Item

Abstract

Separating multiple sources of deformation can be difficult on oceanic islands, and very long-wavelength global signals may be present. Noth Glacial Isostatic Adjustment (GIA) and the effects of present-day mass redistribution produce global deformation patterns. In the Pacific that are remote from the past and current glacier load changes, the combined signal from GIA and present-day mass redistribution predicts subsidence rates that approaches 1 mm/yr. Accurately accounting for small long-wavelength signals can be important in discriminating between alternate models of local deformation. In Hawaii, all GPS sites far from the currently active volcanoes show an additional subsidence signal likely caused either by ongoing flexural loading under the growing volcanic load, or dynamics of the deep magma system. In Iceland, ongoing glacier mass loss and glacial isostatic adjustment produce large signals, also time-dependent. In this study, we analyze continuous GPS data to assess horizontal and vertical motions. We use a variety of GIA models for which the predicted 3D velocities are available, and also recent present-day mass loading models. For the Pacific, the subsidence predicted by the sum of present-day mass loading and GIA predicts a regional subsidence signal similar to that we observe. The displacements due to present-day mass loading are time-dependent and have an overall trend. At present, the year to year variations appear to be lower than the noise level for Pacific island sites, but not for locations closer to the changing glacial loads such as the North Atlantic.