San Juan Province lies in an area where the South American Plate is affected by flat-slab subduction of the underlying Nazca Plate, the so-called Pampean flat-slab. The very shallow angle leads to a much greater degree of coupling between the subducting and overriding plates.
San Juan Province lies in a region where the South American Plate undergoes flat-slab subduction of the underlying Nazca Plate, resulting in significant coupling between the plates.