How the Continents Deform: The Evidence from Tectonic Geodesy
Ann. Rev. Earth Planet. Sci., 17, 237-262 (2009)
Wayne Thatcher Online Article
Non-technical summary: Space geodesy now provides quantitative maps of the surface velocity field within tectonically active regions, supplying constraints on the spatial distribution of deformation, the forces that drive it, and the brittle and ductile properties of continental lithosphere. Deformation is usefully described as relative motions among elastic blocks and is block-like because major faults are weaker than adjacent intact crust. Despite similarities continental block kinematics differs from global plate tectonics: blocks are much smaller, typically ~100-1000 km in size; departures from block rigidity are sometimes measurable; and blocks evolve over ~1-10 Ma timescales, particularly near their often geometrically irregular boundaries. Quantitatively relating deformation to the forces that drive it requires simplifying assumptions about the strength distribution in the lithosphere. If brittle/elastic crust is strongest, interactions among blocks control the deformation. If ductile lithosphere is the stronger, its flow properties determine the surface deformation and a continuum approach is preferable.
Caption for Figure: Local forces and block rotations determined by GPS velocity field analysis in 6 regions worldwide. Subduction resistance is denoted by solid circles; trench suction by straight solid arrows; sense of block rotations by curved arrows; and rotation axes by dot and semi-circular arrow.
