Nusselt number for convection driven by tidal and radiogenic heating

The ‘traditional’ formulas giving the Nusselt number Nu as a function of Rayleigh number Ra cannot be used for low and moderate values of Ra. Moreover, the recent progress in 3D numerical modeling makes possible to determine the Nusselt number Nu as a function of Rayleigh number Ra for convection driven by radiogenic and tidal heating. We found that for low and moderate Ra: Nu(Ra) = ε(Ra+ξ)^λ where λ depends on rheology and boundary conditions, ε depends only on the mode of heating, and ξ = ε^−1/λ · Nu(Ra) makes possible to develop a parameterized theory of convection in medium size icy satellites. We also indicate some differences between convection driven by tidal and radiogenic heating and convection driven exclusively by radiogenic heating.     

Present-day deformation in São Jorge Island,Azores, from episodic GPS measurements (2001–2011)

A network of geodetic markers for high-precision Global Positioning System (GPS) surveying was established in 2001 in the island of São Jorge, at the Azores triple junction, where the North America–Eurasia–Nubia plates meet. The aim was to monitor tectonic, volcanic, and landslide-induced surface deformation in an active tectono-volcanic region. The network consisted of 17 stations, and was occupied in 2001, 2004, and 2010. GPS observations from the three episodic campaigns were analyzed using the latest geophysical models and geodetic procedures to generate a velocity field for São Jorge Island.