Historical shear deformation of rock fractures derived from digital outcrop models and its implications on the development of fracture systems

TL;DR

This paper introduces a quantitative method using digital outcrop models to derive the historical shear deformation of rock fractures, overcoming subjectivity in traditional visual interpretation and aiding in understanding fracture system development.

Contribution

A novel quantitative approach that models and estimates historical shear deformations from digital outcrop data, integrating effects of fault features on shear strength.

Findings

Method successfully tested on idealized and real fracture surfaces.

Application reveals deformation history and fracture development patterns.

Preexisting fractures influence new fracture distribution and mode.

Abstract

The initiation and development of fractures in rocks is the key part of many problems from academic to industrial, such as faulting, folding, rock mass engineering, reservoir characterization, etc. Conventional ways of evaluating the fracture historical deformations depend on the geologists' visual interpretation of indicating structures such as fault striations, fault steps, plumose structures, etc. on the fracture surface produced by previous deformations, and hence suffer from problems like subjectivity and the absence of obvious indicating structures. In this study, we propose a quantitative method to derive historical shear deformations of rock fractures from digital outcrop models (DOMs) based on the analysis of effects of fault striations and fault steps on the shear strength parameter of the fracture surface. A theoretical model that combines effects of fault striations, fault steps and isotropic base shear strength is fitted to the shear strength parameter. The amount of fault striations and fault steps and their occurrences are estimated, and the historical shear deformations can be inferred. The validity and the effectiveness of the proposed method was proved by testing it on a constructed fracture surface with idealized striations and a fracture surface with clear fault steps. The application of this method on an example outcrop shows an intuitive idea of how the rock mass was deformed and that the distribution, occurrence and mode of new fractures are strictly controlled by preexisting fractures, and hence emphasizes the importance of preexisting fractures in modeling the development of fracture systems.