SCEC Award Number 13037 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Dynamic Ruptures with Off-Fault Brittle Damage Accounting for Changes of Elastic Moduli
Name Organization
Yehuda Ben-Zion University of Southern California
Other Participants One Graduate Student
SCEC Priorities 3, 4 SCEC Groups Seismology, FARM, GMP
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
The spontaneous generation of brittle rock damage near and behind the tip of a propagating rupture can produce dynamic feedback mechanisms that modify significantly the rupture properties, seismic radiation and generated fault zone structure. In this project we study such feedback mechanisms for single rupture events and their consequences for earthquake physics and various possible observations. This is done through numerical simulations of in-plane dynamic ruptures on a frictional fault with bulk behavior governed by a brittle damage rheology that incorporates reduction of elastic moduli in off-fault yielding regions. The model simulations produce several features that modify key properties of the ruptures, local wave propagation and fault zone damage. These include (1) dynamic generation of near-fault regions with lower elastic properties, (2) dynamic changes of normal stress on the fault, (3) rupture transition from crack-like to a detached pulse, (4) emergence of a rupture mode consisting of a train of pulses, (5) quasi-periodic modulation of slip rate on the fault, and (6) asymmetric near-fault ground motion with higher amplitude and longer duration on the side with reduced elastic moduli. The results can have significant implications to multiple topics ranging from rupture directivity and near-fault seismic motion to tremor-like signals.
Intellectual Merit The study provides, through theoretical and computational modeling, quantitative predictions of the impact of off-fault brittle damage and geometrical fault complexities (and feedback mechanisms associated with these features) on observable properties of earthquake rupture, seismic wave radiation and short-term evolution of fault zone structure. The results provide improved guidelines for interpreting observed properties of rock damage near faults in terms of the generating mechanisms and regional/dynamic stress fields.
Broader Impacts The study addresses directly the science priority objectives 3c, 3e, 4b (as well as 3d and 5d) as articulated in those items and elaborations under the FARM group. The studies will also contribute to goals of the GMP group, SDOT group and special project CME.

The obtained results on various characteristics of off-fault damage provide target signals for earthquake and fault zone geologists. The developed extended formulation of the damage model can be useful for additional studies by other investigators.
Exemplary Figure Fig. 3.

Example results on (a) evolving shear wave speed normalized by the initial value, (b) associated normalized fault-normal particle velocity, and (c) normalized stress change near the rupture front. As shown in (c), there are alternating normal stress changes behind the rupture front, generally with opposite signs on different sides of the fault. The position of the first tensile normal stress change regime behind the rupture front (on the fault and to the compressional side) generally coincides with the location where a fresh LVZ has just formed (a).

From Xu, S., Ben-Zion, Y., Ampuero, J.-P. and Lyakhovsky, V., 2014.