Relationship Of Seafloor And Sea Water Motion And Its Application In Tsunami Generation By Considering Water Comporessibility

Traditional tsunami research assumes that seawater is incompressible,but more and more observations and records indicate that water compressibility may play an important role in tsunami generation and propagation.Particularly,sound waves in the water are excited during the tsunami generation process,and whether they can be used for tsunami warning attracts many researchers' attention.However,the theory of tsunami generation with water compressibility taken into account has not been fully developed.In addition,tsunamis are generated by earthquakes,which radiate seismic waves that may contaminate the sound waves in the water for tsunami warning purposes.In this study,we perform a preliminary study of the tsunami generation process in both theoretical and numerical means.Considering water compressibility,we first derive the theoretical solution of the relationship between seafloor motion and seawater motion,and check the theoretical solution using the finite-element software ADINA,and realistic seismic and tsunami records.We find that the numerical results obtained from ADINA are consistent with the theoretical solution,but the application to realistic seismic and tsunami records is not satisfactory.At low frequencies,the results of the theoretical solutions are consistent with the records.However,at high frequencies,there are still phase lags and amplitude differences between the theoretical results and the records.The reason might be associated with the low sampling rate of the records and possible gain errors of the sensors.Next,we study the relationship between the permanent deformation of the seafloor and the change of the sea surface elevation of compressible seawater.We us ADINA and demonstrate that the classic relationship between the permanent deformation of the seafloor and the change of the sea surface elevation of incompressible seawater is still valid by accounting for water compressibility.It is pointed out that at the initial stage of the earthquake,the sea surface elevation of compressible seawater is affected by seismic waves and sound waves.Finally,we discuss the acoustic waves induced by the permanent deformation of the seafloor.We find that the sound waves travel more slowly than the seismic waves,and cause differences in the energy spectrum of the oceanbottom pressure records.Thus,the ocean-bottom pressure records may be used for tsunami warning by investigating its components of water sound.