# Step 4: Earthquake Cycle with Prescribed Slip This example combines the interseismic deformation from Step 3 and expands on the earthquake ruptures from Step 2. We expand the earthquake ruptures to span the entire along strike length of the top of the slab and also consider earthquake rupture on the splay fault. We use linear Maxwell viscoelastic bulk rheologies in the mantle and deeper part of the slab. {numref}`fig:example:subduction:3d:step04:diagram` shows the boundary conditions on the domain. :::{figure-md} fig:example:subduction:3d:step04:diagram Boundary conditions for quasi-static interseismic deformation. We prescribe aseismic slip (creep) on the bottom of the slab and the deeper portion of the top of the slab; the shallow portion of the top of the slab remains locked. ::: % Features extracted from simulation parameter files. ```{include} step04_eqcycle-synopsis.md ``` ## Simulation parameters The parameters specific to this example are in `step04_eqcycle.cfg` and include: * `pylithapp.metadata` Metadata for this simulation. Even when the author and version are the same for all simulations in a directory, we prefer to keep that metadata in each simulation file as a reminder to keep it up-to-date for each simulation. * `pylithapp` Parameters defining where to write the output. * `pylithapp.problem` Parameters for the time step information as well as solution field with displacement and Lagrange multiplier subfields. * `pylithapp.interfaces` Parameters for the earthquake ruptures and aseismic slip (creep) on the top and bottom of the slab. * `pylithapp.problem.bc` Parameters for describing the boundary conditions that override the defaults. We extend the duration of the simulation to 300 years. We impose two earthquake ruptures on slab interface at t=100 and t=200 years and one earthquake rupture on the splay fault at t=250 years. Now that we have both earthquake rupture and aseismic creep on the top of the slab, we use `SimpleDB` spatial databases to give depth-dependent, complementary slip. We impose uniform slip on the splay fault using a `UniformDB`. As in Step 3 we also adjust the nodesets used for the boundary conditions to remove overlap with the slab to allow the slab to move independently. Note that the aseismic slip uses `KinSrcConstRate`, while the two ruptures use the default `KinSrcStep`. ```{code-block} console --- caption: Run Step 4 simulation --- $ pylith step04_eqcycle.cfg mat_viscoelastic.cfg # The output should look something like the following. >> /software/py38-venv/pylith-opt/lib/python3.8/site-packages/pylith/meshio/MeshIOObj.py:44:read -- meshiocubit(info) -- Reading finite-element mesh >> /pylith/libsrc/pylith/meshio/MeshIOCubit.cc:157:void pylith::meshio::MeshIOCubit::_readVertices(pylith::meshio::ExodusII&, pylith::scalar_array*, int*, int*) const -- meshiocubit(info) -- Component 'reader': Reading 24824 vertices. >> /pylith/libsrc/pylith/meshio/MeshIOCubit.cc:217:void pylith::meshio::MeshIOCubit::_readCells(pylith::meshio::ExodusII&, pyl ith::int_array*, pylith::int_array*, int*, int*) const -- meshiocubit(info) -- Component 'reader': Reading 134381 cells in 4 blocks. # -- many lines omitted -- >> /pylith/libsrc/pylith/utils/PetscOptions.cc:235:static void pylith::utils::_PetscOptions::write(pythia::journal::info_t&, const char*, const pylith::utils::PetscOptions&) -- petscoptions(info) -- Setting PETSc options: fieldsplit_displacement_ksp_type = preonly fieldsplit_displacement_mg_levels_ksp_type = richardson fieldsplit_displacement_mg_levels_pc_type = sor fieldsplit_displacement_pc_type = gamg fieldsplit_lagrange_multiplier_fault_ksp_type = preonly fieldsplit_lagrange_multiplier_fault_mg_levels_ksp_type = richardson fieldsplit_lagrange_multiplier_fault_mg_levels_pc_type = sor fieldsplit_lagrange_multiplier_fault_pc_type = gamg ksp_atol = 1.0e-12 ksp_converged_reason = true ksp_error_if_not_converged = true ksp_rtol = 1.0e-12 pc_fieldsplit_schur_factorization_type = lower pc_fieldsplit_schur_precondition = selfp pc_fieldsplit_schur_scale = 1.0 pc_fieldsplit_type = schur pc_type = fieldsplit pc_use_amat = true snes_atol = 1.0e-9 snes_converged_reason = true snes_error_if_not_converged = true snes_monitor = true snes_rtol = 1.0e-12 ts_error_if_step_fails = true ts_monitor = true ts_type = beuler # -- many lines omitted -- 30 TS dt 0.1 time 2.9 0 SNES Function norm 8.197330252849e+00 Linear solve converged due to CONVERGED_ATOL iterations 416 1 SNES Function norm 4.780619312733e-10 Nonlinear solve converged due to CONVERGED_FNORM_ABS iterations 1 31 TS dt 0.1 time 3. >> /software/baagaard/py38-venv/pylith-opt/lib/python3.8/site-packages/pylith/problems/Problem.py:201:finalize -- timedependent(info) -- Finalizing problem. ``` The beginning of the output is near the same as in Steps 2 and 3. The simulation advances 31 time steps. As in Step 3 each linear solve requires about 400 iterations to converge. ## Visualizing the results In {numref}`fig:example:subduction:3d:step04:solution` we use the `pylith_viz` utility to visualize the x displacement field. You can move the slider or use the `p` and `n` keys to change the increment or decrement time. ```{code-block} console --- caption: Visualize PyLith output using `pylith_viz`. --- pylith_viz --filename=output/step04_eqcycle-domain.h5 warp_grid --component=x --exaggeration=5000 ``` :::{figure-md} fig:example:subduction:3d:step04:solution Solution for Step 4 at t=100 yr. The colors indicate the x displacement, and the deformation is exaggerated by a factor of 5000. Solution for Step 4 at t=100 yr. The colors of the shaded surface indicate the x displacement, and the deformation is exaggerated by a factor of 5000. :::