SCEC Award Number 13178 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Weakening, strain localization, and the deep structure of the San Andreas Transform system
Investigator(s)
Name Organization
John Platt University of Southern California Thorsten Becker University of Southern California
Other Participants Rachel Lippoldt (research student)
Boris Kaus (collaborator)
SCEC Priorities 1, 2, 3 SCEC Groups SDOT, USR, EFP
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 The aim of this project is to continue our microstructural and numerical analysis of the evolution of lithospheric shear zones, applied specifically to southern California. We are developing a numerical model that includes the thermo-mechanics of an evolving, internally mechanically consistent fault system, incorporating the results of recent paleopiezometric studies of Southern California crust, and taking into account our theoretical work on the microstructural and rheological evolution of ductile shear zones. We have also worked on the contribution of dissipative heating to strain localization in shear zones with a width pre-defined by microstructural weakening, and on the feedback between thermal weakening and grain-growth in grain-size sensitive creep. Our results improve our understanding of the strength and structure of lithospheric shear zones beneath the seismogenic layer, and their interaction with the seismogenic faults that lie above them, and how faults are loaded at depth and behave over long times.
Intellectual Merit The overall goal of the modeling is to investigate strain localization required for plate boundary formation and maintenance. Lithospheric ductile shear zones exhibit complex rheologies that require to account for feedback mechanisms between mechanical and thermal behavior, as well as keep tracking of state variables such as grain size distributions. To this end, we seek to develop a flexible finite element framework based on open source software which will allow incorporating rheological complexities as well as material heterogeneity.
Broader Impacts The project partially supported USC graduate student Rachel Lippoldt.
Exemplary Figure Figure 1. Left: Non-dimensional example of the basic 3D model set up for an instantaneous viscous solution with an infinitely long strike slip fault. Velocity plot showing the amplitude of velocity are shown in color and the arrows show the direction of motion. Right: Map view of a non-dimensional example of the split node solution for an infinite fault. The split node fault is traced at x = 0.5. The colors represent imposed velocities that are assigned at the split nodes. The blue arrows show the direction of motion.