SCEC Award Number 11065 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Earthquake nucleation mechanisms and damage in heterogeneous fault zones, probed with periodic loadings (in models, observations, and experiments)
Investigator(s)
Name Organization
Karin Dahmen University of Illinois at Urbana Champaign Yehuda Ben-Zion University of Southern California
Other Participants 2 students (one of them Braden Brinkman)
SCEC Priorities A3, A4, A10 SCEC Groups FARM, EFP, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 It has long been speculated that tidal stresses can trigger large earthquakes. However, experimental confirmation remains controversial, and theoretical models have yet to accurately predict the response of faults to external periodic stresses [T.H. Jordan, et al., Living on an Active Earth: Perspectives on Earthquake Science, National Academy Press, Washington, D.C., 418 pp., (2003)]. We studied a simple model for potential triggering mechanisms of large earthquakes in response to a slowly increasing loading stress and an added periodic stress with amplitude F0(ω) at frequency ω. The model predicts the minimum amplitude F0min(ω) needed to observe stress-correlated triggering of large slip-events in earthquake-fault-zones [Y. Ben-Zion, Reviews of Geophys. 46, RG4006 (2008)], sheared lab-scale rocks [Lockner and Beeler, J. Geophys. Res. 104, 20133 (1999) and 108, ESE 8-1 (2003)], and sheared granular materials [H. M. Savage, C. Marone, J. Geophys. Res. 112, B02301 (2007)]. We predict F0min(ω) ~ 1/ω for small (non-zero) frequencies and decaying oscillations for F0min(ω) for large frequencies. The predictions explain and unify disparate experimental results. We also argue that correlations between small slips and periodic stresses increase as the system approaches a large slip-event/earthquake. These result provide new tools for materials-failure prediction and hazard-prevention studies, applicable to a wide variety of systems [K. A. Dahmen, Y. Ben-Zion, J. T. Uhl, Phys. Rev. Lett. 102, 175501 (2009)].
Intellectual Merit We obtained results from a simple model for potential triggering mechanisms of large earthquakes in response to a slowly increasing loading stress and an added periodic stress with amplitude F0(ω) at frequency ω. The model predicts the minimum amplitude F0min(ω) needed to observe stress-correlated triggering of large slip-events in earthquake-fault-zones [Y. Ben-Zion, Reviews of Geophys. 46, RG4006 (2008)], sheared lab-scale rocks [Lockner and Beeler, J. Geophys. Res. 104, 20133 (1999) and 108, ESE 8-1 (2003)], and sheared granular materials [H. M. Savage, C. Marone, J. Geophys. Res. 112, B02301 (2007)]. We predict F0min(ω) ~ 1/ω for small (non-zero) frequencies and decaying oscillations for F0min(ω) for large frequencies. The predictions explain and unify disparate experimental results. We also argue that correlations between small slips and periodic stresses increase as the system approaches a large slip-event/earthquake. This model prediction agrees with recent observations prior to the three large mega-thrust earthquakes in the Sumatra region [Tanaka (2010)]. These result provide new tools for earthquake- and materials-failure prediction and hazard-prevention studies, applicable to a wide variety of systems [K. A. Dahmen, Y. Ben-Zion, J. T. Uhl, Phys. Rev. Lett. 102, 175501 (2009)]. The study makes many predictions that can be tested, for example, in laboratory experiments on laboratory "faults" made of rocks and granular materials. They also provide new guidance for systematic analyses of real observations on correlations between oscillatory stresses, such as tides and seasonal stresses, and earthquake activity.
Broader Impacts This study ultimately provides new tools for earthquake prediction and hazard prevention.
THe project trained two graduate students in modern fault and rupture mechanics, seismology, and analysis of statistical signals. Through discussions within the group, 3 undergraduate research students have also been trained by this project. The project enhanced the collaboration of the University of Illinois with SCEC and the University of Southern California. Benefits to society include improved tools for earthquake prediction and hazard prevention, as well as new tools for nondestructive materials testing.
Exemplary Figure Figure 1 from 1-page Project Summary (which is Figure 3 from the technical report. Caption: Minimum (“threshold”) amplitude F0min required for detecting a correlation between the periodic driving stress and large events as a function of frequency of the oscillatory stress, on a log-log plot. The curve represents the minimum amplitude required to detect a correlation between the large earthquakes and oscillatory stresses at 99.5% confidence for n=500 recorded events: in the shaded region above the curve we detect significant correlations, while below the curve the correlations do not meet our 99.5% threshold (and are labeled ‘uncorrelated’). As expected, the minimum required amplitude decreases as more events are recorded (see prepront 1). The frequency axis is plotted in units of the small event rate λ0. The tectonic shear rate was chosen to be Γ = 0.015λ0