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Off-Fault Secondary Failure Induced by a Dynamic Slip Pulse

¹ Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences
224 Pierce Hall, 29 Oxford Street
Harvard University
Cambridge, Massachusetts 02138
rice{at}esag.harvard.edu
 (J.R.R.)

² Department of Earth Sciences
University of Southern California
Los Angeles, California 90089-0740
sammis{at}usc.edu
 (C.G.S.)

³ Division of Engineering and Applied Sciences
Harvard University
Cambridge, Massachusetts 02138
rparsons{at}post.harvard.edu
 (R.P.)

^* Present address: Axiam, Inc., 1 Blackburn Center, Gloucester, Massachusetts 01930.

We develop a 2D slip-weakening description of a self-healing slip pulse that propagates dynamically in a steady-state configuration. The model is used to estimate patterns of off-fault secondary failure induced by the rupture, and also to infer fracture energies G for large earthquakes. This extends an analysis for a semi-infinite rupture (Poliakov et al., 2002) to the case of a finite slipping zone length L of the pulse. The dynamic stress drop, when divided by the drop from peak to residual strength, determines the ratio of L to the slip-weakening zone length R. Predicted off-fault damage is controlled by that scaled stress drop, static and dynamic friction coefficients, rupture velocity, principal prestress orientation, and poroelastic Skempton coefficient. All damage zone lengths can be scaled by , which is proportional G/(strength drop)² and is the value of R in the low-rupture-velocity, low-stress-drop, limit. In contrast to the Poliakov et al. (2002) case R/L = 0, the region that supports Coulomb failure reaches a maximum size on the order of when mode II rupture speed approaches the Rayleigh speed. Analysis of slip pulses documented by Heaton (1990) leads to estimates of G, each with a factor-of-two model uncertainty, from 0.1 to 9 MJ/m² (including the factor), averaging 2–4 MJ/m²; G tends to increase with the amount of slip in the event. In most cases, secondary faulting should extend, at high rupture speeds, to distances from the principal fault surface on the order of 1 to 2 1–80 m for a 100-MPa strength drop; that distance should vary with depth, being larger near the surface. We also discuss gouge and damage processes.

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