Fault-zone healing effectiveness and the structural evolution of strike-slip fault systems

Abstract

SUMMARY Numerical simulations of long‐term crustal deformation reveal the important role that damage healing (i.e. fault‐zone strengthening) plays in the structural evolution of strike‐slip fault systems. We explore the sensitivity of simulated fault zone structure and evolution patterns to reasonable variations in the healing‐rate parameters in a continuum damage rheology model. Healing effectiveness, defined herein as a function of the healing rate parameters, describes the post‐seismic healing process in terms of the characteristic inter‐seismic damage level expected along fault segments in our simulations. Healing effectiveness is shown to control the spatial extent of damage zones and the long‐term geometrical complexity of strike‐slip fault systems in our 3‐D simulations. Specifically, simulations with highly effective healing form interseismically shallow fault cores bracketed by wide zones of off‐fault damage. Ineffective healing yields deeper fault cores that persist throughout the interseismic interval, and narrower zones of off‐fault damage. Furthermore, highly effective healing leads to a rapid evolution of an initially segmented fault system to a simpler through‐going fault, while ineffective healing along a segmented fault preserves complexities such as stepovers and fault jogs. Healing effectiveness and its role in fault evolution in our model may be generalized to describe how heat, fluid‐flow and stress conditions (that contribute to fault‐zone healing) affect fault‐zone structure and fault system evolution patterns.

Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

“…Hence, the damage associated with, and able to be healed with, individual seismic cycles is minor compared to permanent damage occurring close to the fault core in the mature faults studied. The efficiency of healing is thought to relate to the fault segmentation with unsegmented faults demonstrating well developed, enduring damage zones and fault rocks [ Finzi et al ., ].…”

Near‐surface versus fault zone damage following the 1999 Chi‐Chi earthquake: Observation and simulation of repeating earthquakes

“…Our work contrasts with numerical simulations of long‐term crustal deformation by Finzi et al . [], which show that localized fault damage along the active fault cores (strike‐slip fault) may rapidly heal at depth, while distributed off‐fault damage at the shallow depth is more sustained over time. Dynamic rupture propagation model predicts a wider damage at the shallow depth with slower healing rate; at deeper part the damage is more localized with faster healing rate, assuming cracks opening and closing as the same mechanisms for coseismic and postseismic damage [ Ma , ].…”

Damage in step‐overs may enable large cascading earthquakes

“…The faults are embedded in a homogeneous material with a constant, uniform damage level prescribed within the step‐over zone to represent weakened material. Application of non‐evolving damage is appropriate for our simulations of large off‐fault damage zones at seismogenic depth, as these zones are not expected to significantly heal after the post‐seismic stage [ Finzi et al , 2011; Ben‐Zion and Sammis , 2003] nor are they expected to accumulate much damage in a single earthquake [ Finzi et al , 2009; Ben‐Zion and Sammis , 2003].…”

“…Fault step‐overs are typically damaged by distributed fractures, veins, and other deformation features that reduce the strength of rocks and introduce stress concentrations. While faults typically exhibit rapid post‐seismic healing at depth, step‐over zones do not fully heal and rather display persistent, extensive damage and strain hardening throughout the seismogenic crust [ Finzi et al , 2011; Ben‐Zion and Sammis , 2003]. Such deep, damage‐zones, the lasting results of many previous earthquakes, were recently observed in the Eastern California Shear Zone [ Cochran et al , 2009].…”