We use GRACE-derived seasonal variations to correct GPS vertical annual and semi-annual displacements and principal component analysis(PCA) method to filter out the common mode errors. Vertical velocities of GPS sites in the west Qinling are estimated. The precise leveling data observed since 1970 are collected, and the GPS vertical rates are employed as a priori constraints to define the reference frame. Based on linear dynamic adjustment, the present crustal vertical velocity field of the west Qinling is acquired. The results suggest that most regions of the west Qinling uplift rapidly with different rates, which is caused by the crustal shortening of the northeastern Tibetan plateau. The Liupanshan and south of Tianshui uplift at rates of 3 mm/a, the Longxi block and southern Ordos block uplift at rates of 2 mm/a and 1 mm/a, respectively. The west sections of Qinling mountains and Weihe graben show subsidence, but the Weihe graben subsides faster. The present crustal vertical movement of west Qinling implies that the current eastward extrusion of the northeastern Tibetan plateau transfers from west Qingling-Qinling mountains to Liupanshan and southern Ordos block.
Fault slip inversion can be represented by a regularization problem constrained with inequalities.Based on the improved MCMC approach, we invert for coseismic fault slip distribution of the 2015 Nepal megathrust event from GPS observations. Results show that the slip concentrates at a region eastward to the epicenter, near Kathmandu, with a maximum of 7 m. The slip errors statistically obtained by resampling model space are about 10% of slip. The seismic moment is 7.67×1020 Nm, equivalent to MW7.86, consistent with that from other research. The modeled GPS displacements agree well with the observations. Our results demonstrate that the improved MCMC method is appropriate for fault slip inversion from geodetic data and especially can give the slip errors statistically.
After the May 12th, 2008 Wenchuan MS8.0 earthquake, series hydraulic fracturing in-situ stress measuring results indicate that the orientations of maximum principal stress, in the Beichuan, Pingwu and Guangyuan areas along the northeast segment of the Longmenshan fault belt, have deflected with values of 25°~69°, as compared with regional stress field. This phenomenon is also known as in-situ stress decoupling. It is found that the decoupling of maximum principal stress orientations is caused by the right lateral strike slipping activity of the northeast segment of the Longmenshan fault belt, and has a positive correlation with the strike slipping displacement of the fault. We explain this phenomenon and investigate the mechanism of the in-situ decoupling caused by the activity of the strike slip fault. Firstly, using the co-seismic right lateral strike slipping displacement boundary conditions of the Wenchuan MS8.0 earthquake fault, the disturbed stress field generated by the right lateral strike slipping is simulated with the method of two-dimensional finite element numerical simulation. Afterwards, the effect mechanism of disturbed stress on the regional stress field is deeply analyzed, combining the in-situ stress measuring results with the disturbed stress simulated results at typical boreholes. Preliminary results show that: (1) In-situ stress decoupling, particularly, the deflection of maximum principal stress orientations induced by the activities of strike slip fault, is generated by the influence of the disturbed stress field resulting from the fault slipping on the regional stress field. (2) The deflection angles of maximum principal stress orientations have a significant positive correlation with the strike slipping displacement, under the conditions of special length and frictional strength of the active fault. (3) The deflection angles of maximum principal stress orientations are very low in Baoxing, Yingxiu and Wenchuan areas, which are basically consistent with the regional stress filed. However, they are much higher in the regions of Beichuan, Pingwu and Guangyuan, which are respectively 65°, 56° and 29°, as well as having a basically positive correlation with the co-seismic right lateral strike slip displacement of northeast segment of the Longmenshan fault belt.
In this article, we measure the tensional fracture, shear joints, and the faults developed in the Xigeda formation during the late Cenozoic. Then, we project the measurements into Wulff net with lower hemisphere, and make a rose diagram of joint and tensional fracture. The results show that horizontal principal stress is in the NNE-SSW direction during the early period and horizontal principal stress is in the NWW-SEE direction during the late period. The late stage faults are mainly strike and normal, gradually determining the structural features and landform.
The parameter of Euler vector has poor validity in a local area. An algorithm based on Elman neural network is introduced to fit the velocity field. First, the velocity of the position is computed with the parameter of Euler vector; second, the residual as the expectation of Elman neural network is again trained; finally, we determine the velocity of the position, which is equal to the sum of the results obtained by Elman neural network and the velocity of Euler vector. The data set of Shandong is employed to test the algorithm. It is shown that the new algorithm can weaken the influence of systemic error and improve the accuracy of velocity field.
The October 2010 MS4.7 earthquake in the Taikang area is related to the Taikang-Xuchang fault. The Taikang-Xuchang fault, which is in the buried structure and buried active state, has left no structural traces on the surface of the earth. In order to investigate the crustal shallow structure and the spatial distribution and activity of the buried faults in the area, three shallow reflection profiles crossing the buried faults are completed in the epicenter area west of Taikang county in October 2015. The results show that, in depths less than 1 000 meters, the seismic profile reveals five normal faults with obvious fracture features: four north dipping faults located in the south research area, and a south dipping fault, located in the northern research area, and formed opposite inclination in relationship. The profile can distinguish the faults with a depth between 75-150 m, and the fault’s fracture to Quaternary strata in a state of active tectonics. These faults may have a relationship with the Taikang earthquake.
On the basis of the traditional support vector regression machine, considering the chaotic properties of observation data, the GA-SVR combination model is built by combining the reconstruction of a phase space of training sample and the advantages of a genetic algorithm in seeking the optimum parameter. After comparing and analyzing the predicted and measured values of slope deformation, we determine that the combination model has higher prediction accuracy.
In this paper, the deformation of the landslide is regarded as the function of the time and the rainfall of every month and the temperature. Taylor series is used to determine the relationship of the deformation to the time and rainfall of every month and temperature; Taylor series is expanded to quadratic terms, and a Kalman filter model is developed to forecast the deformation of the landslide. An example of calculation shows that the fitted effect and forecast effect of the model are better, and that the model can be used to forecast the short-term deformation of the terrene landslide.
We apply the gray relational algorithm to determine the major factors directly influencing surface subsidence. The Gaussian kernel function and the polynomial kernel function are constructed, we determine an optimization of model parameters by genetic algorithm, and a prediction model of ground surface subsidence is established. The experimental data shows that: the gray relational algorithm can quantitatively reflect the degree of correlation between many factors of the system and the change of surface subsidence prediction; furthermore, the information of the gray system can be processed effectively. The reasonable combination of the weighted kernel functions can be transformed into a linearly separable map of the high-dimensional feature space by the low-dimensional linearly separable map; the genetic algorithm is simple to calculate and shows adaptive iterative optimization; the relevance vector machine model can greatly reduce the computational burden of the kernel function and the probabilistic interpretation of the process and results. The model based on relevance vector machine has good predictive effects. In addition, the accuracy of this method is better than that the precision of BP neural network, GR-SVM method.
This paper improves traditional wavelet threshold de-noise analysis from two sides. First,a new method based on Lip exponent threshold optimization is proposed by the correlation of wavelet coefficients at different scales. Second, we construct a new wavelet threshold function to deal with the wavelet coefficients. This is convenient to compute, and it overcomes the discontinuity of the hard threshold function, without the high order derivative of soft thresholding function. Finally, we process a set of discrete deformation monitoring data using the improved threshold algorithm method, showing its better de-noising ability.
A precondition for deducing the formula of forward modeling gravity anomaly profile by inclined fault (two-dimension geological body), is that the inclined fault extends to the infinite distance along the profile’s positive direction. However, no such fault exists in nature. We give the formula of forward modeling gravity anomaly profile by the inclined fault which extends to a finite distance. The range of the ‘finite distance’ is deduced. The difference between extending to infinite and finite of the two formulae is also given here.
For the ferromagnetic materials inversion problems under the effects of remanent magnetization, we propose a method based on the focus regularized inversion method based on normalized source strength. First, we use normalized source strength as measured data to make the target inversion to weaken the influence of the remanent magnetization on the inversion results. Then, depth weighting matrix and minimal support matrix are added to the inversion model of Tikhonov regularization theoretical framework to obtain the objective function. This avoids the multiple results caused by the inversion problem caused by the number of inverse parameters being greater than observational points and effectively solves the kernel function. Finally, this function calculates the optimal physical parameters by singular value decomposition. We apply the Morozov deviation principle to adaptively determine the regularization parameter in the iterative process, increasing the iterative speed and the solution accuracy.
Using interpolation and Z files, we study the precipitable water vapor (PWV) value, calculated by ground-based GPS with missing meteorological data. We compare the effects of different ways to select the appropriate method of PWV retrieval by ground-based GPS with missing meteorological data. The results show that interpolation of meteorological data in long periods using spline is appropriate; interpolation of meteorological data in short periods using singular spectrum analysis is appropriate. Using Z files is a good way to calculate PWV when the missing data accounts for a larger proportion of the original data.
With BDS real data, three linearly independent combinations of extra-wide lane (0, 1, -1), (1, 4, -5) and sub-extra-wide lane (4,-2,-3) are chosen based on triple-frequency theory with the constraints of wavelength, factor of ionospheric delay and noise, and then the code-phase combination algorithm is adopted to detect and correct cycle slip. Experimental results show that the three combinations can even detect one small slip. Considering the probability of detecting a wrong slip, the ionospheric residual error method is proposed to assist in detection. That is, original observations are used to calculate the ionospheric residual error, followed by difference of the ionospheric residual delay between adjacent epochs. The results validate that the algorithm can detect and correct all kinds of single-differenced cycle slip in real time.
Focusing on the coordinate time series captured from 7 Japanese IGS reference stations in the three years before and after the March 11, 2011, east Japan earthquake, the common mode error of this region is calculated. Furthermore, the optimal noise model of each station components before and after the earthquake are determined using CATS software, so the noise characteristics can be analyzed based on the common mode error of the east Japan earthquake. The conclusion is drawn that obvious periodicity shows in the common mode error in N, E, U direction, and the mean value in N, U direction increases 2.1 times and 1.5 times due to the earthquake. Using the spatial filtering method to eliminate the common mode error, the flicker noise in the horizontal direction is obviously weakened. Each component of IGS reference stations presents diverse noise characteristics, with no obvious regularity. The influence of the earthquake on reference station coordinate time series noise is mainly on BP, FN and RW characteristics, and the closer to the epicenter of the earthquake, the more obvious the effect will be.
The theory and algorithms of multi-GNSS precise point positioning(PPP) are studied and the convergence time and positioning precision are also analyzed in this article. We use observations from GPS, GLONASS, Beidou and Galileo and the MGEX precise ephemeris and clock from GFZ. The results show that, in static PPP, the convergence speed of Beidou is slow and the positioning accuracy of Beidou is about 5 cm in horizontal, 8 cm in vertical. The convergence speed of G/R/C/E combined PPP is faster than any single system and the positioning accuracy is close to GPS. In kinematic PPP, the average convergence time of Beidou is 110 min or more and the positioning accuracy of Beidou is about 8 cm in horizontal, 16 cm in vertical. The convergence speed of G/R/C/E combined PPP is also the fastest, whereas the positioning accuracy is not significantly improved compared to GPS. Under the circumstances of higher cut-off elevation, the positioning errors of GPS are larger than multi-GNSS, since multi-GNSS can observe more satellites than GPS.
A time transfer experiment based on the BDS precise point positioning (BDS PPP) technique is carried out using WHU (Wuhan University) 5 min precise satellite clock products. Experimental data come from the observations of four stations that belong to Gansu continuously operation reference station system. In order to verify the accuracy of time transfer based on BDS carrier phase (BDS CP), this paper compares the difference between BDS CP results and GPS CP results. The experimental results demonstrate that the RMS of the difference between BDS CP and GPS CP is about ±0055 ns. Since the accuracy of time transfer based on GPS CP is up to 0.1~0.2 ns, it can be inferred that the accuracy of time transfer based on BDS CP is roughly equal to GPS CP.
A spatio-temporal ZTD modeling method based on principal component analysis (PCA) is proposed. Based on this modeling method, three regional spatio-temporal ZTD models of Hong Kong, Yunnan province and China mainland are established using daily ZTD observation data obtained from the GNSS continuous operation reference stations. The test results show that the accuracy of the regional spatio-temporal ZTD models is significantly higher than that of the Saastamoinen, EGNOS and UNB3m models. Moreover, the proposed PCA spatio-temporal ZTD modeling method has advantages such as simple modeling process, less model parameters and greater convenience.
Measurment receivers are an essential part of research satellite navigation system, but expensive and unchangeable of built-in algorithms limit its use and development. The architecture of measurement receivers are overviewed, analyzed the BD970 OEM board with ARM7 architecture card of computer and its external communication mechanism, designed principle prototype of measurement receiver based on the card based on ARM7 architecture computer which can obtain and decode real-time data from BD970 OEM board. For its correctness and reliability of data, will BD970 OEM board with Trimble refused NetR9 using zero-base line validation. The correctness and reliability of data are verifird by using zero-base line between BD970 OEM board and Trimble refused NetR9. Type experiment results show that the design of the measuring receiver principle prototype can be continuous and stable operation, and can work out accurate and reliable real-time observation and ephemeris data, preliminary validation of principle prototype is realized.
We found that observed-data drifts are common phenomena by analyzing the multi-year temperature variation trends of 15 fluid observation wells in Qinghai province. The drift of 6 wells exceed 0.01 ℃/a, which is the limitation in the observed network. There are no correlations between temperature drift, water level and air-temperature, and no rule is found in drift distribution. We cannot draw conclusions about the relations between temperature drift, regional stress and strain status. The infection point of temperature trends are generated by the earthquakes or changes the observed positions in Yushu and Geermu wells, which implies that the observation system (instrument & sensor) is not the unique reason for temperature drift. To reject the drift by changing the means of observation, by comparing two different thermometers, is not possible.
Characteristics of water level co-seismic responses and post seismic effects induced by the MW8.1 Nepal earthquake are analyzed, and the adjustment state of stress is calculated using co-seismic water level changes. The results show that the main types of co-seismic response and post seismic effects are oscillation and rise, respectively. The north-south seismic belt is the main area, with more adjustment induced by the MW8.1 Nepal earthquake, related to the co-seismic adjustment of stress. The stresses on the border of Gausu province and Qinghai province, Yunnan, and the borders of Sichuan, Chongqing and Guizhou enhanced obviously. In 2 years after MW8.1 Nepal earthquakes, four earthquakes occurred in the border of Gausu and Qinghai provinces, and in Yunnan. This indicates that the area of the co-seismic enhancement of stress inverted by co-seismic water level might have certain indicative significance to future earthquakes.
Our research is based on the airborne gravity data from GT-2A gravimeter and the high-precision ground gravity data collected in two areas, marked as A, which is flat, and B, which is steep. We calculate the internal precision of GT-2A gravimeter by network crossover adjustment, and evaluate its external precision by comparing the continuation results of airborne and ground gravity data. The results show that the inner precision of GT-2A gravimeter is less than 1 mGal, while its external precision is less than 2 mGal in zone A, and 3 mGal in zone B.
