SCEC Award Number 13134 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Investigation of Fault-to-Fault Predictions and Results from UCERF-3
Investigator(s)
Name Organization
Glenn Biasi University of Nevada, Reno
Other Participants none
SCEC Priorities 4, 2, 6 SCEC Groups WGCEP, SDOT, Geology
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 To construct ruptures for input to the Uniform California Earthquake Rupture Forecast 3, plausibility rules are applied between adjacent subsections. Once admitted, ruptures with steps and bends are considered equally likely in the input to the Grand Inversion as ruptures without them. At the same time, geologic observation and kinematic and dynamic modeling confirm that steps and bends reduce the likelihood of rupture propagation. This project develops empirical estimates of relative rupture probability from fault geometry and compares them to UCERF3 solution rates.

Empirical rupture probability at steps of width d are estimated in three ways, as a constant p(d) = 0.5 for d >1 km, as an exponential term p(d)=exp(d/r0) (r0=1.44 to match the step penalty at 1 km), and as a power law p(d) = 1/d^2, only applied if d>=1.0 km. Bends stop ruptures with an efficiency that depends on the bend angle. Two bend models are provided, and the least restrictive model is applied. As an example, ruptures with three steps greater than 1 km or three bends of 30 degrees are predicted to have an order of magnitude lower probability than ruptures having no steps or bends. At this level of complexity we find limited correspondence between UCERF3 rupture rates and empirical predictions. Physically, this should not be. Empirical probabilities from rupture complexity can be used to improve UCERF4 as a priori adjustments to help constrain the inversion, and to weed out ruptures so improbable that they will not affect hazard.
Intellectual Merit We have developed the first of its kind method to measure rupture complexity and applied it to the Uniform California Earthquake Rupture Forecast version 3. This work shows that the current rupture forecast for California is insensitive to complexity, as could be expected from its input equation set. Complexity reduces the rate of occurrence of real ruptures; integration of complexity measures in new inversions could improve future rate estimates.
Broader Impacts This work opens the way to include rupture complexity in future forecasts of earthquake rates, including for California. Improved probability estimates help reduce losses to earthquake hazards. As such it can contribute to improving collaborations with the California Earthquake Authority and the California risk estimation community.
Exemplary Figure Figure 2. Caption: Grand Inversion (GI) probabilities for ruptures 80-100 km long. Red is all from FM3.1 in this set. Other curves are the GI probabilities for the fraction considered complex ruptures by three empirical models of complexity. The GI does not penalize ruptures in the subset for their complexity.