Why blind thrust faults do not propagate to the Earth's surface: Numerical modeling of coseismic deformation associated with thrust‐related anticlines

Abstract

High fault‐tip stress concentrations are associated with coseismic slip on blind thrust faults and suggest that these structures should readily propagate to the Earth's surface. Seismic profiles of blind‐thrust‐related earthquakes reveal diffuse zones of aftershocks surrounding the fault tip which are attributed to inelastic deformation, such as flexural‐slip or extensional fracturing. The complex interaction between blind thrust faults and secondary structures may control the evolution of blind thrust systems. The influence of bedding‐plane slip on fault propagation is simulated with numerical models using the boundary element method. We use two parameters to estimate the tendency for thrust fault propagation, (1) the mode II stress intensity factor and (2) the maximum Coulomb stress near the fault tip. Calculations from both analyses suggest that shallow thrust faults may exhibit an increased tendency to propagate as a result of interaction with the Earth's surface and slip along bedding planes above the fault tip and a decreased tendency to propagate due to slip along bedding planes at or below the fault tip. Our results demonstrate that the magnitude and style of inelastic deformation in active fault systems control fault propagation.