The influence of fault geometrical complexity on the precursory process of geological disasters

Abstract

Previous studies about natural disasters proved the crucial influence of fault geometrical complexity. The laboratory tests were conducted to investigate its effect, and the fault misalignment ratio was used to quantify fault geometrical complexity. Samples with different fault misalignment ratios were compressed under uniaxial and triaxial conditions, with a distributed optical fiber sensor (DOFS) being applied to obtain full-field deformation across the sample surface. The entire process of deformation localization was quantified by the Gini coefficient. Moreover, the acoustic emission (AE) was used to capture fracture signals during the entire process. The difference in failure processes, influenced by various fault geometries, was compared based on mechanical and deformation characteristics. Results show that fault networks with simple geometrical characteristics facilitate strain delocalization with slow and small stress drops, which may originate from slow fault slip. However, strain localization dominates the entire deformation process with sudden and larger stress drops for fault networks with complex geometry. The analysis of deformation localization and stress drops indicates that a crucial fault misalignment ratio, significantly changing the failure mechanism, may appear between 0.2 and 0.4. The CT images show that crack propagation controls the deformation process, and the potential mechanism was explored to explain this difference.

Keywords

Fault geometry / Mechanical response / Strain localization / Optical fiber / Crack distribution

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