The Comparative Study Between Microtremor Survey Result And Drilling Record In Houhu Area,Wuhan

With the rapid development of urbanization,the city scale is more and more big,the balance of the original natural system in city might be affected by a certain,and urban geological hazards might be induced.It is necessary to obtain underground three-dimensional structure of city,so that urban geological hazards could be prevented and controlled.In the other hand,underground structure of city is an important factor in seismic hazard.The thick and loose sedimentary formation might is sort of amplification for seismic wave.So it is necessary to obtain underground three-dimensional structure of city to provide ground motion parameters for aseismic architectural design.Borehole detection is the most accurate and reliable measure to obtain velocity structure underground.However there is shortcoming such as the high costs and low efficiency.Traditional geophysical exploration has highly developed theory and application,but in the city there is too much interference and limiting factors.So in recent years,microtremor survey method has attracted more and more attention for its nondestructively detecting,rapid economic and high efficiency.This article selects Wuhan Houhu Lake area as the study area.Principle of microtremor survey method,research progress and application status at home and abroad has been summarized and expounded detailedly.Based on the collection and analysis of borehole data of Wuhan Houhu Lake area,the relationship between shear wave velocity and soil depth is carried out and the regression parameters are provided.Simultaneously,microtremor survey gets done near the boreholes.Then comparison study between microtremor survey result and borehole data has been done,and the reliability and precision of microtremor survey method has been evaluated.By summarizing the comparison study,and widely microtremor exploration in study area,characteristics of overburden layer thickness distribution is carried out.Research shows that:(1)Shear wave velocity and depth of soil are highly correlated in Houhu Lake area.Overall the optimal regression formula between shear wave velocity and depth is Vs=150.7+ 3.914H+0.01058H2,and the correlation coefficient is 0.7508.(2)The precision of microtremor exploration in Houhu Lake area is quite high.In contrast with the borehole data in study area,the offset value of thickness of overburden layer is between 1.6-6.3m,and the error is less than 15% in principle.The offset value of the equivalent shear wave velocity obtained by microtremor exploration is no more than 17.77m/s,and the error is within 11%.(3)The inversion for the overburden layer thickness in Houhu Lake area shows that the thickness of overburden layer is mostly between 25 to 55 m.Cover the thickest in Tianhe airport and Jintan lake village,which is up to 90 m.The thinnest covering layer is distributed in north of Fenghe hill and northeast part of study area – around the Hengdian town and Qianbodian town,where the thickness is less than 10 m.In this article,through analysis of overburden layer thickness isoline distribution characteristics,there might be blind ancient river in south of the study area.