Discussion On The Influence Factors Of Kappa In Northeastern Japan

In the 1980 s,seismologists found that as frequency beyond a specific value,the acceleration Fourier amplitude spectrum has obvious decrease,the research on the phenomenon of the high frequency attenuation is not intermittent.In recent years,in the engineering seismology field,the establishment of attenuation relationship in the absence of strong motion records area,along with the numerical simulation method,the high frequency attenuation factor kappa(?)research is increasing,especially after the NGA-East project,the heat of the study predominate continue to increase.This paper chooses the northeast area of Japan(36°N-40°N,138°E-143°E)as a target area,which is rich in seismic records.Using the broadband digital seismic network F-net observed 91 small earthquakes(MW=3.5-4.5,focal depth?30km,hypocentral distance?300km)from January 1,2000 to June 1,2003 of the 2094 records and 14 large earthquakes(MW=4.5-5.8,focal depth?30km,hypocentral distance?300km)of the 321 records,while supplementing the strong earthquake networks KiK-net observed 551 earthquakes downhole records(Mw=3.5-4.5,focal depth?30km,hypocentral distance?300km)from January 1,2011 to January 1,2014.Combined with the characteristics of these data,using the method of Anderson and Humphrey,simultaneous broad-band spectral fit method,fixed the stress drop method and classic acceleration spectrum method to calculate ? value,the first three are broadband inversion method,the latter is a limited bandwidth method.As a whole,the results of the three broadband inversion are closer,and the ? value of the finite bandwidth method is higher than the previous three ? values.The theoretical foundation and influencing factors of ? have been a hotspot of discussion.For ?'s influencing factors predominate the discussion,the common view is site condition plays a main role,and the influence degree of the source and the transmission route is different depending on the research area.In this article seismic record ? values and the hypocentral distance linear regression toward the source and the station to obtain the ?0 and ?s,aiming at the problem of insufficient of strong motion records in some regions,research the difference between KiK-net stations recorded ?0 and F-net stations recorded the ?0 in the same area,discuss the possibility of using seismic observation network data to determine regional ?0 value.The results show that the ?0 of seismic observation network F-net stations is mostly higher than strong-motion network KiK-net downhole stations ?0,the difference ??0 mostly in the range of-0.01 s to 0.025 s.As a result of the two kinds of seismic network stations placed in different site conditions,the existence difference can be explained the relationship between shear wave velocity,illustrates that in the process of establishing ground motion attenuation based on seismography,the feasibility of determining the ?0 value with the help of seismic observation network data,also explains the rationality of using ?0 as a parameter when adjusting the ground motion attenuation relationship of hard rock to engineering rock sites.In order to answer the problem of whether the ? of small and medium magnitude earthquake can be applied to greater ground motion estimation.This article will magnitude and the ?s of the large earthquakes(MW?4.5)and the small earthquakes(MW=3.5-4.5)recorded by F-net and KiK-net are linearly regressed,the goodness-of-fit of corresponding methods are low,and the linear relationship with the magnitude is not obvious.It illustrate that the methods used to eliminate the effects of the source are effective.The results of two types of data in the simultaneous broad-band spectral fit method are not very different.Considering that the classical acceleration spectrum method directly measures ? value in the high frequency part of acceleration Fourier amplitude spectrum,which includes the influence of the source,propagation path and site,it is proposed to decouple the influencing factors of ? in F-net and KiK-net surface,the downhole observation spectrum to remove the source spectrum,inelastic attenuation and site amplification to obtain ?0,the ?0 into the formula for calculation of Fourier amplitude spectrum and ?0-AS into the results together with the compared with the actual spectrum,the slope of the improved spectrum amplitude in the high frequency part is consistent with the real spectrum,which is more reasonable.