EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geological imaging of a crustal-scale seismogenic source in the continental crust (Bolfin Fault Zone, Atacama Fault System, Chile)

Simone Masoch1, Michele Fondriest2, Rodrigo Gomila1, Erik Jensen3, Giulia Magnarini4, Javier Espinosa5, Karin Hofer5, Tom Mitchell4, José Cembrano5,6, Giorgio Pennacchioni1, and Giulio Di Toro1,7
Simone Masoch et al.
  • 1Università degli Studi di Padova, Department of Geosciences, Padova, Italy (
  • 2Institut de Sciences de la Terre (ISTerre), Université Grenoble-Alpes, France
  • 3CIGIDEN, Santiago, Chile
  • 4Department of Earth Sciences, University College London, London, United Kingdom
  • 5Departamento de Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Santiago, Chile
  • 6Andean Geothermal Center of Excellence (CEGA, FONDAP-CONICYT), Santiago, Chile
  • 7Sezione di Tettonofisica e Sismologia, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy

Fault zone architecture controls, for instance, the nucleation, propagation and arrest of individual seismic ruptures, the moment magnitude of the mainshocks and the evolution in space and time of foreshock and aftershock seismic sequences. Nevertheless, the architecture of crustal-scale seismogenic sources is still poorly known. Here, we examine the architecture of the >40-km-long, Mesozoic seismogenic Bolfin Fault Zone (BFZ) of the Atacama Fault System (Northern Chile). The exceptionally well-exposed BFZ cuts through plutonic rocks of the Coastal Cordillera and was seismically active at 5-7 km depth and ≤ 300 °C in a fluid-rich environment. The BFZ includes multiple fault core strands consisting of chlorite-rich cataclasites-ultracataclasites and pseudotachylytes, surrounded by chlorite-rich protobreccias to protocataclasites over a zone as wide as 75 m. These cataclastic units are associated with a damage zone, up to 150-m-thick, which comprises strongly altered and brecciated rock volumes, and with clusters of epidote-rich fault-vein networks located at the linkage of the BFZ with other faults. The architecture of the BFZ is the result of fault core widening by cyclic co-seismic frictional melting and post-to-inter-seismic fault healing due to hydrothermal (chlorite + epidote ± K-feldspar) mineral precipitation plus pervasive, possibly associated with mainshocks and aftershocks, damaging of the surrounding rocks. Additionally, we interpret the epidote-rich fault-vein networks as an exhumed seismic source of fluid-driven earthquake swarm-type sequences in agreement with seismological observations of presently active magmatic and hydrothermal regions. 

How to cite: Masoch, S., Fondriest, M., Gomila, R., Jensen, E., Magnarini, G., Espinosa, J., Hofer, K., Mitchell, T., Cembrano, J., Pennacchioni, G., and Di Toro, G.: Geological imaging of a crustal-scale seismogenic source in the continental crust (Bolfin Fault Zone, Atacama Fault System, Chile), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1926,, 2022.


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