Text S2. Simulation
Workflow
We seek to simulate the dynamic Coulomb Wedge model earthquake cycle
(Wang and Hu, 2006) in our simulations. We first prepare the fault for
dynamic slip by preconditioning it during steady backwall displacement,
holding the initial basal friction at 0.04. This represents the
interseismic stage. This preconditioning ensures high shear stress along
the fault and the accumulation of elastic strain energy within the
wedge. To simulate the dynamic stage of the earthquake cycle, we reduce
the friction coefficient along the basal decollement beneath the inner
wedge to approximate velocity weakening and either increase or maintain
the basal friction beneath the outer wedge to approximate velocity
strengthening. the internal friction coefficient is maintained at 0.30
for both the inner and outer wedges.
During the pre-earthquake loading stage, the right wall of the wedge
moves inward at a constant horizontal velocity (vx) of 1
m/s, under constant basal friction conditions. During this
preconditioning stage, the system state is recorded at increments of 200
m of backwall displacement. The internal stresses within the wedge are
supported by elastic deformation at interparticle contacts, defining the
potential energy of the system. During this stage, the wedge deforms,
either extending or contracting, depending on the basal friction
conditions and the predefined wedge geometry. The preconditioning stage
is complete when the model reaches its steady state, State 1. Details
about the implementation of preconditioning and the discussion about the
steady state can be found in Wang and Morgan (2019).
Once the wedge reaches State 1, we simulate the second stage of dynamic
earthquake unloading, culminating in the final State 2. At the start of
the second stage, backwall displacement is stopped. Earthquake unloading
is initiated by the reduction in basal friction beneath the inner wedge,
and concurrent increase in friction beneath the outer wedge as
appropriate.
For each model, a splay fault with a dip, varying from landward to
seaward dipping is prescribed just before the earthquake unloading. A
model without any prescribed splay fault is also constructed as a
reference.
Table S1 Basal Friction Conditions along Megathrust and Splay Fault
before and after Earthquake Unloading.