VISCOELASTIC FLOW IN THE LOWER CRUST AFTER THE 1992 LANDERS, CALIFORNIAL EARTHQUAKE

Space geodesy showed that broad-scale postseismic deformation occurred after the 1992 Landers earthquake. Three-dimensional modeling shows t hat afterslip can only explain one horizontal component of the postsei smic deformation, whereas viscoelastic flow can explain the horizontal and near-vertical displacements. The viscosity of a weak, about 10-km -thick Layer, in the Lower crust beneath the rupture zone that control s the rebound is about 10(18) pascal seconds. The viscoelastic behavio r of the lower crust may help to explain the extensional structures ob served in the Basin and Range province and it may be used for the anal ysis of earthquake hazard.