Rock fractures play a fundamental role in fluid migration through the crust, rendering them important in geoenergy applications. Although often modelled as smooth parallel plates, fracture surfaces are rough, and roughness impacts transport properties. Despite their importance, there remains a paucity of data related to what controls fracture roughness and, consequently, how this affects fluid flow. Here, we examine how fracture orientation affects fracture roughness in Nash Point Shale, using laboratory-and synchrotron-based µ-CT, and optical microscopy methods, and consequently how fracture orientation and roughness affect fluid flow through a series of core flooding experiments. We show that there is a strong correlation between fracture orientation, fracture roughness and surface area, for fractures between the Short-transverse and Arrester orientations. Fractures in the Divider orientation have both a larger surface area and higher roughness than fractures in all other orientations, which we relate to fundamental differences in the fracture mechanics in this orientation. We also measured the permeability of samples containing mated fractures of different orientations to bedding but discovered no systematic differences between them.

In an active volcanic arc, magmatically sourced fluids are channeled through the brittle crust by structural features. This interaction is observed in the Andean volcanic mountain belt, where volcanoes, geothermal springs and the locations of major mineral deposits coincide with NNE-striking, convergent margin-parallel faults and margin-oblique, NW/SE-striking Andean Transverse Faults (ATF). The Tinguiririca and Planchón-Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as both volcanic complexes and their spatially associated thermal springs show strike alignment to the outcropping NNE oriented El Fierro Thrust Fault System. This study aims to constrain the 3D architecture of this fault system and its interaction with volcanically sourced hydrothermal fluids from a combined magnetotelluric (MT) and seismicity survey. The 3D conductivity model and seismic hypocenter locations show correlations between strong conductivity contrasts and seismic clusters in the top 10km of the crust. This includes a distinct WNW-striking seismogenic feature which has characteristics of the ATF domains. As the surveyed region is characterized by high heat flow regimes, volcanic activity and hydrothermal systems related to the volcanic arc, the conductivity contrast suggests that magmatically derived fluids meet an impenetrable barrier, most likely the sealed core of the fault. The resulting increase in hydrostatic fluid pressure facilitates seismic activity on this WNW oriented structure. These results provides the first observation of the mechanism behind the reactivation and seismogenesis of ATF. The study also uncovers the role of the ATF the compartmentalization of magmatic-derived fluids that accumulate to form hydrothermal reservoirs in the SVZ.