15 February 2019, Volume 39 Issue 2
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jgg. 2019, 39(2): 111-116.
We study crustal dynamic deformation in the Sichuan-Yunnan region based on 1999-2015 GNSS data of CMONOC and Sichuan province CORS network. We divide into six periods of 1999-2004, 2004-2007, 2007-2009, 2009-2011,2011-2013 and 2013-2015, establish three crustal deformation models respectively, and conduct the contrast analysis. The research shows that the crustal horizontal movement is mainly inherited movement in Sichuan-Yunnan region. The crustal movement trend and the acting force are not changed by the Wenchuan earthquake, but the velocity field variations are more complex with time and increase in magnitude. Especially on the west side of the Longmenshan fault, crustal movement velocity increases obviously after the Wenchuan earthquake. The strain rate and state show obvious dynamic characteristics with time, and the high value areas are mainly located around the deep faults such as the Longmenshan, Xianshuihe and Xiaojiang faults. It shows that the fracture activity has a significant influence on crustal deformation control in the Sichuan-Yunnan region.
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jgg. 2019, 39(2): 117-121.
The vertical deformation field characteristics of the crust in Shandong area are systematically analyzed using observational data from 38 GNSS datum stations in 2011-2016. The results show that the vertical crustal deformation in Shandong area is significantly diverse. The southwestern part of Shandong area has the greatest deformation variables, where the rate of deformation is about -24.0 mm/a; the northwestern region is -15.0 mm/a. The settlement rate is small (-0.5－3.0 mm/a) in southeastern Shandong and the coastal areas. However, in the central part of Shandong area (Mount Tai Mountains) the rate of deformation is 0.3－5.0 mm/a, which shows the trend of uplift.
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jgg. 2019, 39(2): 122-126.
In this paper, we process relatively dense GPS data from continuous and campaign stations spanning over 7 years ofter the 2008 Wenchuan earthquake in the Songpan-Ganzi terrane and explore a series of viscoelastic relaxation models using the PSGRN/PSCMP program. We examined the existence of the proposed lower crust flow under the eastern Tibetan plateau. Our results show that the best-fitting steady-state viscosity of the thin low velocity zone is approximately 2.51×1018 Pa·s, while the Maxwell viscosity of the middle-lower crust beneath the Plateau is around 3.98×1018 Pa·s.
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jgg. 2019, 39(2): 127-130.
Using the three-dimensional coseismic formation GPS data of Wenchuan earthquake in 2008, combined with the dislocation model, the three dimensional velocity of Longmenshan fault is inversed by PSO. The result shows that: Longmenshan Shanqian, Longmenshan Houshan, and Longmenshan Zhongyang faults are reverse faults. Longmenshan Zhongyang fault has dextral character. The greatest velocity is at Longmenshan Zhongyang fault. The slip velocity of the fault corresponds with coseimic dislocation on earth.
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jgg. 2019, 39(2): 131-136.
According to the geophysical data obtained in the near field of the Lushan M7.0 earthquake in 2013, including the deep reflection profile and the result of P wave and S wave tomography, we establish the two-dimensional finite element model. The contact element is used to simulate the discontinuous behavior of the faults, and the numerical simulation results of the strong ground motion are further given. The results show that the ground motion parameters on hanging walls are larger than those on footwalls at the similar rupture distances, which we call the hanging-wall/foot-wall effects of near-fault ground motions. At the same time, the stress drop and cohesive force parameters have obvious positive effects on ground surface horizontal bedrock ground motion. The stress drop plays a significant role in the short period components in 0.05 s-1.00 s, and cohesion has a significant effect on the medium and long period components of 1.00 s-6.00 s.
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jgg. 2019, 39(2): 137-141.
From September to November of 2014, we laid out four deep geothermal stations near the Sichuan-Yunnan fault zones (Binchuan, Lijiang, Tengchong and Wulong). The results show that the annual cycle effect of solar radiation decreases with the increase of underground depth, and the influence of the annual activity of solar radiation basically disappears at 14m and there is a difference with theoretical calculation, which may be related to the characteristics of underground media and widely developed hot springs in Sichuan-Yunnan region. The peak of solar radiation decays exponentially with depth, and the trough increases logarithmically with depth. At the depth of 14 m, the tidal wave valley of the solar radiation basically disappears. The thermal diffusivity of different depths is retrieved by Newton iteration, and the results show that the thermal diffusivities increase with depth in Binchuan, Lijiang and Tengchong, and the thermal diffusivity of Wulong increases with depths below 4 meters. Although the range of variation is different, it basically assumes exponential function.
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jgg. 2019, 39(2): 142-147.
Using high resolution refraction and wide-angle reflection/refraction integrated seismic detection method, deep structural exploration is carried out at Huangyan, Linhai, Dongyang, Tonglu and Changhua in the central part of Zhejiang province. A velocity structure section with a length of about 350 km is obtained. The results show that the crustal structure has obvious multi layers, with three velocity discontinuities, and the velocity structure image reveals the heterogeneity of velocity structure in the basal lateral. This heterogeneity corresponds to the tectonic unit in the boundary or fracture tectonic belt, and also reflects the differences between east and west tectonic characteristics.
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jgg. 2019, 39(2): 148-152.
The geological and geophysical characteristics of the Yunxian basin segment of Yunyang-Yunxi faults are studied through geological survey and geophysical exploration. According to multiple position acquisition of Yunyang-Yunxi faults, material fracture SEM, TL test results, and combined with the data of the upper fault point sediment OSL, the Quaternary activity of the segment is analyzed. The results show that the Yunyang-Yunxi faults in the Yunxian basin section are relatively deep, the fracture characteristics are mainly reverse faults, and some branch faults show positive fault characteristics. The latest active age of the fault zone is the late Middle Pleistocene to the early Late Pleistocene.
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jgg. 2019, 39(2): 153-157.
In predicting landslide displacement using traditional ELM algorithm, the solution of ELM network output weight parameter is based on least square estimation, leading to poor resistance to gross error of ELM algorithm. To enhance the resistance to gross error of the ELM algorithm, generalized maximum likelihood estimation (M estimation) is integrated with it and M estimation-based Robust-ELM landslide deformation displacement prediction is proposed. Then, the model is applied to predicting the deformation time series data monitored at the Lianziya and Gushuwu landslides. The case studies show that the traditional ELM algorithm is sensitive to gross error in landslide data and has poor resistance to gross error. M estimation-based Robust-ELM algorithm can better resist single and multiple gross errors in landslide data and its prediction accuracy is high.
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jgg. 2019, 39(2): 158-163.
Due to potential hazards, effective monitoring of land subsidence for urban areas has for a long time been very important. In this study, based on 23 images acquired from Sentinel-1A satellite, the PS-InSAR and SBAS technology as cross validation are used to examine land subsidence of the Nanjing area. The monitoring results indicate that both the range and magnitude of the land subsidence area from PS-InSAR technology agree well with SBAS technology. Moreover, significant land subsidence of the Nanjing area has been detected between April 2015 and January 2017, with the maximum subsidence rate exceeding -30mm/a.
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jgg. 2019, 39(2): 164-168.
In order to effectively acquire the long time series deformation of mining area and monitor the influence of coal mining on railway, a railway deformation monitoring method based on TCP-InSAR (temporarily coherent point interferometric synthetic aperture radar) is studied. According to the coherence between SAR images in time series, this method selects temporary coherent points to construct Delaunay triangulation network, removes arcs with phase ambiguity between TCPs through outlier detection, and finally obtains the regional surface deformation by least squares solution. Based on 15 Sentinel-1A data from October 2016 to April 2017, using TCP-InSAR technology obtains the railway deformation in the mining area. The experimental results show that the maximum subsidence value of the railway is 95 mm and the maximum inclined slope is 0.37 per thousand during the mining period. The TCP-InSAR technology can be used to monitor the long time dynamic deformation of the railway in the mining area.
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jgg. 2019, 39(2): 169-177.
This paper studies the realization of the Beidou wide-area differential real-time ionospheric delay grid correction algorithm in China, and the short-term establishment of the ionospheric delay grid for the Beidou system. Results of BDS-only, GPS-only, and BDS/GPS combined ionospheric delay grid corrections are analyzed and compared. Results show that BDS-only and GPS-only ionospheric delay grid corrections performance are equivalent in the region, with sufficient effective grid point coverage, and the BDS/GPS combined ionospheric delay grid corrections have higher accuracy and improve the positioning accuracy of single frequency user.
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jgg. 2019, 39(2): 178-183.
Ridge estimation usually cannot be counted singly to bring the mean square error to a minimum. So, this paper proposes a ridge estimation iterative method. The ridge estimation parameter is brought into the adjustment model, the observation vector is updated, and the parameters are solved again by the ridge estimation method. The iteration is used to calculate the variance and deviation of every iteration and terminates when the mean square error reaches the minimum or the convergence. The results show that the method is effective and feasible; an example is given to demonstrate the iterative method of ridge estimation.
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jgg. 2019, 39(2): 184-188.
In the process of measuring data processing, the application of reliable prior information can effectively reduce the discomfort of the adjustment model. Based on active set thought, in this paper, using the truncated Newton method, we propose a new algorithm to solve the parameter-bounded adjustment problem. Our algorithm is more efficient than the inequality constraint, with its capacity to change the composition of the active set rapidly, and the precise evaluation of parameter value is given at the same time. Examples are given to show that the algorithm can effectively reduce the unfitness of the model and can maintain the statistical, geometric or physical significance of the parameters.
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jgg. 2019, 39(2): 189-194.
Based on the ECMWF global atmospheric model and the daily data of the surface climatological data in China, the pressure data of the meteorological stations in Xinjiang and surrounding areas are concentrated. According to the theory of elastic crustal deformation, the method of removal and recovery is adopted, and Green’s function and the spherical harmonic function method are used to study and calculate its effect on atmospheric load on the vertical and horizontal deformation of the crust, during the period from 2011 to 2015 in Xinjiang and the surrounding area. At the same time, the atmospheric admittance method is used to calculate the influence of atmospheric variance on ground gravity. The results indicate: 1) the influence of atmospheric load on vertical deformation in Xinjiang reaches the centimeter level, and the influence on ground gravity can reach 10 μGal; 2) the influence of atmospheric load has significant seasonality.
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jgg. 2019, 39(2): 195-198.
An MW9.0 earthquake occurred near the Pacific coast of Tohoku, Japan on March 11, 2011. Many internationally well-known research institutions and scholars launched different earthquake focal mechanism solutions, with many scholars evaluating these solutions. We simulate the free oscillation signal excited by the Japan earthquake. Comparing 15 seismograph observations of the seismic network in Hubei, we evaluate observations of these seismographs in low frequency band and analyze the observation ability in different frequency bands. The results show that in the 1.5 mHz to 4.5 mHz bands, there is excellent agreement between observations and synthetics; in >4.5 mHz bands, observed amplitude is significantly lower than in synthetics. In addition, we assess the observational conditions of instruments based on the spheroidal modes in the 1.5 mHz to 4.5 mHz band: most of the seismograph observation conditions are good; the conformity to simulation value and the observed value of 10 stations is up to 90%; the conformity of YC, NZH, DJI is poor.
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jgg. 2019, 39(2): 199-203.
Extreme weather events in the Amazon basin, which have occurred frequently in recent years, are generally considered to be associated with the abnormal change of rainfall, due to their strong correlation with each other. The occurrence of the El Nino/southern oscillation (ENSO) events are important factors leading to abnormal changes in rainfall. Because several extreme weather events since 2010 happened just after ENSO, it is very important to understand the impact of ENSO on the Amazon basin. Using GRACE gravity field solutions, the total water storage change (TWSC) in Amazon basin from July 2009 to April 2017 is estimated. The correlation between TWSC and ENSO index are proved to be strong with a certain time lag when trend and seasonal signals are removed. Then the different effects of ENSO on Amazon basin during dry and rainy seasons are analyzed. The results show that the dry season is significantly affected by ENSO while the rainy season is less affected. Finally, the results show that ENSO can affect TWSC in certain area by influencing the rainfall is found when combined with the hydroclimatic data analysis. This phenomenon is more prominent in the two extreme droughts in Amazon basin.
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jgg. 2019, 39(2): 204-209.
In view of the phenomenon of time-varying signal weakening and leakage in the process of GRACE data preprocessing, the scaling factors method and the forward modeling method are used to recover the lost signals. CSR Mascon products are adopted to compare the effects of the two recovery methods from the perspective of time series and spatial distribution. Results show: 1) The scaling factors method is relatively simple to implement, but the result of the scaling factors is completely dependent on the prior model, and when the reliability of the selected model is poor, the reliability of the GRACE inversion results are affected. 2) The restoration process of the forward modeling method is constrained by the original GRACE observations, and can restore the long-term trend and periodic signals, but there may be signal over-recovery in some areas. In restoring GRACE time-varying signals, we suggest using the forward modeling method.
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jgg. 2019, 39(2): 210-214.
Three absolute gravimetric points in southern Tianshan gravity network are used as adjustment data, and repeated gravity data sets of 2015-2016 are used to calibrate two CG-5 gravimeters. Then, the adjustment results before and after calibration are compared. The results show that the scale factor coefficient after calibration is significantly different than the initial value. The adjustment precision obtained by the calibration value is obviously higher than that using the initial value. Additional systematic errors are introduced by using the scale factor with error. Differentiated gravity change results show that gravity change obtained by the calibration value reduced significantly. The analysis shows that using observation data from the gravity network to calibrate the scale factor of gravimeters can reduce the influence of scale factor with error on the adjustment result effectively. It is therefore useful to eliminate the false information on gravity change.
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jgg. 2019, 39(2): 215-220.
In this paper, three main factors which directly influence the precision of determining the epicentral azimuth, namely ground-motion type, time window length and filter band, are analyzed by the polarization analysis method, based on part of KiK-net strong motion data. Results show that azimuth determined by ground displacement is outstanding compared to that determined by ground acceleration and ground velocity. Meanwhile, with calculation-time window to be valued around 1 s and filtering band to be valued between 0.1-20 Hz makes the epicentral azimuth determination results best. The results of 45-degree deviation percentage can be 88%.
