Preliminary Study On The Characteristics And Attenuation Characteristics Of Strong Earthquake In Sea Areas Based On S-net

China is geographically located between the seismic belts of the Eurasian and Pacific tectonic plates,where multiple subduction zones exist within its territorial waters.The geological conditions in this region are highly intricate,and the seismic events in the marine environment significantly influence the safety of marine engineering structures.With the rapid development of coastal economies and the sustained advancement of the maritime power strategy,there is an urgent requirement for seismic risk prevention and control measures in marine engineering structures.This paper investigated the characteristics and attenuation properties of seabed seismic motion to furnish references for the seismic design of forthcoming marine engineering structures.Seismic records from the Japanese S-net were employed to conduct a preliminary analysis of seismic motion characteristics while exploring the distinctions between the seabed and land-based seismic motion.Additionally,the study established seismic motion attenuation relationships specific to various seismic sources.The main research contents are as follows:1.The deployment status of the Japanese S-net seafloor network was introduced,and the necessity and uniqueness of data processing for the S-net network were explained.Following the procedure of "collection-screening-processing-classification-grouping",the seismic motion data from the S-net network in marine regions were processed,and land-based seismic motion data from the same seismic sources were compiled for comparative analysis of marine-land differences.2.The seismic parameters associated with marine seismic motion,including amplitude,spectrum,and energy,were analyzed,while the differences in seismic spectra between marine and terrestrial environments were compared.The results revealed that the vertical component intensity of seismic motion in marine regions exhibited a significantly lower amplitude and energy than the horizontal component.Additionally,the horizontal component of the duration parameter is notably smaller than the vertical component.Furthermore,the spectral amplification coefficient in marine regions displayed a distinct shift towards more extended periods compared to the land-based amplification coefficient spectra,indicating the presence of a more abundant long-period component,exceeding the commonly used platform value of 2.25 prescribed by current seismic design codes.3.The attenuation relationships for peak ground acceleration and acceleration response spectra of four types of seismic sources in the Japan Trench region were established.The similarities and differences in the attenuation relationships among different seismic source types were analyzed,and a comparative analysis was conducted with existing attenuation relationships for subduction zone seismic motion in marine and terrestrial domains.The results indicated that the seismic attenuation curves of unburied stations for different seismic source types exhibited varying amplification ratios compared to the buried stations.Moreover,as the period increased,the amplification ratio gradually decreased.Notably,shallow crustal earthquakes demonstrated a more pronounced reduction in the amplification ratio compared to other seismic source types.Additionally,the subduction zone earthquake model proposed in this study aligned more closely with existing seismic motion attenuation models in the Japanese marine region,while the on-land subduction zone model underestimated the seismic motion in the marine environment to a certain extent.