Upper-crustal radial anisotropy beneath the Weifang segment of the Tanlu fault zone using the modified multicomponent frequency-Bessel transform method
The Weifang segment of the Tanlu fault zone is located in the middle part of the Tanlu fault zone,which has a complex geological structure and presents a structural pattern of"two garbens and one horst".In comparison to other areas of the Tanlu fault zone,the seismic activity of the Weifang segment is relatively weak,and it is considered a seismic gap with unclear potential for a future large earthquake.Previous studies on this area are limited to velocity structure and azimuthal anisotropy structure,with little research conducted on the radial anisotropy structure of the upper crust.Therefore,investigating the velocity model and radial anisotropy structure of the upper crust in this region can help us better understand the deformation characteristics of the shallow crust(＜10 km)in the Weifang segment of the Tanlu fault zone and evaluate the likelihood of earthquakes.Using the ambient noise data recorded by 302 short-period stations employed in the Weifang segment in 2017,we extracted the fundamental and higher-mode dispersion data of Rayleigh wave and Love wave of four sub-arrays in the southeast of the Weifang segment based on the modified multicomponent frequency-Bessel transform(MMFJ)method.The velocity of the SV wave and the SH wave as well as the radial anisotropy are obtained by further inversion of these dispersion data.Numerical experiments show that the addition of higher-mode dispersion data can reduce the non-uniqueness of the inversion and better constrain the radial anisotropy of the shallow crust.The radial anisotropy results from field data indicate that the four sub-areas in the Weifang segment of the Tanlu fault zone exhibit similar deformation characteristics.At depths of 0～2 km,the radial anisotropy is negative(VSH＜VSV),which may be mainly controlled by the effect of the vertical fault structure in the Weifang segment.At depths of 5～7.5 km,the radial anisotropy is positive(VSH＞VSV),which may be related to the horizontal deformation structure caused by the early crustal extension tectonics.At depths of 2～5 km,the radial anisotropy structures in the four sub-areas are different,but the overall trend is from negative to positive.This may be due to the fact that the 2～5 km depth range is not only controlled by the fault structure but also influenced by the horizontal sedimentation structure,leading to a more complex radial anisotropy structure.
万方数据
维普
