Anelastic Response of the Earth’s Crust Underneath the Canary Islands Revealed from GPS Vertical Displacements and Gravity Ocean Tide Loading

Abstract

We report on the analysis of M2 kinematic GPS vertical displacement and tidal gravity measurements using 26 GPS and 3 gravimetric stations across the Canarian archipelago. In this region, recent ocean tide models have standard deviations of differences lower than 1.0 cm in amplitude and 2.9 degrees in phase, and are in close agreement with tide gauges (FES2014b shows an average difference of 1.9 cm and 1.9 degrees in amplitude and phase lag, respectively). These small ocean tide errors allow us to use the residual differences between observed and predicted ocean tide loading (OTL) values to study the elastic and anelastic properties of the solid Earth around the Canaries. First, in the prediction of OTL, we replaced the standard PREM earth model with STW105 and then S362ANI, which reduced the misfit between observations and predicted OTL values (from 1.1 to 0.6 mm for vertical displacements and 0.3 to 0.1 µGal for gravity with both models). Next, these models were adjusted for tidal periods by considering a constant quality factor Q at frequencies ranging from 1 s to 12.54 hours, which represent the absorption band of the asthenosphere. This yielded residual differences between observed GPS M2 vertical displacement and modelled values of less than 0.5 mm, except for the easternmost islands of Lanzarote and Fuerteventura, where they reach up to 2 mm at some stations. It is hypothesised that mantle upwelling underneath the Canary Islands, creating spatial variations in the elastic properties, causes the large residuals observed in the eastern islands.