History

PyLith 1.0 was the first version to allow the solution of both implicit (quasistatic) and explicit (dynamic) problems and was a complete rewrite of the original PyLith (version 0.8). PyLith 1.0 combines the functionality of EqSim [Aagaard et al., 2001], [Aagaard et al., 2001] and PyLith 0.8. PyLith 0.8 was a direct descendant of LithoMop and was the first version that ran in parallel, as well as providing several other improvements over LithoMop. LithoMop was the product of major re-engineering of Tecton, a finite-element code for simulating static and quasistatic crustal deformation. The major new features present in LithoMop included dynamic memory allocation and the use of the Pyre simulation framework and PETSc solvers. EqSim was written by Brad Aagaard to solve problems in earthquake dynamics, including rupture propagation and seismic wave propagation.

The release of PyLith 1.0 has been followed by additional releases that expandthe number of features as well as improve performance. The PyLith 1.x series of releases allows the solution of both quasistatic and dynamic problems in one, two, or three dimensions. The code runs in either serial or parallel, and the design allows for relatively easy scripting using the Python programming language. Material properties and values for boundary and fault conditions are specified using spatial databases, which permit easy prescription of complex spatial variations of properties and parameters. Simulation parameters are generally specified through the use of simple ASCII files or the command line. At present, mesh information may be provided using a simple ASCII file (PyLith mesh ASCII format) or imported from CUBIT or Gmsh. The elements currently available include a linear bar in 1D, linear triangles and quadrilaterals in 2D, and linear tetrahedra and hexahedra in 3D. Materials presently available include isotropic elastic, linear Maxwell viscoelastic, generalized Maxwell viscoelastic, power-law viscoelastic, and Drucker-Prager elastoplastic. Boundary conditions include Dirichlet (prescribed displacements and velocities), Neumann (traction), point forces, and absorbing boundaries. Cohesive elements are used to implement slip across interior surfaces (faults) with both kinematically-specified fault slip and slip governed by fault constitutive models. PyLith also includes an interface for computing static Green’s functions for fault slip.

PyLith 2.0 replaced the finite-element data structures provided by the C++ Sieve implementation with those provided by the C DMPlex implementation. The newly developed DMPlex implementation by the PETSc developers conforms to the PETSc data manager (DM) interface, thereby providing tighter integration with other PETSc data structures, such as vectors and matrices. Other improvements include significantly reduced memory use and memory balancing.

PyLith 3.0 involves restructuring the code to permit more flexible specifications of governing equations and discretization and use of PETSc time-stepping algorithms. The finite-element integrations, constraints, and transformations are done through a suite of point-wise functions. The PETSc DMPlex interface calls these functions to perform the finite-element integrations.

PyLith is under active development and we expect a number of additions and improvements in the near future. Likely enhancements will include additional bulk and fault constitutive models, coupled quasistatic and dynamic simulations for earthquake cycle modeling, and coupling between elasticity, heat flow, and/or fluid flow.