Slip on geological faults can be triggered by remote earthquakes up to a thousand kilometers 
away. This phenomenon is known as dynamic triggering and may generate new earthquakes. Pore 
fluid pressure in preexisting faults appears to be an important agent in the triggering. It 
is known that pore pressure elevation may lead to fault instability, however, the mechanism 
by which pore pressure rises and brings faults to their failure during seismic shaking is 
poorly understood. Here, we propose to develop a physical model of fault stability based on 
mechanics of the coupled granular matter + fluid (water) system. Deformation of the granular 
skeleton due to seismic waves is coupled to evolution of fluid pressure and, vice versa, fluid 
exerts a pressure force on the grains. The coupled dynamics of pressure and granular deformation 
will be solved numerically using the discrete-element and finite-element methods. Results will 
provide theory for pore-fluid effects on weakening of gauge zones and implications for 
seismic-hazard assessment.