Dynamic Issues in Fault- to-Fault Jumping David Oglesby UC Riverside UCERF3 Workshop June 11, 2011

Basic Idea What are some properties that affect the ability of rupture to jump a stepover? Can we still predict jump likelihood ahead of time?

Mechanism of Jumping Rupture

Harris and Day, 1993 Mechanism of Jumping Rupture

Harris and Day, 1993 Effect of Stepover Width, Direction, and Overlap/Gap

Harris and Day, 1993 Effect of Static Stress Level

Effect of Multiple Earthquake Cycles on Stress Stress (Mpa) Along Strike (km) 4 km Wide Compressional Stepover Duan and Oglesby (2006)

Effect of Stress/Slip Gradient at Fault Edge Oglesby, 2008

Effect of Stress/Slip Gradient at Fault Edge Elliott et al., 2009

Effect of Stress/Slip Gradient at Fault Edge Elliott et al., 2009

Linking Faults Magistrale and Day,1999

Linking Faults Lozos et al., 2011

Intermediate Faults No intermediate fault Lozos et al. 2011

Intermediate Faults 3 km long intermediate fault

Intermediate Faults 5 km long intermediate fault

Intermediate Faults 7 km long intermediate fault

Intermediate Faults 10 km long intermediate fault

Intermediate Faults 15 km long intermediate fault

Frictional Properties Fracture energy determines area of critical slipping region on secondary fault segment for nucleation. Higher fracture energy -> harder to nucleate rupture on secondary fault segment.

Summary Fault geometry Extensional stepovers (with overlaps!) are easier to jump than compressional ones. Narrower stepovers with overlaps facilitate jump. With linking faults, smaller angles and shorter connecting segments facilitate jump. Intermediate faults can facilitate or inhibit jump depending on size. Stress field Stress near failure, with strong stress gradient at edge of fault, facilitates jump. Frictional Properties Friction law is secondary effect; low fracture energy facilitates jump.

Conclusions There are many factors that influence whether rupture will jump a stepover, and what the slip will be on that fault system. We have only scratched the surface! Some factors may be known ahead of time [geometry, surface slip in past event(s)], some not. Dynamic (vs. static) analysis may be necessary in some cases. What is the predictability? Do the current results imply that a specific model of each stepover is necessary? Are there rules of thumb? Better knowledge of stress field around stepover is crucial, as is subsurface geometry. The observational results are telling us something about the physical parameters (geometry, stress, friction) on real faults.

Harris and Day, 1993 Effect of Overlap vs. Gap

Slip in Multi-Segment Rupture Willemse et al., 1996

Slip in Multi-Segment Rupture Willemse et al., 1996

Slip in Multi-Segment Rupture Kase, 2010