Post-Seismic Relaxation Effect And Aseismic Creep Of Fault Zone Based On Continuous GPS Coordinate Time Series

The Longmenshan fault zone has experienced a magnitude 8.0 Wenchuan earthquake(2008.5.12)and a 7.0 grade Lushan earthquake(2013.4.20)in five years.Together with its special geographical location,the area has become a key area for earthquake research.And found in earthquake research,The aseismic creep are a double-edged sword.It has the potential to eliminate an earthquake threat that is tending to the fault zone,and it can cause stress transfer to trigger a normal earthquake.Based on the above two points,in this paper,the coordinate sequence of 12 GPS stations on the upper and lower plates of the Longmenshan fault zone is used to study the post-seismic relaxation effects after the Lushan earthquake and the aseismic creep of the Longmenshan fault zone during 2012-2015.The post-seismic relaxation effect and the aseismic creep of the fault zone have strong theoretical and practical significance for understanding the post-seismic deformation mechanism,the dynamic process of the fault zone and the impact of the aseismic creep on the earthquake.The main research work is as follows:(1)For the GPS coordinate time series of 12 stations,there are 156 gross error data are eliminated based on the IQR criterion,and the offset of 101 is removed based on the least squares criterion.The cubic spline interpolation method and the multi-point cubic spline interpolation method are used to supplement the data with continuous missing less than 3 days in the coordinate time series and the data with continuous deletions greater than 3 days.(2)For the pre-processed GPS coordinate time series,the optimal noise model is analyzed based on the maximum likelihood estimation method and the BIC numerical Analysis,and the fitting effect is verified by the spectrum analysis method.The results show that the optimal noise model in different directions of each station is white noise + flicker noise,and the model is used to fit the coordinate time series to eliminate linear items,periodic items and offset items.(3)After that,in this paper,the principal component analysis is carried out on the residual coordinate time series after eliminating the trend item,the period term and the offset to extract common mode error.For the filtered residual coordinate time series,on the one hand,the post-seismic time series of the QLAI,SCTQ and YAAN stations near the Lushan earthquake epicenter are selected for analyzing post-seismic relaxation effect.On the other hand,it directly performs spatial response analysis to study the aseismic creep of the Longmenshan fault zone.The results show that the post-seismic relaxation effect of the Lushan earthquake is weak,reflecting the low viscous coefficient of the Longmenshan fault zone.It is not necessary to consider the relaxation correction when establishing the site coordinate time series fitting model.During the period from 2012 to 2015,two aseismic creep occurred in the Longmenshan fault zone.The strike of the Longmenshan fault zone is NE-SW and the aseismic creeping movement mode is tendency slip and thrust slip,and its strike is NW-SE.The aseismic creeping event before April 20,2013(Lushan Earthquake)may accelerate the Lushan earthquake.