Role of fault geometry on the spatial distribution of the slip budget

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

Published August 3, 2016, SCEC Contribution #6490, 2016 SCEC Annual Meeting Poster #015

A fundamental problem in earthquake physics is how stress is transferred from plate motion to faults. Kinematic models assume that long-term fault slip rates will sum to the plate velocity; however, in a number of locations in southern California slip rates determined from modeling geodetic data in this manner differ significantly from geologic estimates. In this study we use mechanical models to investigate how releasing steps may affect estimates of fault slip over geologic time scales.

A suite of 2D models of idealized fault systems reveals how fault length, friction and step geometry affect kinematic efficiency of the system and the distribution of slip rate along the faults. We find that although systems with longer fault segments are more efficient, accommodating ~56-86% of plate displacement, point sampling of these systems during geologic studies is unlikely (p<50%) to yield representative slip rate estimates. Systems with short segments, although much less efficient, are more likely to yield representative slip rate estimates, particularly when slip on overlapping segments is summed.

A 3D model of the San Jacinto fault illustrates how fault system geometry may impact slip rate estimates along a real fault system. Modeled slip rates are faster in the middle of fault segments and slower within releasing steps, consistent with published geologic estimates. The mean slip rate along the modeled fault trace, however, is significantly slower than the simple average of the geological rates. Our results suggest that the location of geologic slip rate studies may govern their suitability for hazard estimates and that models can be used to put point measurements of slip into the context of slip distribution throughout a fault system.

Key Words
Fault geometry, slip rates, modeling, geodesy

Citation
Resor, P. G., Cooke, M. L., Marshall, S. T., & Madden, E. H. (2016, 08). Role of fault geometry on the spatial distribution of the slip budget. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)