SCEC INSTANeT News
	Three Software Packages for Stress Triggering and Deformation Studies Available

In September 1999, SCEC held a workshop to introduce people to three software packages useful for stress triggering and deformation studies. These can be freely downloaded, along with manuals and tutorials: 1. Coulomb 1.0 (by S. Toda, R. Stein and G. King) can be downloaded from http://quake.wr.usgs.gov/study/deformation/ Coulomb is a fast, menu-driven Mac program rich in graphics. It performs 3D elastic dislocation calculations of deformation and stress in an elastic halfspace. It is optimized to explore stress transfer associated with earthquakes, fault creep, and dike inflation or deflation events. It can input fault slip and focal mechanism files, and can output displacements, optimally-oriented Coulomb stress changes and resolved stress changes at any depth on any surface in a Cartesian x,y,z coordinate system. A complete manual and set of tutorial files is included. It runs on a PowerPC Mac, preferably G3 or later. 2. 3D-DEF (by J. Gomberg & M. Ellis). An online guide is at http://www.ceri.memphis.edu/3ddef/guide.html where instructions may be found for downloading the code. 3D-DEF performs elastic dislocation boundary-element calculations, which permit one to examine, for example, how faults will slip in response to applied stresses (which may be expressed in a number of different ways), how the growth of a dike will influence enveloping stresses, how stresses are transferred from one fault to another, etc. Unlike finite element codes, little or no gridding is needed. The program enables a variety of boundary conditions to be applied, which makes the model quite flexible. 3D-DEF is a stand-alone program built around the Okada (1992) Green's functions and runs on any computer with a FORTRAN compiler. A great variety of output files are possible. 3. VISCO1D (by F. Pollitz) can be downloaded from http://www-geology.ucdavis.edu/~pollitz/ VISCO1D calculates the postseismic response of a spherically stratified elastic-viscoelastic medium to the stresses generated by fault slip or dike opening occurring in one of the elastic layers. The response is 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 flexible, allowing the determination of time-dependent postseismic deformation fields (displacement and strain) at any depth level. For more information contact: Nancy Sandoval nsandoval@isdmnl.wr.usgs.gov

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