CAREER: Multiscale Mechanics of Fluid Infiltrated Fault Zones- An Integrated Research and Education Plan

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Earthquakes and landslides are among the costliest natural hazards on earth with hundreds to thousands of lives and millions to billions of dollars lost every year. The dynamical instabilities responsible for the onset and ensuing propagation of these events are linked to fundamental physics- friction, fracture, heating, and compaction- of fluid filled granular materials and rocks in the subsurface subjected to extreme geophysical conditions. Events like Tohoku and Chi-Chi earthquakes have conclusively shown that seismic hazard critically depends on the underlying fault physics including spatial heterogeneity in hydraulic properties and pore pressure generation. Advancing frontiers in micromechanical modeling of deformation and failure in fluid infiltrated geological materials and computational modeling of earthquake ruptures in heterogeneous fault zones under realistic conditions are the objective of this study. This provides a pathway for predictive modeling of these critical phenomena and development of better-informed seismic hazard models. Blending perspectives from nonlinear mechanics, statistical physics, numerical methods, and seismology provides a wide range of scientific and educational opportunities, with impact on natural hazards policy and preparedness as well as technical training of the future workforce. Central to this project is building bridges between the geophysics and mechanics communities using a set of well-coordinated activities including workshops, conferences, and social media platforms which will lead to cross-pollination of ideas and nurturing a new class of scientists and engineers with strong interdisciplinary training. Professional mentoring of undergraduate and graduate students, especially from under represented communities is a critical component of the proposed educational plan. The objective of this CAREER project is to develop a plan to advance frontiers in earthquake source physics using an interdisciplinary research and an interdisciplinary educational approach. Despite the potentially dominating rule of pore fluid pressure variations in earthquake source nucleation and propagation, the multiscale mechanics of fluid infiltrated fault zones is not yet fully understood using the current modeling and experimental techniques. This study will address this critical challenge by integrating novel theoretical tools from material science, mechanics and computation and by developing an educational platform that nurtures a class of students and researchers who are intrinsically motivated in working on problems bridging geoscience and engineering. The research component of this CAREER project aims (1) to theoretically investigate the mechanical response of fluid saturated gouge layers sheared in the presence and absence of mechanical vibrations using a novel physics-based continuum viscoplasticity model based on Shear Transformation Zone theory. The model resolves complex feedback mechanisms between gouge compaction, dilation, pore pressure changes and shear heating leading to identification and discovery of complex strength evolution histories in fault zones connected with nucleation and propagation of nonplanar shear bands and stick-slip instabilities, and (2) to couple this new fault zone model with the elastic bulk to investigate earthquake rupture propagation in complex settings using a new numerical technique that couples spectral boundary integral and finite element methods. The theoretical models will be validated against a variety of laboratory measurements and seismic observations available in the literature. The educational component of this project aims (1) to facilitate and enrich interactions between material scientists, rock mechanicians and seismologists, through organization of interdisciplinary workshops and conference symposia, as well as leveraging social media platforms for disseminating interdisciplinary research products, and (2) to inspire students, especially minority and female students, to learn and participate in interdisciplinary research through various outreach activities, curricular material innovation, and REUs engagement.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.