017, 37(3): 323-326.
The reliability analysis of 4-component borehole strain data of the six sites in the Chongqing area of the Three Gorges is carried out. The strain parameters of each site is derived using relative calibration, and the local deformation characteristics in this area are obtained. The results show that the borehole strain observation data of the six sites are reliable, and the plane strain of one site is tensional, but the strain of the other five sites near the Three Gorges area is pressured. The direction of the principal strain is consistent with the direction of the regional stress, indicating the pressure characteristics of Chongqing area of the Three Gorges.
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jgg. 2017, 37(3): 327-330.
We analyze in depth the disadvantages of S transformation (ST). Firstly, the current types,principles and characteristics of GST are combined and summarized. Secondly,the present study results of GST are summarized and analyzed in seismic data processing, including time-frequency domain filtering and de-noising,time-frequency spectral decomposition,primary wave recognition,surface wave suppression,etc.Finally, we analyze and examine the potential applications of GST, which can be used to detect and extract weak seismic signals, filter the seismic data using the method of time variation,analyze the dispersion characteristics of surface wave and image with background noise,etc.
