This paper presents temporal and spatial variations of the gravity field in Nepal and its periphery. It further explores the regional long-term gravity changes prior to the April 25 2015, M8.1 Nepal earthquake by using GRACE satellite gravity data. Co-seismic geoid and gravity changes based on spherical dislocation theory are simulated with the fault model. The results show obvious characteristics of regional gravity field features in different periods, i.e., gravity increases during 2003-2008 and decreases during 2009-2014. Meanwhile the regional gravity field around the epicenter is in the center of positive and negative changes. Compared with theoretical gravity variation, the GRACE regional gravity field shows similar results, gravity increases in the compression zone and reduces in the tension area. This research reveals that earthquakes occur in the transition zone of gravity gradient changes and around zero line of gravity variations. GRACE gravity variations before an earthquake provide an important basis to explore the earthquake focal mechanism and earthquake predictions.
The Mw7.8 Nepal earthquake occurred on April 25, 2015, with several strong aftershocks that caused effects in the Tibetan areas of China. In order to predict the strong aftershocks of Nepal earthquake, an improved “waiting time” model using weighted least square fitting is proposed based on the theoretic residual analysis. The new model is then applied to the Nepal earthquake sequences to better predict outcomes. Results indicate that the proposed method effectively reduces model prediction errors as well as the confidence interval. Also the prediction errors are zoomed by ln10·Δt (Δt is the waiting time of the last aftershock) from model axis to real time axis. For this reason, the aftershock samples should be chosen within 3 days of the main earthquake.
Numerous buildings and facilities in Shigatse, southwest of Tibet, were hit by the Nepal M8.1 earthquake on April 25, 2015, with an epicenter intensity of IX degree. The civil structures and stone-wood structure houses are damaged more seriously than masonry structures and frame structure buildings. The damage along the Brahmaputra river is greater than in other districts, because of the deep Quaternary overburden. Seismic geological disasters, such as landslide and rockfall, caused heavier casualties and property losses than the ground motion itself.
Deccan faults striking NNE with a total length of about 120 km, consisting of Luozuo fault, Madian fault, Luhe fault, etc, are located near the dam site of Wudongde hydropower. The fault weakens to the north and forms into multiple branch faults in a nearly parallel 6km wide broom-like arrangement to the south. The fault rocks are cataclasite as a result of brittle deformation. All kinds of secondary structures in the fault zone show that the fault has undergone many tectonic activities in the new tectonic period, and the activity intensity is weakening. The latest fault activity was in Middle Pleistocene, mainly by stick slip motion. The largest earthquake magnitude of the faults are M6.0 in the Luozuo fault and M5-5.5 in the Madian and Luhe faults, by the evaluation of seismic risk.
Coulomb stress changes along the Xianshuihe fault induced by the Wenchuan, Lushan and Kangding earthquakes are calculated and compared with long term tectonic loading rates in order to assess seismic potential change on the fault due to these earthquakes. The results show that the Kangding earthquake was advanced and delayed by the Wenchuan and Lushan earthquakes, respectively.Most of the Coulomb stress changes along the Xianshuihe fault are due to the Wenchuan and Kangding earthquakes.Under a linear stress loading assumption, advance/delay times of earthquake recurrence are calculated along the fault.In the case assuming μ′=0, the earthquake recurring times could be advanced by approximately 0-5 years at locations between Bamei and Moxi〖JP2〗（except the rupture zone of the Kangding earthquake), and delayed by 0-4 years at the other regions, respectively.If μ′=0.4, the advance times of earthquake recurrence are estimated as 0-6 years in the range between Daofu and Zhuyaozihaizi, and the delay times are calculated to be 0-2 〖JP3〗years out of the range.As our knowledge is so limited about the rheological structures on both sides of the Xianshuihe fault, the impact of its variation on the results is also investigated.Our research shows that the lower the viscosities of the lower crust and the upper mantle, the larger the Coulomb stress change due to viscous relaxation would be, and the more rapidly it changes along fault strike.Furthermore, the contribution of the viscous relaxation is comparable to that of coseismic rupture, resulting in advance/delay times of earthquake recurrence of up to 3 years.
Based on previous analyses, interpretation of remote sensing images and geological survey, the seismic geological environment in the Bortala region is studied and assessed. Using the deterministic seismic hazard analysis method, the trend of seismic activity is discussed. The result shows that the seismic geological characteristics of the Bortala region are similar to the South Tianshan and east part of north Tianshan regions. Both of these regions are related to the north Tianshan seismic zone, in which there exists a risk of strong earthquake.
In this paper, current vertical mobility of Shanxi is studied, according to observational data, calculation of vertical deformation variables and the vertical deformation rate of leveling across the Shanxi rift zone section. Since 2006, the vertical deformation of Shanxi with the northeast of the Yanhuai and Weixian basins show rising tilting activity. Further, north of the Yangyuan and the Datong basins present decreasing activity, the Jinzhong basin fluctuates and the Linfen basin shows rising activity. However, the tipping point of Shanxi activity appears in 2013. The Weixian basin has decreased by a large margin. The Datong, Daixian-Dingxiang, Jinzhong and Linfen basins have risen to varying degrees.
For the characteristics of complex geological structure in mountainous areas, this research studied the existing 3D geologic model building method. Based on existing geological survey data, it innovatively realizes the process from building the section frame, drawing the profile, to building the geological model. Using this approach, we can build the regional geology 3D model of a mountainous areas more accurately. In the research, the resultant models can be integrated into the 3D digital city platform. In the 3D scene of the platform, we can query the regional geological situation. The result of this research explores new ideas in the fusion of the development of geological information and the digital city.
Using the model CRUST 1.0, we analyze the structure of upper crust thickness and the moho discontinuity in Sichuan-Yunnan region. Then we calculate the regional isostatic moho discontinuity based on the Airy isostatic theory. With the difference between the isostatic and the real moho discontinuity, we study the state of crustal equalization in the Sichuan-Yunnan region. Comparing the map of upper crust thickness with the depth distribution diagram of regional earthquakes, we found that regional earthquakes mainly occurred in the upper brittleness crust. The crustal isostatic apparently shows that the Sichuan basin is in an isostatic state. However, the Longmen mountain’s fault zone poses a state which is out of the isostatic, and represents the most remarkable disequilibrium area in Sichuan-Yunnan region, whose north side presents positive equilibrium (+6 km), south side presents negative equilibrium (-6 km) and southwest side presents positive equilibrium (+6 km). All of this possibly reflects that the deep crust material beneath Longmen Mountain’s fault zone is undergoing a dramatic differentiation, adjustment and intense exchange of energy.
We get the coordinate time series by solving CMONOC GNSS reference stations during 2011-2013 and calculate the non-tectonic deformation on sites produced by non-tidal ocean, atmospheric conditions, snow, and soil moisture. The GNSS vertical series has significant changes corrected by non-tectonic deformation: the amplitude and initial phase of annual motion present significant changes, and the amplitude reduced (individual sites increasing) and the narrow margin varies in different regions. The initial phase has a systematic bias before and after correction, with about 2-3 months lag, such that the systematic biases may be the effect of the GNSS sites’ overall “slow response” to geophysical factors. The change of semi-annual motion reflects principally on the amplitude, with a narrow margin of about 1 mm.[
〗In this paper, we explore the crustal deformation in the Capital circle region (114°-119°E, 39°-41°N) before and after the March 11, 2011 M9.0 Tohoku earthquake, according to the cross-fault leveling data in this area. Then we construct the three-dimensional finite element model in the Capital circle region, and preliminarily analyze the dynamic mechanics that reflect the deformation behavior, through the cross-fault observation line in different geometric structures. The results show that (1) the cross-fault leveling data expresses the unanimous characters that reflect the same fault activity type, in which the leveling variation changes from 0.07 mm in Babaoshan and Shangwan sites to 1.09 mm in Jingxi proving ground with the vertical intersecting line| (2) the hanging wall drops vertically relative to the opposite for the NNE-NE and the NW strike faults, which represents the tensional activity| (3) the vertical results of the cross-fault baseline with different directions, which are deduced from the numerical model, also illustrate the same fault activity style as the observed results (i.e., the hanging wall drops vertically relative to the heading wall)| and (4) the nearly EW trending tensile stress is mainly responsible for the unanimous deformation behavior in the Capital circle region.
How to choose the relative weight ratio λ is an important problem that deserves to be studied in inversion models when using more than two physical measurements, including the geodetic displacements to implement the joint inversion. The idea of computing the λ with it and other inversion parameters as the parameters to be inverted is put forward, and the inversion model is derived in detail. Through simulated data and the solution, the effectiveness and feasibility of the method above is proven.
Firstly, in the least square collocation, we get the preferable regional velocity field based on WGS-84 ellipsoid from the polynomial function, the Gaussian function, the homo-Gaussian function, the Hirvonen function, the space harmonic functions (two), and six different kinds of covariance function. Then, through the better method, we get the GPS strain field of the study area by using rotation in the entire block and homogeneous strain model (REHSM). Eventually, we analyzed the 19 GPS sites based on the “digital seismic network project’s” 2007-2010 GPS monitoring data in the Yuncheng basin.
A new algorithm based on gray least squares support vector machine for dam deformation prediction is presented. First, the algorithm of the original dam sequence is summed to weaken the impact of the random disturbance factors sequence and enhance the data regularity. Second, the least squares support vector machine model is established. The grid search method is used to select the optimal parameters. This method makes full use of least squares support vector machine generalization ability| the nonlinear fitting of good quality characteristics avoids defects of the theoretical methods and gray models. The calculation result is analyzed and compared with GM (1, 1) and a single least squares support vector machine. The results show that the new algorithm can guarantee the optimum value of the local forecasts and better overall prediction accuracy in dam deformation. It is feasible to apply the model in short-term forecasts.
Based on major national construction projects in recent years in gravity network and the earthquake in Yunnan province regional gravity network we obtained high accuracy gravity observation data, the analysis and research on October 7, 2014, Yunnan Jinggu M6.6 earthquake before the evolution process of gravitational field. The results showed that The evolution on Yunnan southwest regional gravity field changes the amplitude of the big, fast speed, rising and falling transition cycle is short, revealing the complex tectonic environment and repeatedly enhanced under the condition of stress field, seismic energy accumulation and release the regional characteristics of fast.
In this paper, the fractal characteristics of the gravity network in the Sichuan-Yunnan region are studied. The results show that the fractal dimension is 1.43-1.62, which means that the grid spacing of the gravity network is 30-60 km. The network has the capacity to monitor earthquakes of magnitudes larger than Ms5.0. According to the fractal characteristics of the gravity network, and combined with a calculation test, we selected 20’ (about 37 km) grid spacing to grid the gravity change data from 2010 to 2013 in the studied area. The relationship between gravity change and earthquakes is analyzed in detail. The interannual and cumulative gravity changes show that, even after the energy release of the Lushan Ms7.0 earthquake, the gravity is changing dramatically in the southwest of the Longmenshan fault zone and southeast of the Xianshuihe fault zone. The earthquake situation needs to be monitored continually.
This paper proposes a calculation method of the Bouguer gravity anomaly with stratification information of the CRUST1.0 model in the region of southeastern Tibetan plateau and compares it with the EGM2008 model. The results shows that in most places there is a little difference between the two, and that the Bouguer gravity anomaly ranged from -600 mGal to 20 mGal. The study illustrates that the precision of the model still needs to be improved.
Simulated fault parameter values are adopted to deduce the earth surface gravity changes with the combination model of vertical rectangular and the coordinate rotation theory. Numerical simulated experiments of gravity change distribution are conducted for the activities of the vertical fault disclination in a single direction and in two directions, respectively, at depths of 1 km, 5 km and 10 km. The conclusions show that the gravitational variation field shows symmetrical distribution when the vertical fault occurs with a disclination of W1 or W2 pattern based on the left point of the fault in a single direction. In addition, it appears that four quadrants show an antisymmetric distribution when a vertical fault occurs with a disclination of W3 pattern based on the midpoint of the fault. The gravitational variations field shows symmetrical distribution when the vertical fault occurs with a disclination of W1W2 pattern based on the left point of the fault. Moreover, the W2 pattern plays an important role. Gravitational variations field presents a symmetrical distribution when the vertical fault occurs with a disclination of W2W3 pattern based on the midpoint of the fault, with an obvious twisting phenomenon that is attributed to the disclination of W3 pattern in the fault vicinity. Overall, it also shows that the W2 pattern plays an important role. The earth surface gravity change is decreasing progressively when the depth of faults is increasing. However the region influenced by the vertical fault disclination is extending.
In order to further improve the calculation precision of gravity measurement in far zone terrain correction, this paper puts forward a calculation method that uses open global high resolution DEM data to calculate gravity terrain correction. This paper introduces the theoretical principle and implementation process of this method in detail, and through the comparative analysis of different examples, proves the feasibility and effectiveness of this calculation method.
The gravity recovery and climate experiment (GRACE) RL05 data from CSR is used to estimate glacier mass changes in the Himlayas from 2002 to 2014 based on mascon data in the spectral domain. The results show that the seasonal ice mass changes and long term ice mass changes can be determined from GRACE measurements in the Himalayas. During 2002-2014, after removing the impact of GIA and Hydrology, the mass change was -8.26 Gt/a, with an acceleration of -3.54 Gt/a2.
Greenland ice mass variations from January 2003 to December 2012 are recovered with the data of GRACE RL05. A combined algorithm of the de-correlated filter and Gaussian filter is constructed. The rate and acceleration of the Greenland ice mass change are computed by using linear and quadratic polynomial fitting. The results show that the melting of the Greenland ice sheet is accelerating on the whole island, with prominent ice sheet mass loss in the southern and northwest regions. During the recent ten years, after the deduction of the glacial isostatic adjustment and of leakage errors effects, the melting rate and acceleration of the Greenland ice sheet are -157.8±11.3 Gt/a and -17.7±4.5 Gt/a2, respectively. The melting mass has been accelerating significantly from 2010, 〖JP2〗with the rate of -132.2 Gt/a in 2003-2009 and the rate of -2525 Gt/a in 2010-2012. The melting rate in the Northeast tends toward stability, the melting acceleration of middle east Greenland is positive which shows the melting of ice mass in this district is slowing, but the melting of the ice mass is accelerating in the northeast and middle east after 2010.
In this paper, the associated Legendre function, with arbitrary order n and degree m Pmn(cosθ), is represented as the product sum of the coefficient E(k) and the angle (n－2k)θ′ss sine or cosine. The available value range of k is from 0 to int\[n/2\]. 〖JP2〗When the degree m is less than or equal to 2, E(k) can be expressed by the coefficient of P0n(cosθ) expansion. Otherwise, it will be a linear combination of several arrays. The given analytical expression not only helps to understand the Legendre function’s characteristics and property proof, but also can simplify its application in the related technical field.
n order to resolve the problem of how to determine the weight matrix of observations that are of different kinds and come from different systems, the empirical, satellite elevation, and Helmert variance estimation models are analyzed and studied. The data processing results show that the stochastic model of combined system relative positioning is best determined when the Helmert variance estimation model is applied. Further, the success rate of single epoch ambiguity searching and both the precision and reliability of baseline solution is improved.
Based on an explanation of the definition of GNSS system time offsets, we build a polynomial predicting model that is suitable for BDS/GPS system time offsets. Some improving measurements, such as selecting the quadratic term parameter, determining a few prominent periodic terms and choosing the weight function of observations, are applied to above model. Simultaneously, on the basis of the predicting characteristics of AR model, we build the combined time offsets predicting method of the polynomial and AR models further. 〖JP2〗The results of simulations show that the single day predicting precision of the new model is superior by 0.4ns, which is significantly better than other traditional methods
Three antenna phase center models of Beidou system (BDS) satellites are introduced. Differences and influences of these three models are analyzed with respect to precise orbit, satellite clock offset and precise positioning. Numerical results indicate that the precision of ESA model is superior to other models results. We suggest using the ESA model in BDS high precision data processing.
The double-difference method is used to determine the Beidou navigation satellite system orbit with multi-GNSS experiment (MGEX) data. This paper mainly studies the precise orbit determination (POD) strategy of Beidou satellite orbit, then discusses the basic process of determining Beidou navigation constellation orbits. Finally, based on observation data, the paper determines the three-day orbit solution of Beidou navigation constellation. The experimental results show that the internal precision of the 1D RMS of MEO and IGSO satellites in orbit determination is better than 0.2 m, the radial direction could be better than 10 cm, and outer precision is better than 30 cm| furthermore, GEO (the C05) satellite outer precision is 〖JP2〗better than 0.7 m, and the radial direction could be better than 10 cm.
The noise level of MW combination is sometimes high, causing the possibility of miss detection when using the TurboEdit algorithm. The noise property of MW is analyzed and the actual ability of cycle slip detection is evaluated. The EMD threshold de-noising method is proposed to reduce noise level of MW. To deal with the end effect of EMD, the data to be decomposed is extended by a set of data, which is formed by adding virtual noise on the time average value of MW. The thresholds of the IMFs generated by EMD of MW are estimated and used to threshold the noise. The new characteristic of de-noised MW with cycle slip is analyzed. It is found that the cycle slip will spread to neighboring data and a detection scheme based on the de-noised MW is proposed
In this paper the pseudorange multipath errors are extracted by using triple frequency data broadcasted by BDS. The results indicate that the multipath errors of pseudorange are at the meter level and that they change quickly. The multipath errors remaining after and between epoch difference can affect cycle-slip detect and repair. A new method for BDS triple-frequency cycle-slip detection and repair, which considers multipath correction, is introduced. Experiments are carried out to assess the performance of the new method. The results show that the method can control the impact of multipath errors and improve the success rate of cycle-slip repair.
In GNSS control network adjustment and position measure, It is necessary to propagate GNSS baseline vector covariance and position covariance between different coordinate system. The strict and simplified formula were derived to propagate GNSS baseline vector covariance from Gauss plane rectangular coordinate system to geodetic coordinate system, and from geodetic coordinate system to space rectangular coordinate system. The equivalent and unified propagation between GNSS baseline vector covariance and position covariance was studied. The theory analysis and test result show that the derived formula is correct, the position covariance propagation formula can replace the baseline vector covariance propagation formula, the above covariance propagation formula can be unified between space rectangular coordinate system and station rectangular coordinate system, and easy to form.
This paper introduces the measurement scheme, local triangulation network, elevation control network, target intersection measuring method and data analysis of the site survey at the Nanshan GPS and 25 m VLBI antenna of the Xinjiang astronomical observatory in 2011. Using its measurement data, we for the first time set up local tie parameters between Nanshan GPS and VLBI space geodesy technology. The measurement precision is better than 1 mm.
n order to detect PS more effectively, a method that detects PS according to several PS standard points is proposed in this paper. This method considers the stability as well as the strong characteristics of the PS scattering. In the original selection, the amplitude threshold is set according to the PS standard points. The amplitude dispersion threshold is also set according to them in the second selection. Both of the two thresholds do not need to be set manually, as they are hardly influenced by subjective factors. We conduct the PS detection experiments with 18 TerraSAR-X images that cover Macao Peninsula. The result shows that the proposed method can detect PS in the SAR image more rapidly, effectively and reliably than traditional methods.
In this contribution, an iterative algorithm of total least squares is organized for fitting spatial lines. We projected spatial straight lines to coordinate planes perpendicularly, and then total least squares (TLS) and least squares (LS) are employed to fit the plane's lines. A simulated experiment with three scenarios is designed to compare the estimated parameters and the variance of unit weight from TLS and LS, respectively. In scenario one, the error of all points is normally distributed with zero mean and identical standard deviation. In the second scenario, the error of each point is normally distributed with zero mean and different standard deviation. In scenario three, the error of point coordinate components is normally distributed with zero mean and different standard deviation. In addition, in a second experiment, a set of laser scanned data points are fitted by TLS and LS, respectively.
Users of the least squares algorithm (LS) coordinate transformation, usually focus on observation errors, but errors of the model coefficient matrix are ignored. Although total least squares algorithm (TLS) could take into account the errors of observations and the coefficient matrix, it cannot solve the problem of gross errors effectively if we start with coordinate data and observations with gross error. Through the IGG I function, which gives the right of the observation to reduce the weights of the observation with gross errors, this article presents a kind of TLS algorithm based on reweighting iteration. During the three-dimensional coordinate conversion we can deal with the observations of gross errors effectively, and it is proven through example that the TLS algorithm based on reweighting iteration can get a more accurate three-dimensional coordinate conversion parameter
The least square configuration model is analyzed in the application of small angle coordinate transformation. The least square, improved bursa, and multivariate total least square models are analyzed in the application of arbitrary angle coordinate transformation, as well as for the impacts of scale factor and rotation angle on coordinate transformation precision by experiment. It is proven that the multivariate total least square model can achieve high-precision coordinate transformation of arbitrary scale factor and rotation angle.
The ridge estimation and regularization methods are deficient because they destroy the equivalence relationship of the equation and the solution is a biased estimation. To overcome these deficiencies, an iteration method of correcting characteristic values to TLS, and its improved algorithm, are proposed on the basis of the iteration method, by correcting characteristic values to LS. The results of the examples show that the iteration method of correcting characteristic values to TLS or LS is equivalent to the general TLS or LS respectively in normal situations, and the algorithms proposed are effective but susceptible to the initial iteration value in ill-conditioned situations.
By combining the use of high-pass filter and overrun rate analysis, high-frequency signals such as fluctuations, steps and jumps can be maximally extracted based on borehole tiltmeter observations. We can quantitatively characterize these signals and test the relationships of the signals and earthquakes. To confirm the reliability of the signals ,we must exclude the factors of pressure, water and equipment. The results show that the number and intensity of high-frequency signals significantly appears with the increasing phenomenon. The abnormal duration is mostly within three months, and belongs to short-term abnormal duration. Earthquakes occurred after the anomaly ended or three months after the end of abnormal duration.
CHZ-Ⅱ is a new generation sea gravimeter, based on CHZ developing experiences. This article reports on the performance testing methods, 〖JP2〗and the analyses of the testing output, for the CHZ-Ⅱ 〖JP〗g-sensitive mechanical structure, including the stiffness of the g-sensitive elastic system, cross-coupling, and the drift of the elastic structure. The results show that the structure works well in these tests and can meet the requirements of the design.
In the case where the vertical gravity gradient is known, the g0 is the gravity acceleration value at the initial position (z=0) of the test mass. 〖JP〗In the case of unknown or not well-known local gradients, we proposed a simple equation to calculate the effective height of the test mass, which can be used in the conditions where the initial positions and initial velocities are not zero. Using these effective heights, we transfer the g-values to the zero position (z=0)| the resultant precision is better than 1 μGal.
The micro deformation monitoring system based on ground-based synthetic aperture radar interferometry is an innovative radar system that is capable of continuous and comprehensive real-time monitoring. According to the composition, working principles and the key technology of IBIS-L system, we analyze and process long time monitoring data of a large-scale hydropower slope. The deformation monitoring accuracy is compared with TM30 total station. Experiments show that, the deformation accuracy of the IBIS system is better than a millimeter and higher than the TM30 total station in the radar sight direction. Moreover, the IBIS system can achieve high resolution, high precision, and real-time deformation monitoring of large hydropower station slope for a long time.
The Cryosat-2 altimetry waveform measurements on the sea ice are retracked using the 40% threshold method in the Arctic Ocean. By combing the waveform parameters and the sea ice concentrations, the sea ice and the Lead (open water between the ice floes) are identified effectively. The sea ice freeboard is determined by along-track searching and an interpolation algorithm| it is compared with the AWI results, and the variations of the mean freeboard of the first-year and the multi-year sea ice area between 2011 and 2013 in the Arctic Ocean are given. The comparison results show good correlation in the corresponding period of each year.
The tangent plane method is often used to calculate the astronomical coordinates of the target point. However, star error can affect the the precision of orientation easily. Moreover, the method is relatively slow. In order to improve the precision of the target point, we introduce a new method of spherical triangle, which can make full use of the star information. Thus, both precision and the speed are improved.
