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Chen P.,Xian University of Science and Technology | Chen P.,State Key Laboratory of Geodesy and Earths Dynamics | Chen J.,Wuhan University
Advances in Space Research | Year: 2014

We introduce a new global ionospheric modeling software - IonoGim, using ground-based GNSS data, the altimetry satellite and LEO (Low Earth Orbit) occultation data to establish the global ionospheric model. The software is programmed by C++ with fast computing speed and highly automatic degree, it is especially suitable for automatic ionosphere modeling. The global ionospheric model and DCBs obtained from IonoGim were compared with the CODE (Center for Orbit Determination in Europe) to verify its accuracy and reliability. The results show that IonoGim and CODE have good agreement with small difference, indicating that IonoGim owns high accuracy and reliability, and can be fully applicable for high-precision ionospheric research. In addition, through comparison between only using ground-based GNSS observations and multi-source data model, it can be demonstrated that the space-based ionospheric data effectively improve the model precision in marine areas where the ground-based GNSS tracking station lacks. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.


Xu K.-K.,Tongji University | Xu K.-K.,Henan Polytechnic University | Xu K.-K.,State Key Laboratory of Geodesy and Earths Dynamics | Wu J.-C.,Tongji University | Wu W.-W.,Tongji University
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The aseismic slip or slow earthquakes is a very important component of the seismogenic process of faults. However, it is difficult to detect these small transient signals because of the low signal-to-noise ratio (SNR) in GNSS observation data. Based on the rich GNSS spatial-temporal data in active faults, a method of integrating processing of spatial-temporal noise and detection of transient aseismic slip signals is proposed. The transient signal and spatiotemporal correlated noise are expressed by the first-order Gaussian Markov process (FOGM). The SNR in the time domain is enhanced by Kalman filtering (KF). According to the high spatial coherence of fault deformation, the SNR in the space domain is enhanced by the principal component analysis (PCA). Combining spatiotemporal filtering of PCA with KF, the SNR of GNSS observation data is further improved. The result of simulations shows that the method can properly eliminate the effect of the linear trend, the year and half year cycle, further improve the space-time SNR of GNSS spatial-temporal data, and realize the detection of the transient aseismic slip signals even though the SNR is 1:1. Taking the slow slip event in Cascadia as an example, two aseismic slip events that happened in January 2007 and April 2008 were detected clearly. The interval of the two events was about 15 months and each event shows reverse displacements. The duration was about 18 days, and the displacement was about 8 mm, mainly distributed in the south edge of Cascadia subduction zone nearly in the range of 200 km. The slip characteristics were analyzed to be consistent with the relevant literature. Using the GNSS data in western Yunnan province from 2011 to 2013 provided by Crustal Movement Observation Network of China, the weak postseismic slip signals were detected. By principal component time response analysis, from March 2011 to June 2012, the displacements of NS and EW components exhibit obvious abnormal deviations, about 6 mm and 8 mm respectively. By space response analysis, the creep deformation is mainly distributed in the south section of the Lancangjiang fault, Red River fault and Xiaojiang fault. The spatial-temporal distribution corresponds to Burma MW7.2 earthquake on March 24, 2011. It is concluded that the fault activity in western Yunnan province is closely related to the Burma earthquake. Although it is difficult to improve the SNR of the single station GNSS observation data, using the spatial-temporal series of the whole GNSS network, according to the high spatial coherence of the fault deformation, based on KF combining with PCA, allows us to reduce the space-time irrelevant noise effectively and to reveal the temporal-spatial distribution characteristics of the transient aseismic slip. It would provide an important constraint and priori information for further fine inversion of fault parameters. ©, 2015, Science Press. All right reserved.


Zhao Y.-F.,The Second Monitoring and Application Center | Zhu Y.-Q.,The Second Monitoring and Application Center | Zhu Y.-Q.,State Key Laboratory of Geodesy and Earths Dynamics | Liu F.,The Second Monitoring and Application Center
Dizhen Dizhi | Year: 2015

In this paper, according to the synthetic gravity anomaly of a horizontally infinite cylindrical geologic body, gravity gradient in horizontal direction was calculated by potential field discrete cosine transformation in frequency domain. In the calculation, the minimum curvature method was used to extend edge lines. We found that the gravity gradient field from the potential field transformation was dependable by comparison with synthetic gravity gradient, except the data in the edges. Then, the accumulative horizontal gravity gradients before Lushan MS7.0 earthquake were calculated for the accumulative gravity anomaly from September 2010 to October 2012. In the north-south direction, gravity gradient in Daofu-Kangding-Shimian and Markang-Lixian-Lushan exhibited a positive high value, and the strike of the high value zone was in line with the strike of Xianshuihe Faults and Markang Faults. In the east-west direction, high value zone was not as obvious as that in the north-south direction. Gravity gradients in the direction along and vertical to the strike of Longmenshan Faults were calculated by the definition of directional derivative. In the along-strike direction, high gravity gradient values appeared in Markang-Lixian areas along Markang Faults and Daofu-Kangding-Shimian areas along Xianshuihe Faults, and extremum appeared in Kangding-Shimian and the area nearby Lixian. In the direction vertical to the strike of Longmenshan fault zone, high gravity gradient values appeared in Lixian-Lushan-Kangding-Shimian areas, and the extremum appeared in the area nearby Kangding. The results indicate that gravity gradient in the direction along and vertical to the strike of faults can better show the relative gravity change on the two sides of faults. Lushan MS7.0 earthquake is located at the transition zone between the two high value zones of gravity gradient. The total horizontal gravity gradient shows that the location and strike of the high value zone are basically consistent with regional faults, and the extremums of total horizontal gravity gradient appeared nearby Lixian, Kangding and Shimian. © 2015, Editorial Office of Seismology and Geology. All right reserved.


Fu G.,Prediction Institute | Fu G.,State Key Laboratory of Geodesy and Earths Dynamics | Fu G.,Chinese Academy of Sciences | Gao S.,Prediction Institute | And 4 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2014

A dense relative gravity and Global Positioning System observation network with 302 stations was measured in the western Sichuan Basin (SB) to study gravity and isostasy. Bouguer Gravity Anomalies are negative in the study area, and change gradually from about -110 mGal (10- 5m s- 2) in the southeast to -220 mGal in the northwest. The new data reveal that the Moho beneath the western SB changes gradually from 39.5 km in the southeast to 43.7 km in the northwest and is inclined slightly to the northwest beneath the Chengdu Plain. The isostatic crustal thickness calculated by Airy isostatic theory varies between 39.5 and 42.0 km. The Longquan Shan (LQS) marks a clear boundary in the state of isostastic compensation in the study area. The Moho depth is almost identical to the Airy isostatic crustal thickness east of the LQS, where the crust is in isostatic balance. However, on the Chengdu Plain west of the LQS, differences between the Moho depth and Airy isostatic crustal thickness became larger from east to west, where the crust is out of isostatic balance. This indicates that the load of the Longmen Shan (LMS) on the west part of the crust of SB is mainly borne by the crust beneath the Chengdu Plain, and does little influence the crust east of the LQS. As a result we deduce that the LQS fault zone is a deeply rooted high angle fault zone that was broken by the load of the LMS. ©2014. American Geophysical Union. All Rights Reserved.


Zhang G.-Q.,Prediction Institute | Fu G.-Y.,Prediction Institute | Fu G.-Y.,University of Chinese Academy of Sciences | Fu G.-Y.,State Key Laboratory of Geodesy and Earths Dynamics | And 3 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The GRACE (Gravity Recovery and Climate Experiment) mission has continually provided the data of temporal variability of the global gravity after its launch. Several coseismic gravity changes have been successfully retrieved by the GRACE mission. The visco-elastic dislocation theory is used to study the co- and post-seismic deformations. In this paper, we study the post-seismic gravity changes due to the 2004 Sumatra earthquake (Mw9.3) based on the visco-elastic spherical dislocation theory and the GRACE data, and then analyze the viscosity of the mantle and horizontal difference at this area. We adopt the RL05 data provided by UT/CSR (Center for Space Research, University of Texas), and the data spans from January 2003 to December 2014. We replaced the Earth's oblateness values (C20) with those from Satellite Laser Ranging because of their poor accuracy. After the de-correlation filter using polynomials of degree 3 for coefficients with orders 6 or higher to alleviate longitudinal stripes and the Gaussian smoothing with averaging radius of 350 km to reduce short wavelength noises, we obtain the post-seismic gravity changes due to the 2004 Sumatra earthquake (Mw9.3) based on the difference method and time series of two points respectively located on the hanging side and the heading side. We adopt the visco-elastic spherical dislocation theory to validate the GRACE-derived result. We first use the integration of the finite fault models to solve the problem of large errors in the near-field computation using the visco-elastic spherical dislocation theory, and comparing the modified results with the results of elastic spherical dislocation theory. After that, we retrieve post-seismic gravity changes induced by the earthquake. The result shows that the peak of the gravity changes is from -8.3 to 4.6 μGal in the period of 2004-2005 based on the GRACE, which is consistent with the result derived by the elastic spherical dislocation theory in the spatial distribution and the magnitude. Based on the spatial distribution of the gravity changes and the analysis of time series, we find that the rate of the post-seismic gravity change at the heading side is 0.55 μGal/yr and the rate is 0.16 μGal/yr on the other side, which demonstrates that the viscosity of the two sides of the fault is different. The differences of coseismic vertical displacement and gravity changes based on the modified visco-elastic theory are respectively 0.06% and 0.1%, compared with those derived from the elastic spherical dislocation theory. We also analyze the Green functions of the vertical displacement and gravity changes at the source depth of 32 km in two different periods of 0~0.7 years and 0~7 years, which demonstrate that we have successfully solved the problem of large errors in the near-field computation using the visco-elastic spherical dislocation theory. Based on the corrected method, we simulate the post-seismic gravity changes due to the 2004 Sumatra earthquake (Mw9.3), finding that only when the viscosity of the heading side is 1×1018Pa·s and the viscosity of the hanging side is 8×1018Pa·s, the simulating results are consistent with the GRACE-derived results in the spatial distribution and the magnitude. Based on the theory results, we find that the rate of the post-seismic gravity changes at the heading side is 0.52 μGal/yr and the rate of the post-seismic gravity changes at the hanging side is -0.12 μGal/yr. Comparing the observing results with the simulating results, it demonstrates that the viscosity of the mantle at the Sumatra region is laterally inhomogeneous. The viscosity at the left side (the heading side) of the fault is smaller than the one at the right side (the hanging side) of the fault, and the viscosity is respectively 1×1018Pa·s and 8×1018Pa·s. ©, 2015, Science Press. All right reserved.

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