Transient deformations: understanding Earth's interior through climate change

Transient effects in the response of the Earth to surface unloading are still a matter of debate in the geophysical community. Recognizing their presence in the context of Glacial Isostatic Adjustment would represent a significant step towards a comprehensive understanding of mantle relaxation mechanisms at intermediate time scales. This Thesis explores the Andrade rheology, a transient model that has gained much success in planetary sciences. In this regard, two of the main results are the recovery of the analytical expressions of the relaxation modulus in the time domain of the Andrade model and the Love numbers for a homogeneous Andrade planet. Then, I examine the response of several Earth models including layers with Andrade rheology to different types of (glaciers) unloading. The aim is outlining the most favorable conditions under which transient deformations following an unloading event can be observed through geodetic techniques. My findings indicate that rapid changes in the load history and the position of the observation point with respect to the melting masses are parameters of utmost relevance. A shallow elastic lithosphere enables transient features to emerge more clearly, and the displacement rates reach the maximum difference from their non-transient counterparts in the regions right beneath the shrinking load, suggesting that, in the future, sub-glacial geodesy may improve the identification of transient features in the Earth’s response. Finally, even for medium-scale glaciers, the viscoelastic contributions to displacement may be significant already over short time periods (<15 yr). These kinds of studies become even more crucial in the context of present-day climate change. Hence, the growth both in number and magnitude of phenomena like extreme melting events and calvings, may increase our possibility to observe transient signals in the Earth’s response.