Text S1. DEM Modeling
In our implementation of the discrete-element-method (DEM), we simulate
an assemblage of discrete spherical particles that interact with each
other according to elastic-frictional (Hertz-Mindlin) contact law. We
introduce cohesion by adding a mechanical bond at interparticle contacts
(Morgan, 2015). This property can allow us to simulate cohesive
materials as may occur within the deeper accretionary prism. The more
frontal region of a prism is approximated as non-cohesive, i.e., lacking
interparticle bonds. The combination of pre-assigned interparticle
contact parameters, in combination with the mechanical properties of the
particles themselves, define the overall behavior of the particle
assemblage. This study uses a version of DEM implemented in RICEBAL.
Details about the method are provided in Morgan and Boettcher (1999),
Guo and Morgan (2004; 2006), and Morgan (2015). Continuum approximations
of the bulk properties and behavior of the numerical model are derived
using the contact force distribution and displacement gradients. By
averaging continuum properties over finite volumes, stress and strain
fields can be calculated for the domain (Thornton and Barnes, 1986;
Morgan and Boettcher, 1999; Morgan and McGovern, 2005a; 2005b; Morgan,
2015).
Figure 1 shows the general model setup. The initial length of the
simulated wedge is set to 200km, comparable to the dimensions of the
rupture lengths along the Chile Margin (Moreno et al. , 2010;
Contreras-Reyes et al. , 2017). To best balance model run time and
model resolution, the upper wedge is constructed of approximately
200,000 discrete particles with radii of 100, 120, 160 and 200 m.
Particles are randomly generated within a two-dimensional domain
400\(\times\)60 km, allowed to settle under gravity, and then trimmed to
the desired wedge geometry.
The mechanical properties of the simulated system are defined by the
assigned particle properties and interparticle friction coefficients
(Table S1 and Table S2). The gray particles defining the basal sliding
surface are fixed in space, their small radii (10 m) ensure a relatively
smooth sliding surface, unimpeded by particle roughness.
The contacts between particles, distinguished by labeled surface types
(Figure 1), is controlled by the interparticle friction coefficients.
The basal sliding surface is defined by Surface Type 4. The upper plate
as is partitioned into an inner (velocity-weakening) wedge (Surface Type
1) and outer (velocity-strengthening) wedge (Surface Type 3) domains.
The splay fault boundary defined by Surface Type 1 and Surface Type 2.
In addition, cohesiveness, as an option, can be implemented by adding
bonds to every contact to simulate more realistic cohesive material. The
mechanical properties of the domain and the fault interface are
controlled by the particle properties and interparticle friction
coefficients. To simulate a predefined fault, relatively low or zero
interparticle friction coefficients can be assigned to the particles
that define the fault interface, with no cohesion at the contacts
between those particles.