Using the rate data of vertical deformation field from 1970 to 2014 at the surroundings of Ordos block, with the help of negative dislocation inversion, we study the long-term strain accumulation. The results show that, the first average annual growth rate of energy accumulation and shear stress is the middle-northern segment of Shanxi fault belt at the northeastern margin of Ordos block, the second is the Liupanshan fracture and the western segment of Weihe fracture at the southwestern margin of Ordos block. The segments with high shear stress and relatively lower energy accumulation are the middle-southern segment of Shanxi fault belt and the border between Shanxi and Shaanxi. The western Qinling mountains tectonic area, especially the western segment of the northern margin fault of the west Qinling mountains, and the border area between Shanxi, Hebei and Inner Mongolia, also reflect the characteristics of energy accumulation.
In order to study the present-day slip rate and crustal activity characteristic of the Kunlun fault, this paper derives a regional GPS velocity field from GPS observations in the Kunlun fault region using high-precision data-processing strategy, and it then estimates present-day deformation rates of the Kunlun fault based on GPS velocity profiles. The result indicates that present-day slip rates of the Kunlun fault near 94°E, 101°E and 103°E are 12.8±1.9 mm/a, 6.1±0.9 mm/a and 0.7±2.1 mm/a, respectively. Further study and analysis show the following conclusions: (1) The present-day slip rates on the 10-year timescale along the Kunlun fault estimated by this paper are consistent with the geological results on the 104 years timescale, implying that the present-day slip rates can be a useful input data set for the seismic hazard assessment; (2) The eastern Kunlun fault has an eastward-decreasing slip rate. We argue that the crustal thickening across Anyemaqen mountains and the clockwise rotation of the eastern Kunlun fault accommodate most of the decrease; (3) The Xidatan-Dongdatan seismic gap in the Kunlun fault lies in the high-strain region.
Using the GPS velocity field of 2009-2015, the vertical velocity field of 1975-2011, and the negative dislocation model of TDEFNODE, we invert for fault locking and fault slip deficit of the north margin of west Qinling fault. Using the GPS velocity profiles and distribution characteristics of small earthquakes, this paper analyzes the fault activity and seismic risk along different segments of the north margin of west Qinling fault. The results show that the characteristic of the whole fault is left strike slip with compression, the slip rate of each segment is lower than that of the quaternary period, the slip rate of Tianshui-Baoji segment is low, the faults have the lowest activity, the earthquake distribution of the fault is few, the faults have high locking fraction and high slip deficit rate, and they have the background conditions for the occurrence of moderately strong earthquakes. Although the slip rate of the Guomatan segment is high, the fault has high locking fraction and high slip deficit rate, earthquakes are fewer, and the seismic risk is high. The slip rate of the Zhangxian and Yuanfeng segments are higher, the faults have the highest activity, the earthquake distribution of fault is greater, they have low locking fraction and low slip deficit rate, and the seismic risk is low.
Four leveling points of Xiexi site are laid along the rural highway, of which two are measured. The trend of point height difference decreases from 1997 until 2015, when the turning trend increases. According to the properties of the Xiexi fault, it is shown that the upper wall of the fault moved from sinking to floating before and after 2015, and the abnormality is verified to be environmental interference caused by the brick factory. To explain this phenomenon, the viscoelastic medium model is used and the delay time is calculated by using crossing-fault short-leveling observation data and the least square method. The results are 32 months.
In this paper, we introduce the theory of entropy using seismology. We use seismic data of 22 seismic stations in Sichuan seismic network. The permutation entropy is calculated in vertical components per hour, respectively. We study the temporal and spatial variation characteristics of the permutation entropy of ground motion before the MS8.0 Wenchuan earthquake and try to extract information about this earthquake. The results show that within 22 h before the Wenchuan earthquake, a high entropy area is formed near the epicenter. This high value area and the high value area on the north side of the Longmenshan fault system show a trend of wax and wane. The low value area on the east side of the epicenter stretches in the north-south direction, and bifurcates in the north-west direction of the epicenter. The Wenchuan earthquake occurs in the steep zone between the new high value zone and the low value zone. Combined with the findings of other scholars, we believe that these phenomena are likely to be related to the occurrence of the Wenchuan earthquake. Based on the temporal and spatial variation characteristics of the permutation entropy, we speculate that the earthquake is not only the result of the confrontation between the Bayan Har block and the Sichuan basin, but the movement of the Ordos block on the north side of the Longmenshan mountain fault system also participates in the seismogenic occurrence of the earthquake.
First, using the multiple orbital SAR data provided by Sentinel-1 satellite, we obtain the co-seismic deformation. Second, the quad-tree with data resolution constraint is used as the constraint condition for the coseismic deformation field of November 12, 2017, MW7.3 Iraq earthquake. We develop the format conversion module based on the Okada model. Inversion results show that the earthquake is located in Zagros fold and thrust belt, in which the length of the rupture zone is 44.5 km and the width is 16.1 km. The occurring mechanism of strong earthquakes is strike slip-thrust faults in which the slip angle is 140.68°, the dip angle is 8°, and the maximum slip is 3.83 m. The earthquake caused ground displacements with maximum unlift and subsidence of 50 cm and 40 cm in the satellite line of sight respectively. The depth of this earthquake is 15.5 km, with the total moment of seismic release is 0.97×1020 Nm.
In this paper, an interface is built to compute the normal modes splitting parameters, based on the MINEOS software, ode45 toolbox of MATLAB, and interpolation function. The hydrochloric coefficient of J2 and J4 are used to compute the first and second order term of Earth’s ellipticity. The splitting parameters and singlets frequencies of 0S2 are generated based on the PREM and 1066A. It is proven to be correct when compared with the results of Dahlen. Our research shows that the second order ellipticity has a little effect on the splitting parameters, but almost no influence on the singlet frequencies. Finally, the coupling matrix and coupling strength between 0S2 and selected modes are given. This lays a good base to use the splitting function to inverse the interior Earth structure.
In order to study the drought conditions in the middle and lower reaches of the Yangtze river, the southwestern region, and the north China plain, we use the GRACE time-varying earth gravity field model from 2003-01 to 2012-12 to calculate the changes in the terrestrial water reserves of the three regions. The results show the lowest value of land water storage change of the middle and lower reaches of the Yangtze river plain and the north China plain occur in May 2011, and in the southwest region the lowest value is in March 2010. According to the water balance principle of land water reserves change, we calculate the changes of groundwater reserves in the three regions. The groundwater reserves in the middle and lower reaches of the Yangtze river and the southwestern region are slowly increasing with rates of 0.54 mm/month and 0.34 mm/month. The trend reduces to a rate of 0.33 mm/month in the north China plain. The loss of groundwater reserves in the three regions during the dry period are: -21.31 mm/month in the middle and lower reaches of the Yangtze river, -19.88 mm/month in the north China plain, and -15.72 mm/month in the southwest. Finally, we use the monthly rainfall and temperature data released by NOAA to quantify the rainfall and evaporation in the three regions during the drought period. The main cause of drought in the southwestern in the spring 2010 is the temperature anomaly. The main reason for the drought of the north China plain and the middle and lower reaches of the Yangtze river in 2011 is the lack of rainfall.
We simulate and calculate the spatial distribution and the time dependent characteristics of the induced geomagnetic under different depths, intensities and changes. In addition, the distortion current intensity and distribution depth before the Minxian-Zhangxian MS6.6 earthquake in 2013 are calculated based on the electrical structural results of magnetotelluric sounding in the southeast of Gansu province. The difference between the superposition effect on the Z component and the measured data is very small. The model explains the site of a large range low point displacement before the earthquake, and the method may also be used in other areas with low point displacement with clear electrical structure.
This paper proposes a fusion method of initial position based on WiFi/PDR. In this method, the WiFi positioning results within 0.2 s after the steps are detected are set, the adjacent two-step distances and heading angles estimated in the PDR are taken as reference, the adjacent two-step WiFi positioning results are screened by the distance and angle thresholds, and the optimal positioning results are chosen according to the degree of deviation from the angle. Experimental results show that the initial position accuracy of this method is 1.2-1.8 m, which is 50% smaller than WiFi fingerprint positioning error.
In this paper, we first do 1 h, 2 h, 3 h and 4 h static PPP solutions by using short time-scale observation data from 11 GPS stations in Hong Kong, and then 4 sets of PPP coordinate sequences are obtained. Second, ocean tide loading (OTL) displacement parameters (amplitude and phase) of 8 main tidal constituents of 11 stations are obtained by harmonic analysis. Third, the misfits between PPP inversion value and ocean tide model value are analyzed. Finally, we compare the effect of correcting OTL signals by PPP inversion value and ocean tide model value. The results show that in vertical and horizontal directions, the OTL discrepancies of 8 tidal constituents inverted by static PPP with different sampling rates are about 5 mm and 7 mm, respectively; the vertical OTL of 8 tidal constituents by static PPP are better than global ocean tide model, but in horizontal direction the OTL signals inverted by static PPP are slightly weaker.
Based on more than ten years of global GPS station data, we carry out preprocessing of the detection and reparation of jumps through the wavelet transform, and introduce the PCA method to measure the station time. The feasibility and results of sequence changes are analyzed and evaluated. The most important nonlinear periodic item is extracted from the series. It shows that the principal component analysis method uses the method of orthogonal decomposition and coordinate residual space-time matrix decomposition into a number of orthogonal components. The results reveal that the residual time series shows obvious cyclical terms, and the east direction has a linear drift trend. Through the Fourier transform, the periodic term in the coordinate time series is extracted, showing that most of the global GPS stations have nonlinear periodic laws, in which annual and semi-annual cycles dominate, and the information related to geophysical phenomena is extracted for feature recognition.
In response to vacancies in the GPS coordinate time series, this paper proposes a new interpolation method based on the modeling and error spatial correlation of sites in the network, considering the intrinsic and spatial properties of the data. It proves the advantage in the interpolation for long vacancy in the example of GPS continuous GPS sites in Shaanxi province. In additional, this paper analyzes the impact of different types of vacancies on the velocity, periodic terms and noise characteristics. The results show that the vacancies have less influence on velocity but greater influence on periodic terms, and scattering vacancies affect noise characteristics greater than long vacancies. Consequently, periodic movement and noise analysis when vacancies exist have to be treated cautiously.
Classic Kalman filtering requires noise to be Gaussian white noise. However, the observation error and the state prediction error in GNSS kinematic positioning are colored noise. This paper establishes the colored noise model by using past observation residuals and state residuals in order to weaken the effects of colored noise on kinematic navigation solutions. Quad-constellations GNSS receiver measurements are used for a kinematic navigation experiment, and the results show that the algorithm can effectively improve positioning accuracy, as compared with the classic Kalman filtering algorithm with no consideration of the colored noise. The improvement rate of three-dimensional position accuracy is over 9%.
Based on data collected for 31 days at 20 stations of the Chinese coastal GNSS observation network in 2014, the method of estimating zenith tropospheric delay(ZTD) from GPS/GLONASS data in coastal areas is studied from data processing modes, system combinations and cut-off elevation angle. The ZTD products of CODE and radiosonde data are used as references to assess the estimated ZTD. The study indicates that the ZTD estimated from combined GPS/GLONASS double difference is better than that from GPS double difference and combined GPS/GLONASS precise point positioning(PPP) under 10° cut-off elevation angle. There is no obvious systematic bias in the extraction results of each method. Satellite cut-off angle setting has a great influence on the ZTD accuracy. The ZTD extracted by the double-difference network solution GPS single system has the best accuracy under 30° cut-off elevation angle, but its precision is significantly reduced compared to the results of the lower cut-off angle.
Tropospheric delay remains an important source of error. Aiming at four regions with different climatic conditions, this paper analyzes the effects of azimuth on slant tropospheric delay at various elevation angles and then proposes an approach to refine horizontal gradients of this delay. The proposed approach improves solution accuracy of VLBI data efficiently: baseline repeatability is improved by 4%, while improvement is 15% for the accuracy of estimated zenith tropospheric delay.
We establish a regional model of temperature lapse rate. After analyzing the statistic characteristics of the new model, we apply it to assess the effects of temperature lapse rate on the weighted mean temperature. The results show the high precision of temperature lapse rate is conducive to improving the distribution of the weighted mean temperature, which improves the accuracy of the PWV conversion of GPS in meteorology.
The duration of satellite low elevation angle is shorter within one day, using the same satellite’s multipath SNR to detect soil moisture results in lower temporal resolutions. In order to ensure the reliability and accuracy of soil moisture inversion results and improve their temporal resolution, in this paper, considering the approximate range of effective altitude angles, we propose a high time resolution soil moisture inversion method based on multiple GPS satellite combinations for GPS-MR. The results show that the delayed phase combination can better characterize the change trend of soil moisture. Furthermore, the correlation coefficient between delayed phase combination and soil moisture is better than 0.92. In addition, the time resolution of multi-satellite combination improves greatly, from 1 day to 2 hours.
We propose a new method to determine solution and precision evaluation of the inequality constrained partial errors-in-variables(Partial EIV) model. Under the total least square rule, the inequality constrained Partial EIV model is converted to standard optimization problems. Using the WHP(Wilson-Han-Powell) quasi Newton correction sequential quadratic programming(SQP) to solve the problem, the SUT method is used to evaluate the accuracy of parameter estimation. Simulation results show that this method can reduce iterations and increase convergence rate, the precision evaluation is simple and effective.
We introduce the measurement of Beijing Gaoyakou short gravity calibration baseline and analyze its calibration by relative gravity measurements and four times A10 absolute gravity measurements. The results show that the gravity change between basic point 5 and 2 is less than 20 μGal, and that Gaoyakou short gravity calibration baseline is steady.
The instantaneous phase of interference fringe signal sampling point is extracted based on the phase shift principle of Hilbert-transfer, the displacement data is extracted from the phase, and time data is extracted from the sample frequency. We rebuild the free-falling trajectory by means of the least square method, so that the value of g can be calculated. Zero phase-shift low-pass filter is used to remove high frequency noise signal, the polynomial fitting method is used to remove linear interference signal, and data is windowed before fitting to inhibit the Gibbs-phenomenon. The simulation results show that this method can make the g value error under 10-2 μGal. The experimental results obtained mean error of the g value is 0.12 μGal.
