SCEC Award Number 16268 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Southern California Kinematic and Dynamic Models: Calibration to the SCEC CSM and Assessment of Sensitivity to SAF Geometry
Investigator(s)
Name Organization
Elizabeth Hearn Capstone Geophysics
Other Participants
SCEC Priorities 1b, 1e, 2d SCEC Groups CISM, Geodesy, SDOT
Report Due Date 03/15/2017 Date Report Submitted 07/14/2017
Project Abstract
 During the past two years, I have developed several suites of kinematic models of southern California to investigate discrepancies between geodetic and geologic fault slip rates, and the extent of “off-fault” deformation (i.e., not due to locking of modeled faults). These models incorporate the UCERF3 block-bounding fault geometry and slip rates from the UCERF3 report (Field et al., 2013). Fault slip rates were randomly sampled from ranges given in the UCERF3 report, and models were scored by their misfit to GPS site velocities and total strain energy (TSE). Slip rates for major faults and the effect of viscoelastic perturbations to surface velocities are described in my 2015 project summary. The main emphasis for 2016 was estimating the proportion of deformation arising from non-modeled faults and/or plastic deformation of the upper crust (that is, not associated with interseismic locking of modeled faults). I find that off-fault deformation accounts for 23-32% of the total strain energy accumulation in southern California, depending on how it is calculated. This is consistent with previous estimates (e.g. Field et al., 2013, Johnson, 2013). Dynamic modeling work has targeted implementation of upper crustal plasticity and slippery-node faults with and without resolved shear tractions. Quantitative comparisons of dynamically modeled fault slip rates to geologic and kinematically modeled rates will begin after all of the faults are added to the model and (for the elastic case) the strain energy rate is comparable to the best unlocked kinematic models.
Intellectual Merit This project is directly addresses some of SCEC's most pressing scientific questions. It tackles questions about geologic-geodetic slip rate discrepancies, and the proportion of apparent moment accumulation in the upper crust that may be going into inelastic processes and/or minor faulting. The models also provide estimates of stressing rate and stress (respectively) for the SCEC CSM.
Broader Impacts This project is of societal benefit because of its connections to quantifying likelihoods and effects of southern California earthquakes. The kinematic component of this research contributes to understanding discrepancies in inferred slip rates on faults and the extent of "off fault" deformation. This information is necessary for rupture forecasts and seismic hazard analyses. The dynamic part of this project is geared toward understanding absolute crustal stresses, which are important for modeling the dynamics of rupture propagation (earthquake gates) and ground motions.
Exemplary Figure Figure 1. Southern California deformation models with traction-free San Andreas Fault in an elastic (a) or plastic (b) lithosphere. Panel (c) shows elastic model with traction-free San Andreas, San Jacinto and Garlock faults, and with other faults slipping at prescribed UCERF3 rates (Field et al., 2013). Blue to pink background indicates strain energy accumulation rate per unit volume. Total annual strain energy accumulation rate for (a) and (c) are 3.65e+19 J/yr and 2.7e+19 J/yr, respectively. This sum covers only the top 10 km of crust. The strain energy accumulation rate for the plastic model decreases over time but has not been calculated for the epoch shown (10,000 model years).