Study On Prediction Model And Calibration Of Design Response Spectrum Of Offshore Ground Motions In Japan Subduction Zone

With the development of global marine resources,more and more attention has been paid to seismic fortification in ocean engineering,but the research on marine seismic engineering is very limited at present.The South Sea and the Bohai Sea in China are located in seismic zones with strong activity and frequent earthquakes,so seismic fortification and seismic zoning for offshore regions are particularly important.The seismic design of offshore structures such as cross-sea Bridges,undersea tunnels and offshore oil platforms requires offshore ground motion as input,so the study of offshore ground motion characteristics can provide a reference for the zoning and seismic fortification of offshore areas.This paper collected more than 6000 offshore ground motion records from three seafloor observation networks in Japan,proposed the offshore ground motion prediction models,and analyzed the characteristic parameters of the design spectra of offshore regions.The main research work of this paper includes the following four aspects:(1)Based on the offshore ground motion database of different source types,the prediction models of offshore ground motion for subduction slab earthquake,interface earthquake,shallow crustal and upper mantle earthquakes in Japan are established by regression analysis and parameter smoothing.The uncertainty of the prediction models is analyzed,and the single standard deviation of different models is presented.(2)To analyze the differences between offshore and onshore ground motion prediction models,the existing onshore model and the three offshore GMMs established in this paper were used to analyze and compare the differences between offshore and onshore models from the source term,path term and site term,to reveal the differences in the attenuation characteristics and the differences in the response spectrum in the long period under the complex geological environment of the seafloor.(3)To investigate the differences between the three established prediction models under different earthquake types,the coefficients and amplitudes of the three established models in this paper were compared to reveal the differences among the prediction models of the subduction interface,subduction slab,shallow crust and upper mantle earthquakes of the subduction zone,and the uncertainties among the different models were also compared.The comparison results show that it is reasonable to establish the three offshore prediction models according to the seismic types.(4)Different types of response spectra were selected to investigate the applicability and stability of various improved differential evolution algorithms in calibrating the response spectrum.The analysis results show that compared with the standard DE algorithm,the GLDE algorithm can achieve stable and accurate calibration of all types of ground motion,so it is recommended to use the GLDE algorithm to calibrate the design response spectrum.According to the seismic source types,magnitude,distance and site conditions,the characteristic parameters of the design response spectrum of offshore ground motions under different site conditions and different source types are presented by GLDE algorithm.Meanwhile,the comparison with the seismic code of onshore regions shows that the design spectra of offshore and onshore ground motions have considerable differences in the platform value and long-period values.