Hi all,
Hope you are doing great.
I have a system of faults in the middle of a plate and I’m going to impose some boundary condition (left lateral movement to the boundary of the plate) and see how the faults within the plate are reacting to this moveme
nts. You can see the image below for more clarification. My question is, can PyLith do that?
I assume you want to impose fault friction on the faults. PyLith v2 has this capability. PyLith v3 and later do not yet have fault friction, only prescribed slip. PyLith can only handle the fault geometry you show in your diagram if the fault intersections are T intersections. That is, you can have one through-going fault, but the other fault must end where it intersects the through-going fault. For the simple problem you show, I recommend starting in 2D and then going to 3D only if necessary.
This is not what we want to do, which is to find the response of a frictionless fault to an applied stress or strain field. This can be done by the code 3D-DEF of Gomberg and Ellis (1993) that performs elastic dislocation boundary-element calculations using Okada’s (1992) subroutines. The boundary element method permits one to examine, for example, how a fault will slip in response to applied stresses.
Unfortunately, Okada’s codes are limited to rectangular elements in a homogeneous half-space. We want to examine the deformation of the South Georgia continental block, sandwiched between the South America plate on the north and the Scotia plate on the south, along the strike-slip North Scotia Ridge. 3D-DEF can do this for a homogeneous model, but we would like to include the strength and crustal structure differences between the continental and oceanic components. The model consists of a large block whose boundary conditions are the plate movements and we would like to calculate the surface deformations due to the plate motions for the locked strike-slip faults for both the ocean-ocean and ocean-continent segments.
The model looks something like the image below. The dashed lines are the surface outcrops of the strike slip plate boundary and the / and \ are the restraining and releasing bends associated with the boundaries of the S. Georgia block sandwiched between them. The boundary condition on the plate boundaries is that they are locked from the surface to some locking depth with a freely slipping fault to the bottom of the model below the locking depth. We have done this using 3D-DEF with vertical faults restricted from opening and get the usual strike-slip deformation patterns for a homogeneous medium across the plate boundaries. We did it for S. Georgia’s boundaries being completely locked on the north only(no freely slipping fault to the base of the model, so attached to S. America), completely locked on the south only (being part of Scotia) and both north and south boundaries being free below a locking depth (independent). We want to do it with inhomogeneous material properties and non-rectangular faults. We have also done it in the free, performance limited, student version of Abaqus, which demonstrates it can be done, but we do not have access to the full version.
< ---------------------
South America Plate
/-------------------------\
--------------------------------------/ ---------------------------------------------
\ S. Georgia block /
\------------------------/
Scotia Plate
------------------- >
J.S. Gomberg and Michael Ellis, 1993, 3D-DEF; a user’s manual (a three-dimensional, boundary element modeling program), Open-File Report 93-547
Yoshimitsu Okada; Internal deformation due to shear and tensile faults in a half-space. Bulletin of the Seismological Society of America 1992; 82 (2): 1018–1040. doi: https://doi.org/10.1785/BSSA0820021018
Thank you for providing additional details.
The fault formulation with friction includes the case where the friction is zero. For faults locked above some depth, I would use a high static coefficient of friction in those regions and then a lower or zero coefficient of friction in the “freely slipping” regions.
PyLith supports variation in the parameters for bulk and fault constitutive models using spatial databases as described in the manual and demonstrated in the example suite.