This study of ontology and knowledgebase of fractures and faults facilitates a sound communication and understanding in the subject domain. Fractures and faults are the most ubiquitous structures in the upper crust and they can impact many societal and industrial activities including oil and gas exploration and production, aquifer management, CO₂ sequestration, waste isolation, the stabilization of engineering structures, and assessing natural hazards. Ontologies formally represent concepts in a logic way. They can be used as a vocabulary that represent and communicate knowledge, to define relationships between the terms of the vocabulary, and to encode skeletal knowledge that can be used by a computer.

The ontology of fractures and faults makes explicit specifications about fractures and faults, their properties, and the deformation mechanisms which lead to their formation and evolution. It emphasizes the relationships among concepts, such as the factors that influence the mechanism(s) responsible for the formation and evolution of specific fractures and faults. The Web Ontology Language description logic (OWL-DL) is used to make ontological statements.

The ontology consists of about 300 concepts and 50 relationships, referencing about 150 articles or textbooks. The concepts can be divided into three major categories, Geological Structures, Deformation Mechanisms, and Properties and Factors. The relationships have five major areas: geometry of structures, constitution of structures and components, factors effecting deformation mechanisms, factors effecting structure's geometry, and fluid flow properties affected by geological structures.

Two applications of the ontology are demonstrated. First, it is used in query expansion on queries about fault permeability over two search engines. The results with the expansion show increased precision compared to the query only paradigm. Second, with the addition of comments in human language and supporting materials, the ontology is transformed into a knowledgebase, which consists of a series of web pages. This knowledgebase is to provide users knowledge and information related to fractures and faults for education and training purposes.