Comparative Study Of Intensity Envelope Of Acceleration Records Between Underground Bedrock And Surface

The envelope parameter of ground motion intensity is one of the necessary and important parameters for human site vibration synthesis,and it is a very important part in the seismic safety evaluation of engineering site.Due to the lack of natural seismic records,synthetic ground motion is an important source of seismic response input in soil layer and time history of ground motion on the surface.In general,ground motion envelope parameters of bedrock sites can be obtained through the ground motion attenuation relationship.Most of the existing research results are the ground motion attenuation relationship of bedrock sites,and there are few ground motion attenuation relations of soil sites,which leads to the failure to obtain reasonable intensity envelope parameters for determining the time history of ground motion.In order to solve this problem,the intensity envelope parameters of the strong seismic records of downhole bedrock and the corresponding surface strong seismic records in the same borehole under each seismic event are obtained by using the selected strong seismic data of KiK-net station,and the difference of the intensity envelope of downhole bedrock and surface ground motion time history is studied,as well as the relationship between this difference and site information.The research results can provide reference for the parameters of composite intensity envelope of ground motion in soil layer sites based on the results of bedrock.The main work of this paper is as follows:1.This paper briefly reviews the research history and existing achievements of intensity envelope function parameters,and on this basis,expounds the significance and feasibility of the comparative study of time-history envelope function parameters of underground bedrock and surface ground motion.2.The information of KiK-net strong earthquake station in Japan is collected,and its sites are classified by using the Chinese method.The research station and its typical underground bedrock and surface ground motion records are selected,and the advantages of obtaining the ground motion intensity envelope function by combining two vertical horizontal ground motion records are demonstrated.3.Through comparative analysis,the existing problems in the research results of the parameters of the strength envelope function are pointed out,and a modification method is proposed to solve the above problems,forming a mutual parametric method to determine the parameters of the envelope,and is determined as the research method of this paper.4.The ground motion records of the research station’s surface and underground bedrock were classified according to the category of the site,and their envelope function parameters and variation rules were calculated respectively.By comparing the change rate of the surface relative to the parameter value of the underground bedrock envelope,a more reasonable general formula was summarized for the class Ⅱ site,and the results showed:(1)t1 and ts as a whole show a spatial plane distribution across the M-axis,and can be represented by M and R separately,and R has a higher priority than M;(2)C as a whole presents a spatial surface distribution,which can be approximated by M and R separately,and M has a higher priority than R;(3)For the data scatter selected by the specified conditions in this paper,there is an obvious rule between magnitude M and the maximum propagation distance R.(4)The difference values of t1 and ts on the surface and underground bedrock oscillate up and down around the zero line.With the increase of the epicenter distance,this difference value rises as a whole.With the increase of the magnitude of the earthquake,the phenomenon of the difference of beam absorption tends to be smooth,and the oscillation range is smaller.(5)The difference between surface and underground bedrock of parameter C rises steadily with the increase of earthquake magnitude.For type Ⅲ sites:(1)the difference between surface t1 and ts and underground bedrock is mostly positive,that is,the surface t1 and ts values are generally larger than underground,but the shock range is greatly different;(2)The difference between the surface of C and the underground bedrock is mostly negative,that is,the C value of the surface is generally smaller than that of the underground rock,and the attenuation is slower.