VISCO1D - A Program Package to Calculate Quasi-Static Deformation on a Layered Spherical Earth
VISCO1D is a program package designed to describe the response of a spherically stratified elastic-viscoelastic medium to the stresses generated by an earthquake occurring in one of the elastic layers. The response is described in a spherical earth geometry in terms of a spherical harmonic expansion of spheroidal and toroidal motion components, each component representing one "mode" of relaxation with its own characteristic decay time and spatial deformation pattern. It is highly flexible and allows the determination of time-dependent postseismic deformation fields (three components of displacement and six independent components of strain) at any depth level. It handles shear dislocations on a specified fault plane, or extension across a specified fault plane. Use of the program package consists of four main parts:|
1. Specification of a stratified Earth model (elastic moduli and viscosity of every layer).
2. Identification of spheroidal and toroidal motion modes on this Earth model, consisting of a set of characteristic decay times for each spherical harmonic degree.
3. Determination of the corresponding displacement-stress vectors for each of these modes.
4. Determination of postseismic deformation at specified times, observation points (lat,lon,depth), and source geometry and slip.
There are two sets of programs, one designed for non-gravitational viscoelastic response and the other for gravitational viscoelastic response. The former runs considerably faster.
[Summary provided by the USGS.]
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