Multiscale characterization of fracture network in sub-seismic faults (Monte Capanne Pluton, Elba Island, Italy)

Abstract

Prediction of sub-seismic fault properties is a key factor to mitigate the uncertainties in reservoir modeling. The present study focuses on the geometry and origin of the NE-trending sub-seismic faults in Monte Capanne pluton (Elba Island, Italy), characterized by transtensive kinematics and developed in an interacting sector between two regional-scale faults. A detailed analysis of the fracture network (digitized fractures >10,000) was conducted along and across the NE-trending faults using Digital Outcrop Model (DOM). This dataset was further integrated with field mapping at a 1:200 scale of four representative sectors. Overall, our multiscale mapping identifies three different fault-related fracture sets: (i) NE-SW-trending fractures, (ii) E-W-trending fractures, and (iii) NNW-SSE-trending fractures. Statistical analysis of fracture orientation and length in DOM reveals a heterogeneous spatial distribution of deformation in the outcrop, showing an increase in fracture density and intensity (P₁₀ and P₂₁), and connectivity (connections per branch C_B) towards the northeastern region of the outcrop, where NE-trending faults are closely spaced. A comparison between DOM-based and DOM-integrated datasets reveals that the former tends to underestimate small-scale fractures due to pixel-resolution limit (truncation effect), leading to an underestimation of across-fault damage zone width and internal fracture density and intensity. However, the proportion of connected nodes (X, Y) and connectivity (C_B) from the DOM-based dataset is consistent with topological parameters from the DOM-integrated dataset. This study highlights the necessity of a multiscale approach for fracture network characterization in sub-seismic faults, combining DOM with field mapping to develop reliable templates for reservoir analysis.