Density, length and connectivity of fractures in a fault zone: the case of the San Miguel de Allende fault

Abstract

We analyze the number, length, distribution, and fracture connectivity associated with the San Miguel de Allende fault (FSMA). For this analysis, we estimated parameters such as density, box dimension, fragmentation dimension, and connectivity. Our results show that within the damage zone of the FSMA, three fracture generation events occurred. The first (D1) is associated with the Late Cretaceous-Paleogene orogenic event and formed subvertical calcite veins with NE-SW and NW-SE orientations. The other two events (D2 and D3) are related to the Cenozoic activity of the FSMA in the Oligocene-Miocene, generating subvertical open fractures, and gypsum and amorphous quartz veins, with NE-SW, NW-SE, and N-S preferential orientations. Fractures in the damage zone are mainly extensional, hybrid, and shear. They have an average density of 3000 fractures/m², a box dimension between 1.31 and 1.84, and a fragmentation dimension between 1.86 and 3.81. Its connectivity exceeds the threshold of 2 connections per fracture (C=2) in the ternary diagram of nodes I, Y, and X, which suggests good connectivity between the fractures, while the parameter F_m, which characterizes the architecture of the fault zone and permeability, shows that the damage zone of the FSM acts as a conduit. Based on our results, we suggest that fracture reactivation is an effective mechanism for strain accommodation and increases the number, connectivity, and permeability of fractures in the damage zones.