Abstract - The Vallès-Penedès Fault is a Neogene normal fault marked by the presence of two established geothermal
systems at La Garriga-Samalús and Caldes de Montbuí, within the Catalan Coastal Ranges (NE Spain). The
analysis and collation of existing and new geological and geophysical datasets provide the basis for the development
of an improved conceptual model that explains the presence and localization of hot geothermal fluid
systems at relatively shallow depths (e.g., 60 oC at surface and 90 oC at 1 km). Geothermal flow is concentrated
within Paleozoic granodiorites of the immediate footwall of the V-P fault, host rocks that are susceptible to faultrelated
fracturing, and the generation of both extension and hybrid fracture systems in association with active
fault displacements. Flow localization is enhanced further by the presence of fault-related structural complexities,
with both systems marked by 300 m wide steps in the main fault trace. These are attributed to relay
development and breaching characterizing host rocks by high fracture intensities and fault rock development on
a fault that locally has a vertical displacement of over 1.5 km. Accentuated fracturing and deformation are
consistent with strain localization predicted by existing models for the development of fault zones along normal
faults. The plumbing of the geothermal systems is attributed to up-fault flow in combination with lateral flow
controlled by the intersection of the V-P fault with a low-angled Paleogene thrust defining the base of the hostrock
granodiorites, with the geothermal systems localized at the distal end of the thrust. Sustained geothermal
flow is attributed to groundwater flow circulation associated with seismic pumping and valving of warmer and
deeper fluids, and the ingress of groundwater along faults and within fractured basement rocks.
Geothermics, 116, 102855. doi: https://doi.org/10.1016/j.geothermics.2023.102855, 2023.