Geophysical Finite-Element Simulation Tool (GeoFEST): Algorithms and Validation for Quasistatic Regional Faulted Crust Proble J AY PARKER,GREGORY L YZENGA,CHARLES NORTON ,CINZIA ZUFFADA, MARGARET GLASSCOE ,J OHN L OU, and A NDREA DONNELLAN Abstract—GeoFEST (Geophysical Finite Element Simulation Tool) is a two- and three-dimensional finite element software package for the modeling of solid stress and strain in geophysical and other continuum applications. It is one of the featured high-performance applications of the NASA QuakeSim project. The pr is targeted to be compiled and run on UNIX systems, and is running on diverse systems including sequent message-passing parallel systems. Solution to the elliptical partialdifferential equations is obtained by finite element basis sampling, resulting in a sparse linear system primarily solved by conjugate gradient iteratio tolerance level; on sequential systems a Crout factorization for the direct inversion of the linear system is supported. The physics models supported include isotropic linear elasticity and both Newtonian and powe viscoelasticity, via implicitquasi-static time stepping. In addition to triangular, quadrilateral, tetrahedral and hexahedral continuum elements, GeoFEST supports split-node faulting, body forces, and surface tractions software and related mesh refinement strategies have been validated on a variety of test cases with rigorous comparison to analytical solutions. These include a box-shaped domain with imposed motion on one surfa of strike slip faults in stepover arrangement, and two community-agreed benchmark cases: a strike slip fa enclosing box, and a quarter-domain circular fault problem. Scientific applications of the code include the modeling of static and transient co- and post-seismic earth deformation, Earth response to glacial, atmosp hydrological loading, and other scenarios involving the bulk deformation of geologic media. 1. Introduction In order to simulate viscoelastic stress and flow in a realistic model of the Earth’s crustand uppermantle,themodeling technique mustbe ableto accommodate a complicated structure consisting of material layers and blocks, with imbedded faults which may cut at arbitrary angles. Stress and displacement features will vary most r near the faults and particularly near fault-terminations. These features argue for fully three-dimensional finite-element modelingin the time domain.Two-dimensional modeling, semi-analytical techniques, finite-difference and semi-spectral methods eith cannot model significant features or geometry of interest, or require gross oversamp in regions of little interest, leading to impossible computational requirements. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, U.S.A. E-mail: Jay.W.Parker@jpl.nasa.gov Pure appl. geophys. 165 (2008) 497–521 Birkha¨user Verlag, Basel,2008 0033–4553/08/030497–25 DOI 10.1007/s00024-008-0325-9 Pure and Applied Geophysics