3D-Def: a set of Fortran programs written by Joan Gomberg (USGS) and Mike Ellis (British Geological Survey) allows the user to make a three-dimensional boundary-element model for calculation of stresses, strains, and displacements within and on the surface of an elastic half-space; there is no bottom to the model. The power of the model comes from the ability to a) solve for a variety of deformation quantities on a variety of faults and planes simultaneously, and b) to drive the deformation in relatively realistic (and therefore potentially complex) ways.
DEFNODE: a Fortran program written by Rob McCaffrey to model elastic lithospheric block rotations and strain rates, and locking or coseismic slip on block-bounding faults. Block motions are specified by spherical Earth angular velocities (Euler rotation poles) and interseismic backslip is applied along faults that separate blocks, using an elastic halfspace. The faults are specified by lon-lat-depth coordinates of nodes (forming an irregular grid of points) along the fault planes. The parameters are estimated by simulated annealing or grid search. Various types of data can be used, including GPS velocities, fault slip rates, earthquake slip vectors, geodetic strain rates, etc.
Blocks and dislocations: Present-day deformation at plate boundaries, as recorded by GPS velocities and InSAR measurements, integrates both plate motions and earthquake cycle processes. Constraining the magnitudes of these effects provides constraints on the nature of slip partitioning at plate boundaries and rates of elastic strain accumulation in the seismogenic upper crust. The Blocks suite of Matlab codes (including a "point-and-click" interface for model building) was developed at Harvard University and the Massachusetts Institute of Technology by Brendan J. Meade, John. P. Loveless and Bradford H. Hager (see Meade and Hager  and Meade and Loveless ). Parameters (rotation vectors, slip rates, spatially variable fault coupling, internal block strain rates) are estimated linearly enabling both formal uncertainty propagation and classical resolution analysis.
Coulomb 3.2, by Shinji Toda (DPRI/Kyoto Univ.), Ross Stein & Volkan Sevilgen (USGS, Menlo Park), and Jian Lin (WHOI), is intended both for publication-directed research and for college and graduate school classroom instruction. The authors believe that one learns best when one can see the most and can explore alternatives quickly. So the principal feature of Coulomb is ease of input, rapid interactive modification, and intuitive visualization of the results. The program has menus and check-items, and dialogue boxes to ease operation. The internal graphics are suitable for publication, and can be easily imported into Illustrator, GMT, Google Earth, or Flash for further enhancements. Coulomb is a MATLAB application and so runs on all computers. The software, tutorial files, and a 56-pg full-color user guide can be freely downloaded.
Coulomb is designed to let one calculate static displacements, strains, and stresses at any depth caused by fault slip, magmatic intrusion or dike expansion/contraction. One can calculate static displacements (on a surface or at GPS stations), strains, and stresses caused by fault slip, magmatic intrusion or dike expansion. Problems such as how an earthquake promotes or inhibits failure on nearby faults, or how fault slip or dike expansion will compress a nearby magma chamber, are germane to Coulomb. Geologic deformation associated with strike-slip faults, normal faults, or fault-bend folds is also a useful application. Calculations are made in an elastic halfspace with uniform isotropic elastic properties following Okada . Processes not included in Coulomb are also important, such as dynamic stresses, pore fluid diffusion, and viscoelastic rebound. Further, basins and crustal layering modify the stresses in comparison to the elastic halfspace implemented in Coulomb. Nevertheless, we believe that a simple tool that permits exploration of a key component of earthquake interaction has great value for understanding and discovery.
VISCO1D, a set of Fortran programs written by Fred Pollitz, calculates 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.
Meade, B. J. and B. H. Hager, Block models of crustal motion in southern California
constrained by GPS measurements, J. Geophys. Res., 110, B03403, doi:10.1029/2004JB003209, 2005.
Meade, B. J., and J. P. Loveless, Block modeling with connected fault-network geometries and a linear elastic coupling estimator in spherical coordinates, Bull. Seismol. Soc. Am., 99, 3124-3139, doi:10.1785/0120090088, 2009.
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Last modified Friday, 28-Jan-2011 21:10:25 UTC