Thermoelastic and poroelastic deformation of the solid Earth driven surface temperature and groundwater level variations

Variations in surface temperature and groundwater pressure within aquifer systems generate internal thermoelastic and poroelastic strain in the shallow subsurface, producing surface deformation and crustal stress perturbations. We develop a general mathematical framework to compute surface displacements and stresses at depth driven by internal strain, accounting for realistic mechanical properties of the Earth, including depth-dependent layering and lateral heterogeneities. 
We show that variations in surface temperature induce deformation below layers affected by internal strain and surface horizontal displacements that scale with the Young’s modulus of the shallow layers where internal strain occurs. Because these layers generally have weak elastic moduli across continental regions (soils, weathered rock, etc.), long-wavelength thermoelastic horizontal deformation is predicted to be negligible. In contrast, vertical displacements driven by thermal expansion within shallow weak layers are expected to reach the millimeter level, implying that thermoelastic effects should be considered when interpreting GNSS signals, in particular at the annual timescale.
At regional scale, lateral contrasts in elastic properties, such as transitions from bedrock to sedimentary basins or across fault damage zones, can produce annual thermoelastic horizontal displacements up to a few mm. The associated annual thermoelastic stress perturbations at depths of a few km may reach several kPa, locally exceeding stresses induced by seasonal hydrological loading, suggesting a potential contribution of surface temperature forcing observed seasonal modulation of seismicity. Over longer timescales, progressive climate-driven warming may also cause non-negligible stress perturbations in intraplate regions. 
Using the same formalism, we investigate deformation and stresses induced by poroelastic pressure variations in aquifer systems. We show that for 10 m variations of the water table, vertical displacements of a few mm to a few cm are expected and lateral variations of elastic properties can generate horizontal deformation of a few mm and crustal stress perturbations of several kPa.