A combined ice-water reflection coefficient is developed to measure the effect of saltwater and floating ice on seabed ground motions to explore the effect of floating ice on seafloor ground motions. The combined reflection coefficient is made up of three parts: the reflection coefficient of the seawater layer, the transmission coefficient of the water layer, and the reflection coefficient of the ice layer. The combined reflection coefficient analyzes the reflection, transmission, and refraction pathways of seismic waves from the soil layer to the water layer, then to the ice layer and air, and then reflects the attenuation principle of seismic waves in an ice-water layer based on the mechanical parameters of the soil layer, water layer, ice layer, and air. The spatial coherence effect, traveling wave effect, and local site effect are then addressed using the trigonometric series method, and the ice-water layer combined reflection coefficient is utilized to analyze the influence of offshore complex sites on seafloor spatial ground motion. Under the floating ice and seawater layer, an artificial synthetic approach of multidimensional multipoint spatial ground motion is described. The random ice load time history was artificially produced using the ice load spectrum theory and the recorded sea ice parameters. The random response of a long-span cable-stayed bridge is investigated under the combined action of seafloor spatial ground motion and random ice load, and the structural responses of the bridge and tower vary substantially under the combined action of ground motion and ice load.
