Finite element modeling of stress in the nazca plate: Driving forces and plate boundary earthquakes

Finite element methods are applied to an analysis of the state of stress within the Nazca plate due to plate driving forces and large plate boundary earthquakes. The wave front solution technique is used in a static analysis of the deformation of an elastic plate. Ridge pushing forces are required in all models that match the nearly east-west horizontal compression inferred from two thrust earthquakes in the interior of the Nazca plate. The net pulling force of the subducting slab on the oceanic plate is at most comparable to ridge pushing forces. Regional intraplate deviatoric stresses are estimated to be on the order of a few hundred bars. Changes in the Nazca intraplate stress field due to the 1960 Chilean earthquake are, at most, a few tens of bars locally and about one bar at greater distances into the plate. Such variations only occur after complete stress relaxation of a viscous asthenosphere and imply that the changes in the intraplate stress field due to large plate boundary earthquakes are probably not significant unless the lithosphere is very near failure. Displacements within the plate due to large plate boundary earthquakes should be observable using precise geodetic measurement techniques.