Dynamic rupture modeling to investigate the role of fault geometry in jumping rupture between parallel-trace thrust faults

Paul L. Peshette, Julian C. Lozos, Doug Yule, & Eileen L. Evans

Published August 13, 2018, SCEC Contribution #8436, 2018 SCEC Annual Meeting Poster #209

Fold and thrust belts (such as those found in the Himalaya or California Transverse Ranges) consist of many neighboring thrust faults in a variety of geometries. Active thrusts within these areas individually contribute to regional seismic hazard, but there is also possibility of multi-fault rupture in a single event. Investigations of historic thrust surface traces suggest that within a single event rupture can jump from one fault to a separate fault up to 8 km away. There is also observational data of jumps occurring between thrust faults ~50 km apart. In contrast, previous modeling studies of thrust faults find a maximum jumping rupture distance of merely 0.2 km. Here, we present a new dynamic rupture modeling parameter study that attempts to reconcile these differences and determine which geometric and stress conditions promote jumping rupture. We use a community-verified 3D finite element method to model rupture on pairs of thrust faults with parallel surface traces and opposite dip orientations. We vary stress drop and the dimensionless strength ratio to determine which conditions produce jumping rupture at different dip angles and different minimum distance between faults. We find that geometry plays an essential role in determining whether or not rupture will jump to a neighboring thrust fault. Rupture is more likely to jump in faults oriented dipping toward one another at steeper angles, and the behavior tapers down to no rupture jump in shallow dip cases. Our variations of stress parameters emphasize these toward-orientation results. Rupture jump in faults dipping away from one another is complicated by variations of stress conditions, but the most prominent consistency is that for mid-dip angle faults rupture rarely jumps. In most of our models, rupture does not jump beyond 3 km, while some reach 5 km, and in one unique dipping away case rupture jumps beyond 20 km (potentially much farther). If initial stress conditions are such that they are already close to failure the possibility of a long distance jump increases. Our models call attention to specific geometric and stress conditions where the dynamic rupture front is most important to potential for jump. However, our models also highlight the importance of near-field stress changes due to slip. According to our modeling, the potential for rupture to jump is strongly dependent on both dip angle and orientation of faults.

Key Words
dynamic rupture modeling, thrust faults, reverse faults, jumping rupture, doublet, parameter study, stepover, triggered slip, fault geometry, renucleation

Citation
Peshette, P. L., Lozos, J. C., Yule, D., & Evans, E. L. (2018, 08). Dynamic rupture modeling to investigate the role of fault geometry in jumping rupture between parallel-trace thrust faults. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)