SCEC Award Number 16048 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Tuning Dynamic Models to Estimate Varying Fault Friction, Asthenospheric Traction, and Lithospheric Stress
Investigator(s)
Name Organization
Peter Bird University of California, Los Angeles
Other Participants
SCEC Priorities 2d, 3d, 4b SCEC Groups CME, WGCEP, SDOT
Report Due Date 03/15/2017 Date Report Submitted 02/23/2017
Project Abstract
Two kinds of thin-shell finite-element model of neotectonics exist: (1) kinematic models which fit geodetic and geologic data, but use little physics; and (2) dynamic models that use realistic rheologies and stress-equilibrium, but don’t match kinematic data. A dynamic model can be tuned by: (A) adjusting horizontal shear tractions on the base of the lithosphere; or (B) adjusting the friction of each fault. I adjusted a Shells dynamic model to better match long-term flow and slip-rates from the NeoKinema deformation model of UCERF3. In method (A), I defined 31 microplates based on long-term velocities in the NeoKinema solution. Then I used an iterated-solution method to adjust basal tractions on 23 microplates. At best, the model with fault friction 0.04 reduced RMS fault slip-rate errors from 4.87 to 2.98 mm/a; however, required basal shear tractions were implausible (to 100 MPa) and also implausible in pattern. In method (B), the Shells solution was revised 100 times, and each time the effective friction of 1000 fault elements was adjusted up or down based on the current sense of slip-rate error. Over 60% of fault elements reached the lower friction limit of 0.01. RMS error in slip-rates fell from 5.69 to 1.55 mm/a. My interpretation is that ~60% of active fault area in southern California experiences near-total stress-drop in large earthquakes due to dynamic weakening. Yet, other areas retain higher effective friction and serve as nucleation sites. All results are tentative because the planned Community Thermal Model and Rheology Model were not yet available.