Research On The Detection Theory And Method Of Crustal Abnormal Deformation Information Based On GNSS

The abnormal crustal deformation information studied in this paper mainly refers to the crustal deformation phenomena which are different from the long-term movement trend of plates or faults and related to the tectonic movements such as earthquakes and volcanic eruptions,and these phenomena are often manifested as the non-linear movement of the crust.The slow slip event in the subduction zone releases huge energy,which is one of the main factors causing geological disasters such as earthquakes and volcanic eruptions.Therefore,the detection and analysis of crustal deformation information,such as slow slip,are helpful to explore fault slip mechanism and evaluate regional seismic risk.In this paper,on the basis of the detection of crustal deformation information and the analysis of crustal deformation characteristics in the abnormal area,the noise characteristics analysis,spatiotemporal filtering and the detection theory and method of crustal deformation information based on GNSS coordinate series are studied.Then,North China,Beijing-Tianjin,Sichuan-Yunnan,Akutan,Cascadia and Manawatu are selected as experimental areas,and GAMIT/GLOBK,QOCA,CATS and Fakenet are used to realize data processing and simulation.The main work and conclusions are as follows:(1)The influence of mass loading on the noise characteristics of GNSS time series in Beijing-Tianjin area is studied with the help of geophysical data.After deducting the mass loading,the spectral indexes of N and E directions show the trend of increase and decrease;the linear velocity variation in U direction is the most obvious,and Beijing is stronger than Tianjin;the velocity uncertainty in N and U directions changes greatly,with average change rate of 45.53%and 37.85%,respectively.(2)For small scale area,the filtering characteristics of stacking filtering,principal component analysis and independent component analysis are studied.The results show that the three methods can filter effectively.After filtering,the standard deviation of GNSS coordinate series is reduced by 28%?47%,and the extracted common mode error correlation coefficients are all greater than 0.7.The filtering effect of stacking filtering is similar to that of principal component analysis,but the phenomenon of over filtering is obvious.Independent component analysis avoid over filtering,and the region characteristic of common mode error is stronger.(3)To solve the problem that common mode components are difficult to determine,a method based on contribution value and spatial response is proposed.The results show that the common mode errors in the three directions of N,E and U are all fractal white noise,with a common period of 58.07 days.The spatial response shows the regional distribution characteristic in Yunnan is stronger than that in Sichuan.In addition,three non-linear signals are detected in the horizontal direction.Based on the analysis of seismic data,it is concluded that they may be related to strong earthquakes.(4)A method for detecting the transient aseismic creep information by combining independent component analysis with relative strength index is proposed.Independent component analysis is used to improve the signal-to-noise ratio of coordinate series,avoiding the influence of over filtering,and the relative strength index is taken as the oscillation index,which is conducive to the detection of abnormal fluctuations.The simulation results show that the method can detect abnormal crustal information effectively,which can not only improve the signal-to-noise ratio of coordinate time series,but also determine station distribution of the abnormal information.(5)Slow slip information is detection by multi-channel singular spectrum analysis.Aiming at the problem that the starting and ending times of abnormal information are difficult to determine,the scheme of selecting the hysteresis window based on the characteristics of slow slip and the existing results is discussed.The signal property is clarified,and the starting and ending times are determined.A method is proposed to normalize the signal amplitude to spatial response,the spatial distribution of slow slip is clarified,and the sliding characteristics of fault zone are revealed.By comparing with independent component analysis and principal component analysis,it is confirmed that multi-channel singular spectrum analysis has obvious advantages in determining the time and spatial distribution of abnormal information,and can reveal the sliding characteristics of fault zones.(6)Based on the detection results of abnormal crustal deformation information,the changes of crustal deformation characteristics in Sichuan province are studied to provide a scientific basis for seismic risk assessment.The results show that the main strain rate field,the maximum shear strain rate field and the surface expansion rate field of the Longmenshan fault zone are obviously weakened during 2014?2016 compared with2009?2013.The surface compression strain rate decreases from-7.18×10^-8/a to-3.27×10^-8/a,and the maximum shear strain rate reduces by three quarters.On the contrary,the compression strain rate of Anninghe fault zone increases significantly,with the maximum value of-1.04×10^-7/a.The maximum shear strain rate of Xianshuihe fault zone increases,and the range is expanded.In addition,the changes of baseline length of Longmenshan fault zone and Anninghe fault zone further confirm the above conclusions.