Separating Surface Loading Deformation from Time-dependent Tectonic Deformation

Southern Alaska features both large amplitude surface loading signals and large tectonic signals. Secular surface mass variations are caused mainly by the melting of glacier ice, which is concentrated in the coastal mountains. Seasonal surface mass variations are caused mainly be snow accumulation and melt, and thus have a long wavelength component in addition to a concentration in the coastal mountains. Interannual variations in temperature and snowfall further complicate the picture. In some places, the tectonic deformation is also time dependent due to slow or transient slip events, and postseismic deformation. To first order, much of the seasonal deformation can be removed using surface load models based on GRACE observations of gravity change, although there can be differences depending on whether seasonal average or time series mass loading deformation is removed. In addition, in some places the GRACE signal is smoothed over too large an area to provide a fully accurate correction for GPS position time series. Spatial location and wavelength of deformation, as well as temporal character, can also provide further information to separate the surface loading and tectonic deformation.