Effect of submarine permafrost degradation on the vertical ground motions and vertical response spectrum of a single-degree-of-freedom system in polar ocean

Abstract

Owing to global warming, the rise in sea temperature is causing degradation of submarine permafrost, which has an impact on the seismic responses of submarine strata. Based on the revised dynamics of nearly saturated frozen porous media, a simplified model of the vertical seismic responses of submarine permafrost is established considering the degradation of its upper layer, and an analytical solution is obtained using the Laplace transform method. The governing equation of a single-degree-of-freedom system on the seafloor is further proposed, and the vertical response spectrum is obtained using the numerical inverse transformation method. The numerical results show that the vertical ground motions of the seafloor agree well with those of saturated and nearly saturated soil layers with a free surface on land and under deep-water conditions. Parametric studies show that saturation strongly affects the vertical ground motions of the seafloor, and this effect is closely related to the water depth ratio. In addition, the structural stratum parameters, including the active layer thickness ratio, permafrost thickness, and temperature, have significant effects on the vertical ground motions of the seafloor and the vertical response spectrum of the submarine lumped parameter system. Therefore, attention should be paid to the impact of submarine permafrost degradation on the vertical seismic responses of oil and gas exploitation systems in polar oceans.