3D Simulations of Earthquakes on Parallel Offset Faults with Homogeneous Stress Conditions

Kayla A. Kroll, Keith B. Richards-Dinger, James H. Dieterich, & David D. Oglesby

Published August 1, 2017, SCEC Contribution #7378, 2017 SCEC Annual Meeting Poster #165

Several recent large earthquakes including the 2002 Mw7.9 Denali, Alaska, 2010 Mw7.2 El Mayor-Cucapah, Mexico, and the 2016 Mw7.8 Kaikoura, New Zealand events ruptured up to a dozen fault segments. Understanding how ruptures are able to jump across geometrical complexities is of critical importance for estimates of seismic hazard and earthquake forecasting, as earthquake magnitudes are largely affected by total rupture length. Large event clusters such as the Landers-Big Bear-Hector Mine sequence in California and the 2011 series of large events in Christchurch, New Zealand are of additional concern in forecasting and hazard analysis. In this work, we employ two earthquake rupture codes (FaultMod and RSQSim) to investigate the characteristics of rupture propagation (e.g. stress drop, slip, renucleation location, and maximum jump distance) across parallel strike-slip faults with uniform initial stresses at increasingly larger offsets. We also explore the possibility that time-dependent nucleation effects inherent to rate-state friction cause individual fault segments slip as part of a large event cluster, rather than in a single jumping rupture at larger offsets. We perform this analysis for fault systems classified by high (S=0.49) and low (S=1.25) initial stress states.

We show that results from RSQSim compare favorably with those from FaultMod. We find that the average slip is inversely related to offset in both simulations, however, slip is largely asymmetric in FaultMod. Average source and receiver fault stress drops vary considerably with larger offsets. Receiver fault renucleation locations lie within lobes of increased static stress for extensional and compressional offsets. For models with low stresses, the maximum jump distance is ~0.5 km for both simulation methods. For models with high stresses, FaultMod simulations jump larger offsets (~3km) than those produced with RSQSim (~2 km). However, when large event clusters are considered in RSQSim, the maximum jump distances increase and are nearly equal to those in FaultMod. These results indicate that 1) RSQSim is capable of producing ruptures similar to those of the fully dynamic simulations, 2) rupture characteristics vary as a function of offset, and 3) time-dependent nucleation allows for larger jump distances. This work suggests that large event clustering due time-dependent rupture effects should also be considered in earthquake forecasts and seismic hazard analysis.

Key Words
RSQSim, stepovers, jumping ruptures, earthquake simulation, dynamic rupture

Citation
Kroll, K. A., Richards-Dinger, K. B., Dieterich, J. H., & Oglesby, D. D. (2017, 08). 3D Simulations of Earthquakes on Parallel Offset Faults with Homogeneous Stress Conditions. Poster Presentation at 2017 SCEC Annual Meeting.

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