Empirical Correlation Research Of Intensity Measures For Offshore Ground Motions Of Japan’s ETMC System

Selecting suitable input ground motions for offshore engineering is a crucial problem and important challenge in the field of offshore seismic engineering.The empirical correlation model is developed to predict the correlation between two ground motion parameters.It can be used not only for the selection of ground motion records based on generalized conditional intensity measures(GCIM),but also for probabilistic seismic hazard analysis based on vector intensity measures(VPSHA).Previous studies of empirical correlation models are mainly based on onshore ground motions,and there are no studies on offshore ground motions.Based on 892 offshore ground motion records and 4033 onshore ground motion records of ETMC system in Japan,this paper studied the empirical correlation between offshore ground motion spectral parameters(response spectrum and elastic input energy spectrum)and four categories of intensity measures(IMs).The main work is as follows:1.To fully consider the characteristics of ground motions,the 10 IMs are divided into four categories:(1)amplitude:peak acceleration(PGA),peak velocity(PGV),peak displacement(PGD);(2)duration:significant duration(DS5-95,DS5-75);(3)frequencycontent:mean period(Tm),smoothed spectral predominant period(To),average spectral period(Tavg);(4)cumulative effect:cumulative absolute velocity(CAV),Arias intensity(IA).The offshore ground motion prediction equations(GMPEs)of the above IMs were established,and the rationality of the GMPEs were verified by residual analysis and test of normality.2.The rationality of the GMPEs of the offshore ground motion response spectra in 0.1～10.0 s was verified.Based on the GMPEs,the empirical correlation between the offshore ground motion response spectra and the four categories of IMs were analyzed by fish-z transformation considering the limited numbers of samples.To compare the empirical correlation between the offshore and onshore ground motion response spectra and the above IMs,this paper calculated the empirical correlation between the onshore ground motion response spectra and the above IMs with the same source of earthquake and similar hypocentral distance,and compared the differences between offshore and onshore ground motions.3.Based on the GMPEs,the empirical correlation between the equivalent velocity of relative and absolute input energy(VEr,VEa)of offshore ground motions and four categories of IMs were analyzed by fish-z transformation considering the limited numbers of samples.The empirical correlation of VEr and VEa with the above IMs of onshore ground motion were calculated for the same source of earthquake with similar hypocentral distance,and the differences of offshore and onshore ground motions were compared.4.To facilitate the application of empirical correlation conclusions in VPSHA and ground motion records selection based on the method of GCIM.According to the results of the empirical correlation between the spectral parameters and the four categories of IMs,the correlation coefficients are interpolated,and the parametric prediction equations of empirical correlation of the spectral parameters with the four categories of IMs were given by the least square method.It is a piecewise continuous function of the period T of single-degree of freedom system.The models are not only beneficial to the application of empirical correlation,but also can study the periodic points other than the periods studied in this paper.