The space geodesy revolution for plate tectonics and earthquake studies

Abstract

Even if plate tectonics was a truly significant unifying theory that began to give sense to a series of different geological observations, plate motions were considered scattered. The advent of space geodesy confirmed and greatly refined the models of plate kinematics, allowing also to study the motion of the lithosphere with respect to the inner layers of the Earth. Switching from the no net rotation to the hotspot reference frames, plate motion assumes coherence with a mean global westward drift of the lithosphere with respect to the mantle. However, the driving forces of plate tectonics are still under investigation and space geodesy may provide fundamental tools to develop comprehensive models which can take into account the contributes of mantle density gradients and astronomical forces, as Earth’s rotation and tides. This paper is dedicated to Prof. Michele Caputo who was a pioneer in measuring the misalignment of the tidal bulge with respect to the Earth–Moon gravitational alignment. The misplaced mass in excess may account for the westerly directed torque of the lithosphere relative to the mantle. Local GPS networks and satellite observations are providing new insights on plate boundary tectonics and allow unravelling the evolution of the interplay between the shallow brittle upper crust and the underlying visco-plasticlower crust, which is deforming in a steady state regime without releasing relevant seismic waves. Along active tectonic areas, zones marked by low strain rates are suitable to store larger energy, subsequently dissipated during the coseismic stage. GPS and InSAR observations have widely increased the capability to monitor the spatial and temporal variations of deformation. The coseismic deformation pattern suggests a different mechanism of energy store and release, mainly gravitational in extensional tectonic settings and essentially elastic in strike-slip and contractional tectonic settings. The increasing details provided by future dense and low-cost geodetic networks will allow to detect reliable deformation transients and new insight on seismic precursors.