Quasi-static strains and tilts due to faulting in a layered half-space with an intervenient viscoelastic layer.

Abstract

Quasi-static strains and tilts on the surface are investigated for a dislocation source in a stratified elastic half-space with an intervenient, Maxwellian viscoelastic layer. Integral representations for the strains and tilts are obtained by differentiating those for the displacements derived in a previous paper (MATSU'URA et al., 1981) with respect to space coordinates. Evaluation of the integral is carried out by using a method of approximating a part of the integrand by a simple analytical function.Numerical examples of the strain and tilt fields are computed for some typical cases to examine general features of the viscoelastic surface deformations. Time-dependent behavior of the tilt fields caused by a point dislocation source in the elastic surface layer of a three-layered model is examined for various cases with different thicknesses of the viscoelastic layer. A common feature to all the layered structure models is that the amount of the viscoelastic deformation increases gradually with time, and the deformed area extends out quite slowly from the source. The change in the thickness of the viscoelastic layer affects the amount and extent of the deformation. Patterns of the shear strain, principal strain, and the ground tilt due to a finite-dimensional fault are presented for a three-layered model (Model III), and compared with those for different types of structure models, such as a viscoelastic half-space model (Model I) and a two-layered model composed of an elastic surface layer overlying a viscoelastic half-space (Model II). Patterns of the viscoelastic deformation fields for Model I are quite different from those for the layered structure models. The difference between Model II and Model III is not so distinct, except that the deformation field for Model III is somewhat restrained in amplitude and extent, compared with that for Model II.