The minimum depth of fault failure in compressional environments

Abstract

The absence of very shallow seismicity in thrust faults could be due to either a layered pore pressure/depth profile or to heterogeneous lithology of the crust. Poroelasticity equations were solved by the finite element discretization of a two‐dimensional plane strain cross‐section simulating a thrust environment. Although the modeled faults are actively compacting during thrusting, our numerical results show that the pore pressure accumulation in the basement is faster than in the fault zone and therefore the fluid flow is directed into the fault. The combination of heterogeneous rheology, with the existence of hydrostatic fluid, retards failure near the land surface. A layered pore pressure/depth profile, where the pore pressure is hydrostatic in the sediments and near lithostatic in the basement, magnifies this result and failure occurs faster. In fact, with this pore pressure/depth profile, failure is reached at the same depth regardless of the crustal structure we assume.