Influence of fault geometry on the spatial distribution of long-term slip with implications for determining representative fault slip rates

Phillip G. Resor, Michele L. Cooke, Scott T. Marshall, & Elizabeth H. Madden

Submitted September 22, 2017, SCEC Contribution #7921

Determining representative slip rates of active faults is essential to seismic hazard assessment and tectonic analysis. Here, we take a two-prong approach to determine how spatially variable slip over many earthquake cycles impacts geologic measurements of long-term slip rate. First, we use two-dimensional parametric models to estimate the probability that a point measurement is representative of the average slip rate for continuous strike-slip faults and those with a range of releasing stepover geometries and friction values. All models result in skewed distributions where a randomly selected site has a higher probability of sampling a slip rate that exceeds the mean. For most configurations, individual point measurements are unlikely (p < 0.5) to yield a slip rate within ±1 mm/yr of the mean. The probability can be notably improved (15-300%) by summing slip rates of overlapping segments. Second, we use three-dimensional mechanical models of a well-studied releasing stepover along the San Jacinto fault to investigate the impact of specific fault geometries on existing estimates of slip rate. Modeled dextral slip rates are 10-12 mm/yr along the southern portion of the San Jacinto Valley segment and the northern portion of the Anza segment, but decrease significantly along the southern portion of the Anza, Clark and Coyote Creek segments within the releasing stepover. These results are consistent with the abundant geologic slip rate data available for this system and serve to illustrate how site-specific models can be used to assess uncertainty associated with spatial variability of slip in fault systems with fewer measurements.

Key Words
slip rate, stepover, modeling

Citation
Resor, P. G., Cooke, M. L., Marshall, S. T., & Madden, E. H. (2017). Influence of fault geometry on the spatial distribution of long-term slip with implications for determining representative fault slip rates. Bulletin of the Seismological Society of America, (submitted).


Related Projects & Working Groups
Stress and Deformation Through Time (SDOT), Earthquake Geology, Tectonic Geodesy