Relative Sea Level Variations Caused by Subduction

By means of a stratified Earth model with viscoelastic rheology, we have studied the long-term global fluctuations of Relative Sea Level (RSL) induced by subducting slabs. We have computed RSL variations for both a single subduction and a realistic distribution of slabs by a numerical simulation based on a simplified model of the subduction process. RSL is determined by the offset between the geoid and the dynamic topography; our analysis demonstrates that the latter provides the prevailing contribution. We have studied, in addition, the effects of rheological stratification upon the amplitude and time-evolution of these two quantities and, consequently, of RSL fluctuations. According to our results, an upper bound for the rate of RSL associated with subduction is of the order of 0.1 mm/yr, in agreement with previous studies. This rate of sea level variation is comparable with that attributed to changes in the tectonic regime on a large scale. This preliminary result corroborates the suggestion by other authors to include subduction in the list of geophysical mechanisms which contribute to long-term RSL fluctuations.