SCEC Award Number 11106 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title NeoKinema models for UCERF3
Name Organization
Peter Bird University of California, Los Angeles
Other Participants Ivy Carpenter, graduate student
SCEC Priorities A1, A2, A3 SCEC Groups WGCEP, Geodesy, CDM
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Long-term-average rates of fault slip and distributed deformation were computed for California and surrounding regions to contribute deformation models for use in Uniform California Earthquake Rupture Forecast version 3 (UCERF3). We used documented kinematic finite-element code NeoKinema, which balances constraints from geodetic velocities, offset geologic features, principal stress directions, and Euler poles for relative plate motion. All models used an updated set of interseismic geodetic velocities, principal stress directions, a fixed Pacific-North America Euler vector, and a set of Quaternary geologic offset rates provided by other workers. Locking depths were fixed during the conversion of geodetic velocities from observed interseismic to estimated long-term rates. Two kinds of models were computed: (1) “block models,” based on a simplified geometry of selected faults; and (2) “fault-based models” with all the actual fault traces. In each case, two tuning parameters were adjusted to balance the fit to the input datasets, while avoiding computational instabilities. The best fits obtained to geodetic velocities were as good in absolute terms (RMS residual 2.3 mm/a; median 1.5 mm/a) as in previous published models, but this now represents a greater relative error (RMS of 4 sigma, vs. 2 sigma) due to the alleged halving of geodetic uncertainties. Other datasets can be fit at the two-sigma RMS level. Using additional assumptions and programs, we estimate that the revised preferred fault-based model (UCERF3064, using Fault Model 3.1) should yield long-term seismicity of which about 70% is generated on the model fault surfaces; about 30% is generated by distributed permanent deformation.
Intellectual Merit Modeling of neotectonics with "rigid" (purely-elastic) blocks/microplates has been a popular method for decades. However, it is difficult to assess how reasonable the underlying assumption is, or how it might influence model results. In this study we directly compare block- and fault-based models of the same region, using the same datasets. Among other results, we find that the block models actually require more distributed deformation than those which employ the actual fault network, at least if the geodetic velocities are to be fit at the same level in each class of model.
Broader Impacts The principal benefit to society is local, and derives from a more accurate representation of the spatial patterns of long-term fault slip rates and distributed deformation, which (in most cases) will be expressed as future seismicity. Compared to previous models such as UCERF2, the prediction of seismic hazard is significantly updated in areas such as the western Transverse Ranges and Santa Barbara Channel.
Exemplary Figure Figure 2. Long-term-average heave rates of faults in the California region, from fault-based model UCERF3064 using Fault Model 3.1. Width of fault ribbons is proportional to heave rate (averaged along each trace). Oblique heave is shown by double ribbons, with one color for the strike-slip component, and another for the strike-perpendicular component (e.g., Cascadia Trench).