MODEL FOR THE EARTHQUAKE CYCLE IN UNDERTHRUST ZONES

The time-dependent surface deformation due to thrust faulting in an elastic plate overlying a viscoelastic half space is examined and compared with geodetic measurements of earthquake-related crustal movements from Japan. The model fault is two-dimensional, and the half-space rheology is that of a Maxwell solid whose instantaneous response to applied loads is purely elastic but which subsequently flows to relieve imposed shear stresses. A characteristic feature of shallow-angle underthrusting shown by these computations is that buried slip produces predominantly land uplift, while asthenospheric relaxation due to surface faulting results principally in surface downwarping. These distinctive patterns, also reflecte din the measured deformation, are particularly useful in formulating a viable model for the entire earthquake cycle. For the model constructed in this way, coseismic faulting in the upper part of the plate transfers a load to the lower lithosphere and asthenosphere, inducing post-seismic slip downdip of the seismic rupture and relaxation in the asthenosphere, these transients eventually merging into the steady buried slip and smoother asthenospheric flow that characterize the interseismic phase of the deformation cycle.- Authors