SCEC Award Number 09158 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Physics-based earthquake scenarios for Yucca Mountain including off-fault damage
Name Organization
Jean-Paul Ampuero California Institute of Technology
Other Participants Javier Ruiz (post-doc)
SCEC Priorities A7, B2, B5 SCEC Groups Seismology, FARM, GMP
Report Due Date 02/28/2010 Date Report Submitted N/A
Project Abstract
This project aimed at developing physics-based earthquake scenarios that include the interaction between dynamic rupture and off-fault material damage (dynamic reduction of elastic moduli). The original target was to perform 2D spectral element simulations of earthquake scenarios for the Yucca Mountain site, and to compare the resulting seismic motions to previous models that assumed pure elasticity or off-fault plasticity. We addressed fundamental aspects of this complex problem by conducting work in three directions: the development of an improved formulation of the constitutive equations for continuum damage that allows the simulation of ruptures with high amounts of damage; the quantification of the effect of a pre-existing damaged fault zone structure on dynamic ruptures within the elastic regime; and the systematic quantification of the effects of off-fault plasticity on properties of dynamic ruptures that are relevant for strong ground motion prediction, including limits on extreme ground motions. Our key findings include the following. Rupture models with dynamic damage can induce complex patterns, including bimaterial effects and source modulation by fault zone trapped waves. Pre-existing fault zones can promote pulse-like rupture and rupture complexity. Off-fault plasticity can significantly contribute to seismic moment release and distort the moment tensor. We quantified how the properties of a low velocity fault zone and plastic response affect rupture behavior. We found a closed-form relation between peak slip velocity and rupture speed that can serve as a building block for pseudo-dynamic source representations for strong motion prediction.
Intellectual Merit The earthquake models developed here go beyond classical models by incorporating off-fault plastic deformation and rock damage. Our thorough parametric studies provide fundamental insight on these dynamic deformation mechanisms and systematically quantify their effect on source properties that are relevant for strong motion prediction. This research complements the information provided by more standard approaches for developing physical limits to extreme ground motion. The relations between source parameters found here are useful for the development of physics-based methods for strong ground motion prediction.
Broader Impacts The project provided training and research opportunities for a Caltech graduate student (Yihe Huang) and a visiting graduate student from ETH Zurich (Alice Gabriel). The project fostered collaboration with SCEC colleagues at USC (Y.Ben-Zion), including a USC graduate student (Shiqing Xu). Open source software for earthquake simulations was enhanced.
Exemplary Figure Figure 1: The top row shows the spatial-temporal distribution of slip rate in three simulations of dynamic rupture within a fixed low velocity fault zone with 50% velocity reduction and width of 2Lc. Rate-and-state dependent frictional properties are varied from (a) to (c) such that these ruptures in homogeneous media (without fault zone) would illustrate a range of behaviors from crack-like (a) to pulse-like (b and c) ruptures. For each simulation, the bottom row shows the slip rate, stress and frictional strength at a distance of 30Lc from the hypocenter. Oscillatory modulation of slip velocity is induced by interactions between dynamic rupture and waves trapped in the fault zone.