# Step 2: Quasistatic Interseismic Deformation
% Features extracted from simulation parameter files.
```{include} step02_interseismic-synopsis.md
```
## Simulation parameters
In this example we simulate the interseismic deformation associated with the oceanic crust subducting beneath the continental crust and into the mantle.
We prescribe steady aseismic slip of 8 cm/yr along the interfaces between the oceanic crust and mantle with the interface between the oceanic crust and continental crust locked as shown in {numref}`fig:example:subduction:2d:step02:diagram`.
The parameters specific to this example are in `step02_interseismic.cfg`.
:::{figure-md} fig:example:subduction:2d:step02:diagram
Boundary conditions for quasistatic simulation for interseismic deformation.
We prescribe constant creep on the top and bottom of the subduction slab, except for the portion of the subduction interface where we imposed coseismic slip in Step 1.
We lock (zero creep) that part of the interface.
:::
The simulation spans 150 years with an initial time step of 5 years.
```{code-block} cfg
---
caption: Time stepping parameters for Step 2.
---
[pylithapp.timedependent]
initial_dt = 5.0*year
start_time = -5.0*year
end_time = 150.0*year
```
We create an array with 2 faults, one for the top of the slab and one for the bottom of the slab.
We use the constant slip rate kinematic source model with a uniform slip rate on the bottom of the slab and a slip rate that varies with depth on the top of the slab.
```{code-block} cfg
---
caption: Prescribed slip parameters for Step 2.
---
[pylithapp.problem]
interfaces = [fault_slabtop, fault_slabbot]
[pylithapp.problem.interfaces.fault_slabtop]
label = fault_slabtop
label_value = 21
edge = fault_slabtop_edge
edge_value = 31
observers.observer.data_fields = [slip]
[pylithapp.problem.interfaces.fault_slabtop.eq_ruptures]
rupture = pylith.faults.KinSrcConstRate
[pylithapp.problem.interfaces.fault_slabtop.eq_ruptures.rupture]
db_auxiliary_field = spatialdata.spatialdb.SimpleDB
db_auxiliary_field.description = Fault rupture auxiliary field spatial database
db_auxiliary_field.iohandler.filename = fault_slabtop_creep.spatialdb
db_auxiliary_field.query_type = linear
[pylithapp.problem.interfaces.fault_slabbot]
label = fault_slabbot
label_value = 22
edge = fault_slabbot_edge
edge_value = 32
observers.observer.data_fields = [slip]
[pylithapp.problem.interfaces.fault_slabbot.eq_ruptures]
rupture = pylith.faults.KinSrcConstRate
[pylithapp.problem.interfaces.fault_slabbot.eq_ruptures.rupture]
db_auxiliary_field = spatialdata.spatialdb.UniformDB
db_auxiliary_field.description = Fault rupture auxiliary field spatial database
db_auxiliary_field.values = [initiation_time, slip_rate_left_lateral, slip_rate_opening]
db_auxiliary_field.data = [0.0*year, 8.0*cm/year, 0.0*cm/year]
```
We adjust the Dirichlet (displacement) boundary conditions on the lateral edges and bottom of the domain by pinning only the portions of the boundaries that are mantle and continental crust and not oceanic crust.
```{code-block} cfg
---
caption: We use only 3 Dirichlet boundary conditions to allow the slab to move freely on the boundaries.
---
[pylithapp.problem]
bc = [bc_east_mantle, bc_west, bc_bottom]
```
## Running the simulation
```{code-block} console
---
caption: Run Step 2 simulation
---
$ pylith step02_interseismic.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:
(-600000, 600000)
(-600000, 399.651)
# -- many lines omitted --
30 TS dt 0.05 time 1.45
0 SNES Function norm 5.747931631477e-02
Linear solve converged due to CONVERGED_ATOL iterations 4
1 SNES Function norm 5.115112326356e-12
Nonlinear solve converged due to CONVERGED_FNORM_ABS iterations 1
31 TS dt 0.05 time 1.5
>> /software/unix/py3.12-venv/pylith-debug/lib/python3.12/site-packages/pylith/problems/Problem.py:199:finalize
-- timedependent(info)
-- Finalizing problem.
```
The beginning of the output written to the terminal is identical to that from Step 1.
At the end of the output, we see that the simulation advanced the solution 31 time steps.
Remember that the PETSc TS monitor shows the nondimensionalized time and time step values.
## Visualizing the results
In {numref}`fig:example:subduction:2d:step02:solution` we use ParaView to visualize the x displacement field using the `viz/plot_dispwarp.py` Python script.
First, we start ParaView from the `examples/subduction-2d` directory.
Next, we override the default name of the simulation file with the name of the current simulation.
```{code-block} python
---
caption: Set the simulation in the ParaView Python Shell.
---
>>> SIM = "step02_interseismic"
```
Finally, we run the `viz/plot_dispwarp.py` Python script as described in {ref}`sec-paraview-python-scripts`.
:::{figure-md} fig:example:subduction:2d:step02:solution
Solution for Step 2 at t=100 yr.
The colors of the shaded surface indicate the magnitude of the x displacement, and the deformation is exaggerated by a factor of 1000.
:::