Large-scale natural fracture network patterns: Insights from automated mapping in the Lilstock (Bristol Channel) limestone outcrops

Journal of Structural Geology, vol. 150, pp. 104405

Abstract

The Lilstock outcrop in the southern Bristol Channel provides exceptional exposures of several limestone beds displaying stratabound fracture networks, providing the opportunity to create a very large, complete, and ground-truthed fracture model. Here we present the result of automated fracture extraction of high-resolution photogrammetric images (0.9 cm/pixel) of the full outcrop, obtained using an unmanned aerial vehicle, to obtain a spatially extensive, full-resolution map of the complete fracture network with nearly 350,000 ground-truthed fractures. We developed graph-based functions to resolve some common issues that arise in automatic fracture tracing such as incomplete traces, incorrect topology, artificial fragmentation, and linking of fracture segments to generate geologically significant trace interpretations. The fracture networks corresponding to different regions within the outcrop are compared using several network metrics and the results indicate both inter- and intra-network (layer to layer) structural variabilities. The dataset is a valuable benchmark in the study of large-scale natural fracture networks and its extension to stochastic network generation in geomodelling. The dataset also highlights the intrinsic spatial variation in natural fracture networks that can occur even in weakly-deformed rocks over relatively short length scales of tens of metres.

Authors 5

1. Rahul Prabhakaran corresponding

   Eindhoven University of Technology · Delft University of Technology

   Affiliation as printed

   Department of Geoscience and Engineering, Delft University of Technology, Delft, the Netherlands

   Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands

2. Janos Lajos Urai Aachen Structural Geology

   RWTH Aachen University

   Affiliation as printed

   Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Aachen, Germany

3. Giovanni Bertotti

   Delft University of Technology

   Affiliation as printed

   Department of Geoscience and Engineering, Delft University of Technology, Delft, the Netherlands

4. Christopher Weismüller Aachen Neotectonics and Natural Hazards

   RWTH Aachen University

   Affiliation as printed

   Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, Germany

5. David Smeulders

   Eindhoven University of Technology

   Affiliation as printed

   Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands