(sec-user-examples-reverse-2d-step08)= # Step 8: Slip on Two Faults and Power-law Viscoelastic Materials % Metadata extracted from parameter files. ```{include} step08_twofaults_powerlaw-synopsis.md ``` ## Simulation parameters In this example we replace the linear, isotropic Maxwell viscoelastic bulk rheology in the slab in Step 7 with an isotropic powerlaw viscoelastic rheology. The other parameters remain the same as those in Step 6. The parameters specific to this example are in `step08_twofaults_powerlaw.cfg`. ```{code-block} cfg --- caption: Power-law viscoelastic bulk rheology parameters for Step 8. --- [pylithapp.problem.materials] slab.bulk_rheology = pylith.materials.IsotropicPowerLaw [pylithapp.problem.materials.slab] db_auxiliary_field = spatialdata.spatialdb.CompositeDB db_auxiliary_field.description = Power law material properties bulk_rheology.auxiliary_subfields.power_law_reference_strain_rate.basis_order = 0 bulk_rheology.auxiliary_subfields.power_law_reference_stress.basis_order = 0 bulk_rheology.auxiliary_subfields.power_law_exponent.basis_order = 0 [pylithapp.problem.materials.slab.db_auxiliary_field] # Elastic properties values_A = [density, vs, vp] db_A = spatialdata.spatialdb.SimpleDB db_A.description = Elastic properties for slab db_A.iohandler.filename = mat_elastic.spatialdb # Power law properties values_B = [ power_law_reference_stress, power_law_reference_strain_rate, power_law_exponent, viscous_strain_xx, viscous_strain_yy, viscous_strain_zz, viscous_strain_xy, reference_stress_xx, reference_stress_yy, reference_stress_zz, reference_stress_xy, reference_strain_xx, reference_strain_yy, reference_strain_zz, reference_strain_xy, deviatoric_stress_xx, deviatoric_stress_yy, deviatoric_stress_zz, deviatoric_stress_xy ] db_B = spatialdata.spatialdb.SimpleDB db_B.description = Material properties specific to power law bulk rheology for the slab db_B.iohandler.filename = mat_powerlaw.spatialdb db_B.query_type = linear ``` ## Power-law spatial database *New in v4.0.0* We use the utility script `pylith_powerlaw_gendb` (see {ref}`sec-user-run-pylith-pylith-powerlaw-gendb`) to generate the spatial database `mat_powerlaw.spatialdb` with the power-law bulk rheology parameters. We provide the parameters for `pylith_powerlaw_gendb` in `powerlaw_gendb.cfg`, which follows the same formatting conventions as the PyLith parameter files. ```{code-block} console --- caption: Generate spatial database with power-law viscoelastic material properties. --- $ pylith_powerlaw_gendb powerlaw_gendb.cfg ``` ## Running the simulation ```{code-block} console --- caption: Run Step 8 simulation --- $ pylith step08_twofaults_powerlaw.cfg # The output should look something like the following. >> /software/unix/py3.12-venv/pylith-debug/lib/python3.12/site-packages/pylith/apps/PyLithApp.py:77:main -- pylithapp(info) -- Running on 1 process(es). >> /software/unix/py3.12-venv/pylith-debug/lib/python3.12/site-packages/pylith/meshio/MeshIOObj.py:38:read -- meshiopetsc(info) -- Reading finite-element mesh >> /src/cig/pylith/libsrc/pylith/meshio/MeshIO.cc:85:void pylith::meshio::MeshIO::read(pylith::topology::Mesh *, const bool) -- meshiopetsc(info) -- Component 'reader': Domain bounding box: (-100000, 100000) (-100000, 0) # -- many lines omitted -- 25 TS dt 0.2 time 4.8 0 SNES Function norm 2.142894303456e-06 Linear solve converged due to CONVERGED_ATOL iterations 22 1 SNES Function norm 6.320440892495e-09 Linear solve converged due to CONVERGED_ATOL iterations 14 2 SNES Function norm 1.048804327259e-10 Nonlinear solve converged due to CONVERGED_FNORM_ABS iterations 2 26 TS dt 0.2 time 5. >> /software/unix/py3.12-venv/pylith-debug/lib/python3.12/site-packages/pylith/problems/Problem.py:199:finalize -- timedependent(info) -- Finalizing problem. ``` As in Step 7, the simulation advances 26 time steps. With a nonlinear bulk rheology, the nonlinear solver now requires a few iterations to converge at each time step. ## Visualizing the results The `output` directory contains the simulation output. Each "observer" writes its own set of files, so the solution over the domain is in one set of files, the boundary condition information is in another set of files, and the material information is in yet another set of files. The HDF5 (`.h5`) files contain the mesh geometry and topology information along with the solution fields. The Xdmf (`.xmf`) files contain metadata that allow visualization tools like ParaView to know where to find the information in the HDF5 files. To visualize the data using ParaView or Visit, load the Xdmf files. In {numref}`fig:example:reverse:2d:step08:solution` we use ParaView to visualize the y displacement field using the `viz/plot_dispwarp.py` Python script. First, we start ParaView from the `examples/reverse-2d` directory. Before running the `viz/plot_dispwarp.py` Python script as described in {ref}`sec-paraview-python-scripts`, we set the simulation name in the ParaView Python Shell. ```{code-block} python --- caption: Set the simulation and exaggeration in the ParaView Python Shell. --- >>> SIM = "step08_twofaults_powerlaw" >>> FIELD_COMPONENT = "X" ``` :::{figure-md} fig:example:reverse:2d:step08:solution Solution for Step 8. The colors indicate the magnitude of the x displacement, and the deformation is exaggerated by a factor of 1000. Solution for Step 8 at t=100 years. The colors of the shaded surface indicate the magnitude of the x displacement, and the deformation is exaggerated by a factor of 1000. The undeformed configuration is show by the gray wireframe. Our parameters for the power-law bulk rheology result in much less viscoelastic relaxation in this case compared to Step 7. :::