Velocity structure of the Xishancun landslide in Li County,Sichuan Province,explored by HVSR method
The HVSR(Horizontal to Vertical Spectral Ratio)is the Fourier spectral ratio of the horizontal and vertical components of ambient seismic noises,which is often used to study near surface velocity structures for areas with small topography.However,it is necessary to evaluate this method in large topographic area.In this study,we will apply the HVSR method to obtain velocity structures of the Xishancun Landslide in Sichuan Province.We first transform three-component seismic waveforms in the ENZ coordinate system to the LQT coordinates,in which the L component is perpendicular to the landslide surface.We then calculate HVSR curves with 2-hour long seismic noises under these two coordinate systems.Comparison of the two HVSR results suggests that the peak of HVSR curves in the LQT coordinate system bears better information on underground structures.We then invert the HVSR curves to obtain one-dimensional shear wave velocity structures of the landslide and bedrock beneath 29 stations.The shear wave velocity of the landslide ranges from 50 m·s-1 to 1000 m·s-1 and the thickness ranges from 23 m to 130 m.Our results show a lower shear velocity layer with a thickness of 10～20 m lies at a depth of 40～120 m for stations on the west side,suggesting a weak shear strength and potential sliding dangerous zone.After coordinate transformation to the observed data,the HVSR method can obtain reliable velocity structures by using short-term observational data,which provide important information for landslide volume estimation,weak zone identification,and hazard assessment.
Xishancun landslide in Li CountyHVSR methodS-wave velocity structuresAmbient seismic noises
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