From decades to epochs: Spanning the gap between geodesy and structural geology of active mountain belts

Geodetic data from the Global Navigation Satellite System (GNSS), and from satellite interferometric radar (InSAR) are revolutionizing how we look at instantaneous tectonic deformation, but the significance for long-term finite strain in orogenic belts is less clear. We review two different ways of analyzing geodetic data: velocity gradient fields from which one can extract strain, dilatation, and rotation rate, and elastic block modeling, which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi-rigid blocks. These methods are complementary: velocity gradients are purely kinematic and yield information about regional deformation; the calculation does not take into account either faults or rigid blocks but, where GNSS data are dense enough, active fault zones and stable blocks emerge naturally in the solution. Block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults. Future technological advances should overcome many of today's uncertainties and provide rich new data to mine by providing denser, more uniform, and temporally continuous observations.