Crustal Deformation On The Central And Southern Segments Of The Tanlu Fault Zone Based On Anhui CORS Measurements

Global Navigation Satellite System(GNSS)can not only be used for positioning,navigation and timing,but also plays an important role in the crustal deformation monitoring and geophysical inversion.With the development of the Crustal Movement Observation Network of China(CMONOC)and the Continuously Operating Reference Stations(CORS),we could utilize GNSS observation data to achieve higher-precision inversion of regional surface deformation and fault characteristics.The research object of this paper is the central and southern segments of the Tanlu fault zone,which crosses multiple tectonic blocks from north to south with complex internal structural and earthquake disasters occurred frequently since the Quaternary.In the past few decades,several large earthquakes have occurred around the Tanlu fault zone,such as the Wenchuan Ms 8.0 earthquake in 2008 and the Tohoku-oki Mw 9.0 earthquake of Japan in 2011.Therefore,the kinematic properties of the Tanlu fault zone may be affected by the far-field postseismic deformation of these earthquakes.There is a lack of studies on crustal deformation and strain accumulation in the region,and the seismic risk is unknown in this densely populated area.The work of this paper includes three parts.First,use the observation data of AHCORS to obtain a high-precision velocity field under the Eurasian frame,and then combined with the public CMONOC velocity field data.Second,the multi-scale spherical wavelet and least-squares collocation method are used to calculate the strain rates on the central and southern segments of the Tanlu fault zone.Through the results of strain rates of principal strain rates,dilatation rates and maximum shear strain rates,the distribution characteristics in local areas are discussed.Third,based on velocity field vector data,negative dislocation model is used to invert the distribution of locking degree,locking depth and slip rate deficit of the central and southern segment of the Tanlu fault zone,so as to analyze and evaluate the seismic risk in the study area.The main research results of this paper are as follows:(1)Use GAMIT/GLOBK software to solve the observed data of AHCORS in recent 6 years from January 1,2013 to June 30,2018.The coordinate time series and velocity field under the International Terrestrial Reference Frame 2008(ITRF2008)are obtained.In order to more accurately analyze the motion characteristics of the region,the velocity field under the ITRF2008 framework is converted to the Eurasian framework.The results show that the speed of AHCORS reference station under the Eurasian framework mainly moves to the east by south direction.According to the results of velocity profiles,the velocity parallel to the profile is-0.76～-0.35 mm/a,and the velocity perpendicular to the profile is-0.44～-0.29 mm/a.The motion characteristics of the central and southern segment of Tanlu fault zone are dextral and compression.(2)The multi-scale spherical wavelet and the least square collocation method are used to calculate the strain parameters of the central and southern segments of Tanlu fault zone.The results show that the least square collocation method shows that the principal strain rate near the Weifang-Tancheng section on the central and southern segments of the Tanlu fault zone is almost zero;The Tancheng-Jiashan section is the high value area of the principal strain rate.Bounded by the Tanlu fault zone,the west side is characterized by near E-W and N-S stretching,and the east side is characterized by NE-SE or NW-SE stretching;The principal strain rate of Jiashan-Tongcheng section is relatively small,and its east side is characterized by near E-W tension,and its west side is dominated by near N-S compression.The results of principal strain rate of multi-scale spherical wavelet method are similar.For the dilatation rates,the least square collocation method shows that the maximum value appears in the west of Tancheng-Jiashan section,which is in the state of expansion with a size of 3.78×10;~8/(6.The results of multi-scale spherical wavelet can reflect the characteristics of strain accumulation in a smaller region.In the west of Tancheng-Jiashan section,the north is in the state of compression,while the south is in the state of expansion.For the maximum shear strain rate,the least square collocation method shows that it on the central and southern segments of the Tanlu fault zone is smaller than that on both sides of the Tancheng-Jiashan section and the east of Tongcheng.The results of multi-scale spherical wavelet method also show approximate characteristics,but the size is slightly larger than that of least square collocation method.(3)The AHCORS velocity field under the Eurasian framework is fused with the CMONOC velocity field to obtain a"new"velocity field.Taking the GPS velocity field vector data as constraints,the activity characteristics of the central and southern segment of the Tanlu fault zone are inverted by the negative dislocation model.The results show that compared with Tancheng-Jiashan and Jiashan-Tongcheng segments on the central and southern segment of Tanlu fault zone,Weifang-Tancheng segment has higher locking degree,deeper locking depth and higher slip rate deficit,which means that strain accumulation is more likely to occur in this segment.In general,the strain accumulation rate in the Weifang-Tancheng segment on the central and southern segments of the Tanlu fault zone is faster,and the possibility of earthquake risk is greater.In general,the recurrence interval of long-period large earthquakes is the main feature of the late Quaternary activity on the central and southern segments of the Tanlu fault zone.