Earthquake nucleation mechanisms and periodic loading: Models, Experiments, and Observations

The project has two main goals: (a) Improve the understanding of how earthquakes are nucleated ¬ with specific focus on seismic response to periodic stresses (such as tidal or seasonal variations) (b) Use the results of (a) to infer on the possible existence of precursory activity before large earthquakes. A number of mechanisms have been proposed for the nucleation of earthquakes, including frictional nucleation (Dieterich 1987) and fracture (Lockner 1999, Beeler 2003). We study the relation between the observed rates of triggered seismicity, the period and amplitude of cyclic loadings and whether the observed seismic activity in response to periodic stresses can be used to identify the correct nucleation mechanism (or combination of mechanisms). A generalized version of the Ben-Zion and Rice model for disordered fault zones and results from related recent studies on dislocation dynamics and magnetization avalanches in slowly magnetized materials are used in the analysis (Ben-Zion et al. 2010; Dahmen et al. 2009). The analysis makes predictions for the statistics of macroscopic failure events of sheared materials in the presence of added cyclic loading, as a function of the period, amplitude, and noise in the system. The employed tools include analytical methods from statistical physics, the theory of phase transitions, and numerical simulations. The results will be compared to laboratory experiments and observations. References: Beeler, N.M., D.A. Lockner (2003). Why earthquakes correlate weakly with the solid Earth tides: effects of periodic stress on the rate and probability of earthquake occurrence. J. Geophys. Res.-Solid Earth 108, 2391-2407. Ben-Zion, Y. (2008). Collective Behavior of Earthquakes and Faults: Continuum-Discrete Transitions, Evolutionary Changes and Corresponding Dynamic Regimes, Rev. Geophysics, 46, RG4006, doi:10.1029/2008RG000260. Ben-Zion, Y., Dahmen, K. A. and J. T. Uhl (2010). A unifying phase diagram for the dynamics of sheared solids and granular materials, Pure Appl. Geophys., in review, 2010. Dahmen, K.A., Y. Ben-Zion, and J.T. Uhl (2009). A micromechanical model for the deformation in solids with universal predictions for stress-strain curves and slip avalanches, Phys. Rev. Lett. 102, 175501/1-4. Dahmen , K.A. and Y. Ben-Zion (2009). The physics of jerky motion in slowly driven magnetic and earthquake fault systems. Encyclopedia of Complexity and System Science, R. Meyers (Eds.), Vol. 5, 5021-5037, Springer. Dieterich, J. H. (1987). Nucleation and triggering of earthquake slip: effect of periodic stresses, Tectonophysics 144, 127-139. Lockner, David A. and Nick M. Beeler (1999). Premonitory slip and tidal triggering of earthquakes, J. Geophys. Res. 104, 20,133-20,151.