POSTSEISMIC DEFORMATION AND STRESS DIFFUSION DUE TO VISCOELASTICITY AND COMMENTS ON THE MODIFIED ELSASSER MODEL

Finite element techniques have been used to investigate the far-field deformation and stress changes due to asthenospheric viscoelastic relaxation following a dip-slip earthquake. The diffusion of extensional stress toward the subduction zone following a thrust earthquake on land is qualitatively consistent with the modified Elsasser model as proposed by Rydelek and Sacks (1988, 1990) to explain the coupled occurrence of land and sea earthquakes near Japan. However, the magnitude of the diffusing tensional signal is significantly smaller. The nominal model consists of a partially faulted elastic lithosphere overlying a viscoelastic substrate. Other models consider thin channel flow, rupturing of the entire elastic lithosphere, and changes in the depth of faulting. While some of these changes have significant impact on the magnitude and spatial features of the stress and deformation field, the far-field stress remains small. Numerical experiments demonstrate that the assumptions of the modified Elsasser model accentuate uniaxial deformation. When these assumptions are replicated in the finite element calculations, reasonable agreement between the models is achieved.