The relationship among faulting, fracturing and fluids behavior is a hot research topic because the possibility to detect reliable earthquake precursors and limit the risk of induced seismicity depends on our understanding of the physics of faulting, in turn heavily affected by fluids. The project aims at understanding the role of fluids along fault systems developed in extensional and compressional settings with a multidisciplinary approach. Data will be acquired in the field (structural geology, near-surface gas geochemistry surveys, remote sensing) and by laboratory analyses (SEM, X-ray diffraction, isotope geochemistry). In addition, laboratory experiments will be performed to study the variation of permeability as a function of fracturing during slip along faults and the mechanical properties of fault damage zones. Numerical modelling will be performed to investigate the role of fluids in fault mechanics and the role of fault rocks in the determination of fluids pathways.
The following research objectives will be pursued:
1) understanding the origin of fluids permeating fault zones during their activity and exhumation;
2) understanding the role of fluids at coseismic stages;
3) understanding the factors that control the distribution of fractures in fault damage zones;
4) understanding the control of deformation on fluid flow and pressure.
5) understanding the mechanical behavior of fault damage zones.
We foresee the following innovative results:
1) we will develop a model by integrating the evolution of fault zone structure with the nature and role of geofluids from km down to the nano-scale for extensional and compressional settings;
2) we will build a model for the distribution of fractures in fault zones and their control on fluid flow;
3) we will characterize the elastic moduli of damage zone rocks of carbonate-bearing faults;
4) ¿we will quantify the role of fluids in fault mechanics and the role of fault rocks in the determination of fluids pathways.
The main goal of this proposal is to develop a coherent understanding of the role of fluids and fluid pressure in the physics of earthquakes. To do this, we propose a multiscale and multidisciplinary study based on field geology, structural and geochemical laboratory analyses, rock deformation experiments and numerical models. The multiscale and multidisciplinary nature of our approach is innovative and will add valuable information to the state of the art.
We foresee the following innovative results:
1) Based on our previous and ongoing research dedicated to the study of fault zone structure of carbonate-bearing faults (e.g. Collettini et al., 2014) and fluids-rocks interaction in fault zones (Smeraglia et al, 2017) we will develop a model integrating the evolution of the fault zone structure with the nature and role of geofluids from km down to the nano-scale for extensional and compressional environments. This model will be based on fieldwork combined with microstructural (optical microscopy, scanning electron microscopy field emission, cathodoluminescence) and geochemical (isotopic analyses) studies of the fault rocks and veins. This will allow us to constrain fault rock evolution (from the protolith to the mature shear zone), fluid-rock interaction and to characterize the main deformation mechanisms.
2) Based on field an remote sensing detailed structural analyses (Lato et al, 2009; Sturzenegger and Stead, 2009) and near-surface gas geochemistry surveys we will build a model for the distribution of fractures and their control on fluid flow in the Tre Monti fault damage zone.
3) We will characterize the elastic moduli of carbonate-bearing faults under different values of fluid pressure and damage, induced by loading/unloading stress cycles. The elastic moduli will be measured during the experiments and also inferred by body wave speed analysis (e.g. Trippetta et al., 2013). During the experiments we will also measure the permeability of the rocks. Experiments will be performed using the BRAVA rock deformation apparatus (Collettini et al., 2014) on cylindrical samples with dimensions of both 38 and 100 mm of diameter.
4) ¿We will quantify the role of fluids in fault mechanics and the role of fault rocks in the determination of fluids pathways with finite elements models using COMSOL Multiphysics software (http://www.comsol.com/). Based on previous experience on numerical modelling (Doglioni et al., 2013; Carminati and Vadacca, 2010) rock mechanics (plane strain or plane stress modules in COMSOL) and fluid behavior (Darcy's module) will be solved contemporaneously and a poroelastic rheology will be adopted. Mechanical parameters, porosity and permeability of rocks will be constrained by field and laboratory analyses. Fault geometries similar to those constrained by our geological and remote sensing data will be modelled.
5) We will define the main fault zones by mineralogical, petrographic, petrological and structural analyses. Damage zones and gouges will be studied by fluid inclusion microthermometry and petrography of vein systems in order to provide information on temperature and fluid composition during deformation and by X-ray diffraction analysis for quantifying the maximum depth at which deformation occurred. Furthermore, mineralogical variations among different portions of the fault structure will allow us to distinguish neoformed minerals derived fluid/rock interaction from those minerals derived by fault comminution.
Collettini et al, 2014. BRAVA: a novel Brittle Rock deformAtion Versatile Apparatus. International Journal of Rock Mechanics and Mining Sciences, 66, 114-123
Carminati & Vadacca, 2D and 3D numerical simulations of the stress field at the thrust-front of the Northern Apennines, Italy, Journal of Geophysical Research, 115, B12425, doi:10.1029/2010JB007870, 2010
Doglioni, Barba, Carminati, Riguzzi, 2013. Fault on-off versus coseismic fluids reaction, Geoscience frontiers, 10.1016/j.gsf.2013.08.004
Smeraglia, Billi, Carminati, Cavallo, Di Toro, Spagnuolo, Zorzi, F, 2017. Ultra-thin clay layers facilitate seismic slip in carbonate faults. Scientific Reports, 7, 664
Lato et al, 2009 Optimization of LiDAR scanning and processing for automated structural evaluation of discontinuities in rockmasses. Int J Rock Mech Min Sci 46:194¿199. doi:10.1016/j.ijrmms.2008.04.007
Sturzenegger & Stead, 2009. Quantifying discontinuity orientation and persistence on high mountain rock slopes and large landslides using terrestrial remote sensing techniques. Nat Hazards Earth Syst Sci 9,267¿287
Trippetta, Collettini, Meredith, Vinciguerra, 2013. Evolution of the elastic moduli of seismogenic Triassic Evaporites subjected to cyclic stressing. Tectonophysics, 592, 67-79.