Periodic Reporting for period 1 - FRICTION (Fluid-Rock InteraCTION at hydrothermal conditions during the seismic cycle)
Periodo di rendicontazione: 2020-08-01 al 2022-07-31
Earthquakes, sometimes human-induced, cause about 50,000 casualties per year and billions of euros in damage. However, the probabilistic forecasting of earthquakes is challenged by our poor knowledge of earthquake physics and chemistry. In fact, the most damaging earthquakes are the result of ruptures nucleating and propagating in the Earth’s crust along faults often impregnated by water-rich hot fluids ('hydrothermal fluids'). The poorly understood chemical and physical interaction between these fluids and the fault rock materials controls the early stages of earthquake nucleation. The EU-funded FRICTION project focuses on the dynamic interaction between hydrothermal fluids and fault zones in the continental crust. The study of ancient seismic faults, now exposed at the surface, and dedicated novel experiments reproducing these particular hydrothermal conditions will help to quantify the mechanical behavior of faults in the presence of fluids at seismogenic depths, also for the safe exploitation of deep-seated reservoirs for energy purposes (geothermal fields, etc.).
During the duration of the FRICTION project I carried out field geological studies, novel rock deformation experiments, and Petrographical, Mechanical, Chemical, and Microstructural Analyses.
The field geological studies included the production of high-resolution structural maps quantifying the spatial distribution of the distinct deformation stages and their characteristic hydrothermal signature. The fieldwork allowed me to describe the first pseudotachylytes recognized in the Atacama Fault System (AFS) in Northern Chile, characterized by the presence of amygdales both, spatially and temporally associated with foliated hydrothermally altered fault-core rocks in a strong fluid-rock interaction environment. Also to constrain the formation of pseudotachylytes (by long time thought to be unique to certain water-deficient seismogenic environments) to hydrothermal fluid-rich environments. The details of these findings are detailed in Gomila et al., GGG (2021).
Prior to the realization of the rock deformation experiments, I successfully installed, implemented and started-up a new hydrothermal vessel unique of its type in Europe (with only a couple more around the world), which allowed me to perform novel deformation experiments in rotary configuration (shear velocity of 10 µm/s) under hydrothermal conditions (temperature of 300°C and fluid pressure of 25 MPa). The analyses of the experimental products (both mechanical data and the “post mortem” microstructures of experimental samples) showed a change in fault healing rates from positive to negative, which was a mayor discovery of this project, with potential implications in our understanding on earthquakes nucleation and recurrency. These findings would suggest that under hydrothermal conditions, total shear displacement and duration of the fluid-rock interaction enhance mineral reactions that promote negative healing rates in faults during the seismic cycle. This would imply that during the life-span of an evolving fault, as it matures, it would be possible to (1) lower the fault yield strength due to and increasing fluid-rock interaction, henceforth (2) increase the recurrence but decrease the intensity of the seismic activity.
Part of the findings of this project have been disseminated in presentations at different conferences (as posters and as an invited speaker), in 2 open-access publications in ISI journals and publication of data in open-access repositories, in addition to several outreach activities.
The field geological studies included the production of high-resolution structural maps quantifying the spatial distribution of the distinct deformation stages and their characteristic hydrothermal signature. The fieldwork allowed me to describe the first pseudotachylytes recognized in the Atacama Fault System (AFS) in Northern Chile, characterized by the presence of amygdales both, spatially and temporally associated with foliated hydrothermally altered fault-core rocks in a strong fluid-rock interaction environment. Also to constrain the formation of pseudotachylytes (by long time thought to be unique to certain water-deficient seismogenic environments) to hydrothermal fluid-rich environments. The details of these findings are detailed in Gomila et al., GGG (2021).
Prior to the realization of the rock deformation experiments, I successfully installed, implemented and started-up a new hydrothermal vessel unique of its type in Europe (with only a couple more around the world), which allowed me to perform novel deformation experiments in rotary configuration (shear velocity of 10 µm/s) under hydrothermal conditions (temperature of 300°C and fluid pressure of 25 MPa). The analyses of the experimental products (both mechanical data and the “post mortem” microstructures of experimental samples) showed a change in fault healing rates from positive to negative, which was a mayor discovery of this project, with potential implications in our understanding on earthquakes nucleation and recurrency. These findings would suggest that under hydrothermal conditions, total shear displacement and duration of the fluid-rock interaction enhance mineral reactions that promote negative healing rates in faults during the seismic cycle. This would imply that during the life-span of an evolving fault, as it matures, it would be possible to (1) lower the fault yield strength due to and increasing fluid-rock interaction, henceforth (2) increase the recurrence but decrease the intensity of the seismic activity.
Part of the findings of this project have been disseminated in presentations at different conferences (as posters and as an invited speaker), in 2 open-access publications in ISI journals and publication of data in open-access repositories, in addition to several outreach activities.
The project FRICTION enabled me to collect novel information about the spatial extent and the ambient conditions of fluid-rock interaction associated with the seismic cycle in fault zones in the crystalline basement with unprecedent detail. In particular, how pseudotachylytes (which represent the “scar” of ancient earthquakes), could be temporary and spatially associated with hydrothermal fluids, changing our paradigm that these kind of rocks could only be formed in a fluid-deficient ambient.
The rock deformation experiments allowed me to install a new Hydrothermal Vessel unique in Europe (with only a few others around the globe) that would allow us to increase our knowledge on deformation processes during the seismic cycle under geothermal conditions, which are the conditions that natural and human-induced earthquakes occur.
The rock deformation experiments allowed me to install a new Hydrothermal Vessel unique in Europe (with only a few others around the globe) that would allow us to increase our knowledge on deformation processes during the seismic cycle under geothermal conditions, which are the conditions that natural and human-induced earthquakes occur.