Is the CFM5.0 an Improvement? Evidence from Mechanical Models of the Western Transverse Ranges Region

Scott T. Marshall, Gareth J. Funning, & Susan E. Owen

Published August 10, 2016, SCEC Contribution #6605, 2016 SCEC Annual Meeting Poster #151

The SCEC Community Fault Model (CFM) is a widely-used product that has existed for well over a decade and has seen numerous revisions. As with all community-derived products, testing the accuracy and performance of the model is key to further development. To evaluate the ability for the CFM geometry to reproduce long term fault slip rates, we present results from geodetically-constrained mechanical models of the western Transverse Ranges, CA. To determine if the current CFM5.0 represents an improvement over the previous CFM4.0 and to identify the most likely geometry for the Ventura-Pitas Point fault system, we have created three models to compare to geologic slip rate estimates. The first model is based on CFM4.0, the second based on CFM5.0 with a flat ramp geometry for the Ventura-Pitas Point fault, and third, a CFM5.0 model with the Ventura-Pitas Point fault having a constant dip angle. To evaluate the performance of these three models, we compare the slip rates in the Uniform California Earthquake Rupture Forecast version 3 (UCERF3) to model-calculated average slip rates of each fault segment. We find that while all three models match the UCERF3 data well, the CFM4.0 model tends to produce slip rates that are skewed towards the fast ends of the geologic slip rate ranges. Despite significantly different subsurface geometries, the two CFM5.0 models both produce similar average reverse slip rates for the Ventura-Pitas Point fault of 3.1 and 3.4 mm/yr for the ramp and constant dip models, respectively. Analysis of the model-predicted surface slip distributions show that the existing geologic slip rate estimate of 4.4-6.9 mm/yr was likely made in a zone of faster than average slip along the fault. Because slip rates are spatially variable, we also compare each geologic slip rate point estimate to the model computed value at the fault element nearest to the study site. We find that when compared to model results, many existing geologic slip rate study sites are not likely to record average slip rates.

Key Words
Slip rates, fault, mechanical model, dislocation, geodesy, Community Fault Model, Ventura, Transverse Ranges

Citation
Marshall, S. T., Funning, G. J., & Owen, S. E. (2016, 08). Is the CFM5.0 an Improvement? Evidence from Mechanical Models of the Western Transverse Ranges Region. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy