The anomaly change of PWV after earthquakes is analyzed through the change of PWV time series in the epicenter of the east Japan, Wenchuan, and Yushu earthquakes. First, we analyze the change of MODIS PWV sequence in the epicenter and the change of radiosonde PWV sequence near the epicenter before and after the earthquake. Then, based on the high correlation between GNSS ZTD and PWV, for GNSS PWV replaced by GNSS ZTD, we analyze the change of GNSS ZTD sequence of IGS sites around the epicenter. It is found that after the earthquake, the change of PWV in or near the epicenter is abnormal, and the closer the distance, the greater change of PWV. For PWV accumulating continuously, the precipitation occurs after the peak of PWV.
Based on the sorting and processing of multi-periods absolute and mobile gravity data of seismic gravity monitoring network, dynamic variation results of the gravity field in different time and spatial domains are calculated for the Jiangsu-Anhui segment of Tan-Lu fault zone. Dynamic variation results of gravity field are decomposed into gravity variation details of different depth levels using the method of wavelet multi-scale decomposition. We discuss the transverse variation of different depth levels and the vertical variation of different time scales combined with regional geological tectonic features. The results indicate that the variation of regional gravity is mainly caused by density change or tectonic activity from the middle and upper crust. The distribution of tectonic activity intensity is not uniform and composed of many sub-sections along the Jiangsu-Anhui segment of Tan-Lu fault zone, influenced by the intersection with the deep fault. The tectonic activities of deep active fault zones have certain control effects on local gravity variations, such as Huaiyin-Xiangshuikou fault and Chuhe fault, because of the obvious gravity gradient zone along the fault zone. In the dynamic variation of wavelet details graph, Tancheng-Sixian section of Tan-Lu fault zone and Huoshan-Lu’an area of Dabieshan orogenic belt, and Liyang-Zhenjiang area of Jiangsu province, have gravity variation zone turns or abnormal areas, but the strength of gradient zone is not high, considering the deep tectonic background of intersection with several deep faults.
We calculate the lithospheric bottom mantle convection stress field of southeastern Tibetan plateau using 11~36 spherical harmonic coefficients of gravity model EGM2008. Meanwhile we collect and organize the focal mechanism of 1 131 earthquakes that occurred from 2000 to the present in southeastern Tibetan plateau. The current seismogenic layer stress and stress field before Lushan earthquake are calculated by the damping regional stress tensor inversion. We further analyze the correlation between the two kinds of stress fields, then discuss the relation between mechanics coupling situation and strong earthquakes in different regions. The results show that: (1) Most of southeastern Tibetan plateau is located in the coupling and decoupling intermediate zone. Coupling zones distribute on the basis of block; the eastern south China block has strong coupling, and the coupling phenomenon also exists in parts of the northern Tibet block, Bayan Har block in the northwest, and southwest Yunnan block. The decoupling mainly occurs in Songpan-Ganzi block, connecting with the strong coupling south China block and Longmenshan fault zone, which is their boundary. (2) We analyze the seismogenic mechanism, then propose that the border zone, of strong and weak coupling relation between mantle convection stress and seismogenic layer stress, presents a high seismic risk. The current coupling situation shows that Longmenshan fault zone is still in the large varying gradient area of coupling intensity level, and has conditions to accumulate energy and develop earthquakes. Other dangerous areas are: Mingjiang fault zone, Xianshuihe-Anninghe-Zemuhe fault zone, the Red river fault zone, Nantinghe fault zone and their neighboring areas.
Aiming at the problem that the regional crustal vertical motion model cannot be established for a small number of stable level points, we propose a method for establishing a regional crustal vertical motion model using GNSS and level fusion. At first, some stable level points and GNSS points are used to found the original vertical crustal movement model. Then, the final points are chosen by the analysis of the difference between the result of the original model and the result for GNSS points and level points. Finally, the vertical crustal movement model is fitted with the function. An actual GNSS data and level data set of Shandong province is employed to test the new algorithm. It is shown that the new method overcomes the shortcoming that the vertical crustal movement model is not founded with few level points, and also that it improves the accuracy of the vertical crustal movement model.
We collect leveling observation data in 1980, 2005 and 2015 to study the present crustal vertical movement of Jiangsu-Anhui area. We conduct qualitative and quantitative analysis based on the vertical deformation rate field in the research area.Then, we undertake reasonable interpretation and analysis about the vertical movement field. Combined with previous research results of the research zone, the relation between the present crustal deformation and seismic activity and dynamic mechanism of research area is explored to provide certain basic data in regional seismic risk and geodynamic study.
This study shows the optimization by using the particle swarm optimization algorithm combined with the dislocation model. Three-dimension slip velocity of the Qilian mountain fault is inversed using GPS data observed in north-east margin of the Qinghai-Tibet plateau during 2001-2004 and levelling data in 2000-2006. The results show that multiple data joint inversion can more reasonably grasp the motion characteristics. The particle swarm optimization algorithm can compute three-dimension slip velocity of the Qilian mountain fault effectively. This algorithm will have broad application prospects in geodetic inversion.
We obtain clear high-resolution seismic time profiles, revealing the distribution location, structural morphology and deformation pattern of the Sumatou fault. We use the methods of ‘three small, three high,two tricks’ , combined with static correction, noise attenuation of multi-domain and multi-method, and fine velocity analysis. The exploration results show that the regional structures are mainly thrusting structures; that is, between the recoil faults and the thrusting faults, pop up structures or thrusting triangular structures are often formed, which have obvious wedge-shaped characteristics in seismic profiles. The fault strike is mainly NE, the fault tends to be SE, and some tend to be NW.
In this paper, we carry out wavelet transform of natural earthquakes, blasting and collapse. The support vector classifier LIBSVM multi-class pattern recognition method is used to classify Shannon entropy characteristics, and the recognition rate is between 80% and 95%. The results show that the method of classification of waveform features by LIBSVM can be used to identify natural earthquakes, blasting and collapse.
We analyze the seismicity characteristics of Xiangjiaba reservoir region before and after the impoundment, as well as the relationship between the seismic sequence in the last segment and the reservoir water level, combined with the lithological and structural features of the epicenter area. We find that the earthquakes occurred in the last segment of Xiangjiaba reservoir are structural reservoir-induced earthquakes. These earthquakes are distributed in a NW direction. Although no obvious surface rupture zones are formed, there may be hidden faults 2 km below the surface. This area is located in the middle section of the Mabian-Yanjin fault zone, and shows very low levels of natural seismic activity prior to the impoundment of reservoir. However, after impoundment, the frequency and intensity of seismicity increased in this area.
This paper proposes an improved correlation weighted stacking filtering method. The method takes into account the overall noise level of the GPS station position residual series, which helps to suppress the adverse effects of the site’s own noise and residual gross error on the CME calculation, and uses the correlation coefficient as the weighting factor to generate a good spatial response. Furthermore, the feasibility of the method is analyzed using the GPS time series data of 8 CMONOC stations. The analysis results show that the RMS improvement rate of the method is about 20% relative to correlation weighted stacking filtering, has better performance, and can extract CME more accurately.
Observations made up of B1 and B2 signals in the MW combination are greatly affected by noise error and ionospheric delay error, so we propose to use the observed values of B2 and B3 signals to constitute the ultra-wide lane MW combination of weak ionosphere. The joint modified MW combination and the two geometry-free phase combination (1, 0, －1) and (0, 1,－1) of the two weak ionospheres are used for cycle slip detection and repair experiments. The experimental results show that MW pseudorange noise is reduced and detection accuracy is better, which is conducive to the detection and repair of the cycle slip.
In the middle-long baseline solution, the atmospheric error between stations cannot be completely eliminated by double difference, which affects the fixing and precision of ambiguity. After obtaining the wide lane ambiguity, this paper uses a Kalman filter algorithm to estimate the ambiguity of L1 and B1 fundamental frequency, and uses LAMBDA algorithm to determine the ambiguity. Taking the medium-long baseline measured data of three-dimensional mobile deformation platform as an example, several long and medium baselines under three modes of GPS, BDS and GPS/BDS are calculated. Overall, the precision of GPS/BDS integrated system is improved to a certain extent, as compared with single GPS and single BDS. The fixing and correction rates of each baseline of GPS/BDS integrated system are better than 82.08% and 81.53%, the precision of X, Y, Z can reach 15.4 mm, 15.9 mm and 20.1 mm, and the 3D direction accuracy can be better than 30.0 mm. In 20.8 km and 46.6 km baselines, the median errors can be better than 18.8 mm and 22.5 mm respectively, and the relative median errors are better than 1/71.9 and 1/60.1 respectively.
To compensate for the current existing single-epoch algorithm to resolve ambiguity, which is only suitable for short baselines, we propose an algorithm with dual-frequency GPS observations to achieve medium and long baseline single-epoch ambiguity fixed according to the error propagation rate. Then, the ambiguity search space is determined according to the accuracy. Firstly, the linear constraint condition between the double-difference ambiguities is obtained by the ionospheric constraint method. Secondly, the approximate coordinates of the monitoring station in the deformation monitoring are used to obtain the approximate ambiguity. Finally, the search space is obtained according to the accuracy of the observational data, and then we search for and fix the ambiguity. The experimental results show that the method can fix the ambiguity of single epoch under medium and long baseline, and it has certain reference value for real-time deformation monitoring.
In order to investigate the optimal estimation strategy of inter system bias(ISB), we estimate ISB in static PPP test based on five handling schemes, including gaussian white noise, 20 min piecewise constant, 30 min piecewise constant, 1 h piecewise constant and 2 h piecewise constant. The observation data of the GPS, BDS, GLONASS and Galileo is provided by IGS and the precision satellite clock and precision orbit products are provided by GFZ. We obtain the coordinate deviations in three directions of east (E), north (N) and up (U) directions respectively, using these data to analyze the convergence time and positioning accuracy of multi-system fusion PPP under different ISB solution strategies. The results show that, in multi-system combination PPP, the 20 min piecewise constant estimation strategy performs best in consideration of the strength of the observed model and the stability and reliability of the positioning results. The convergence time is about 30 min and the positioning accuracy is better than 2 cm, 1 cm and 5 cm in E, N, U directions, respectively.
We continuously receive ten days of CNES real-time broadcast data stream information in the state space representation and analyze the integrity of real-time data stream up to 91.769%. Simultaneously, we analyze the accuracy of real-time precision satellite orbit and clock error, which we recover by broadcast ephemeris. The three-dimensional positional accuracy of real-time data stream broadcast by CNES is better than 4.5 cm, and the clock error accuracy is better than 0.09 ns. Then, using the recovered satellite orbits and the clock error, ten-day observation data of ten IGS stations are used to perform precise point positioning calculations. It is concluded that the RTPPP based on the SSR information can achieve 23 min convergence. With a positioning performance of 10 cm accuracy, the single-day solution 3D point accuracy is better than 3 cm.
In this paper, ellipsoidal constraints are used to describe the bounded prior information of observation vectors and parameters, which are incorporated into the measurement adjustment model. A new adjustment criterion is established to suppress discomfort. Simulation examples and ill-conditioned data of the distance-measuring network are given to show the advantages and disadvantages of ellipsoidal constraint algorithm and other methods，and verify the validity of the bounded ellipsoidal uncertainty adjustment method in dealing with ill-posed problems.
The accuracy of solution for ill-posed model can be significantly improved by introducing the reasonable equality constraint between the adjustment parameters. However, the essence is to improve the ill-posedness of model by introducing regularizated parameters, which results in the change of structure of the observation equation. Therefore, the solution of ill-posed model with equality constraints is biased and its residual is amplified accordingly, which results that the unit weight medium error estimated by traditional formula is biased. In this paper, the unbiased estimation of unit weight medium error of constrained regularizated solution is derived according to mathematic expectancy formula of residual matrix in quadratic form, which is based on the unbiased estimation of unit weight variance for regularizated solution. The correctness of the formula is verified by numerical example and ill-posed trilateration network example and results show that the accuracy of unit weight medium error estimated by formula derived by this paper is better than traditional formula.
The basic methods for analysis of underground seismic fluid data include averaging, detrending changes, spectrum analysis, custom function fitting, wellbore water temperature gradient curve drawing, etc. There is some professional software to carry out these methods. However, these software have poor adaptability, and are challenged to deal with various types of data as different boreholes, different well-aquifer systems, and so on. In this case, the professional mathematical tools reflect their superiorities. MATLAB is number one in numerical calculations of mathematical applications, which has advanced technical computing languages and interactive environments for algorithm development, data visualization, data analysis, and numerical computation. In this article, the implementation and examples of these analyzing methods are shown.
We collect and sort observation data of water pipe inclination at Yunxian station and filter out the fixed frequency component of solid tide. We then eliminate the rain interference, construct a linear equation of monthly precipitation and monthly tilt increment, thus obtaining the residual error between the actual measured value and the theoretical value. The results show that the starting or ending time of the two-component anomalous change in the tilt observation is of certain significance to the time of future earthquakes, within 500 km around the station. In particular, when the residual quantity is greater than 1 times, the mean residual quantity anomaly starts within one to six months, earthquakes of magnitude 5 or more will occur within the range of 200 km from the station, and earthquakes of magnitude 6 or more will occur within the range of 500 km from the station. The results of the forecast efficiency test show that the method has good earthquake reflection effect on earthquakes of magnitude 5 or more in Yunnan region, and can provide a quantitative criterion for the analysis of medium-short impending earthquake trends in this area.
The paper studies the correlation coefficient, short-period (less than 128 min) atmospheric pressure coefficient, and time-frequency spectrum of volumetric strain of Qingdao station by correlation analysis, regression analysis and cross wavelet transform. The results show that short-period atmospheric pressure can influence volumetric strain of Qingdao station (between 16 and 128 min). High-frequency correlation coefficients, whose periods are less than 16 min, are small and increase with period. Low-frequency(more than 16 min) correlation coefficients are large and variations are small. Low-frequency (between 16 and 128 min) atmospheric pressure coefficient is (3.5~3.6) × 10-9/hPa. When the periods are 16~64 min, the variations with time of atmospheric pressure coefficients are smallest. Cross wavelet transform can reveal the time-frequency spectrum correlation coefficients, which can meticulously study the correlation of atmospheric pressure wave and volumetric strain of different periods.
This paper presents an automatic detection method for microseismic signals based on wavelet cross-correlation technique. In this method, the complex Morlet wavelet is used to transform the seismic waveform at a specific scale, the angle correlation is analyzed, and the reasonable similarity threshold is set to automatically detect small earthquakes. By testing the 30 minutes waveform after the ML4.8 earthquake in Changji, Xinjiang on May 1, 2018, it is found that 11 seismic sequences are detected by this method, and the P-wave arrival results of the detecting station are given. By comparing with the unified cataloguing results of the earthquake in the center of the China Seismic Network, there is no missed detection, and the difference of the seismic wave arrival time of the false check is basically within 1 second. It is considered that this method is feasible for seismic sequence microseismic detection.
We design an automatic collection system of railway roadbed subsidence data. The system adopts static force level gage as the collection unit of railway roadbed subsidence data. Using LoRa wireless communication technology, and a low power STM8 series single chip and SX1278 RF transceiver, the Contiki operating system and its own Rime protocol stack are transplanted in the IAR environment to complete the multi-hop transmission of Mesh network. The collected railway subgrade settlement data is formed into a visual monitoring interface to realize the remote, low power consumption and reliable wireless transmission of the existing railway subgrade settlement data.
