The knowledge of fault zone structure and mechanics is essential to better understand the physics of earthquakes and for a better assessment of seismic risk. Two main elements can be individuated within fault zones: A fault core, where most of the slip is accommodated, made up of fine-grained rocks produced by frictional processes, surrounded by a damage zone where the host rock is intensely fractured. The capability for a fault to host earthquakes depends both on frictional properties of the fault and on elastic properties of the rock surrounding the fault. In particular, the rate of decrease in friction with slip on a fault (kc) must be higher than the elastic stiffness of the surrounding rocks (k). The vast majority of fault mechanics studies performed in the laboratory focuses on the frictional properties of the fault core although the fracturing in the damage zone may alter the elastic properties of the host-rock that surrounds the fault. The aim of the present research project is to characterize the fault mechanics by considering both the frictional properties of the fault core and the elastic properties of the damage zone. This aim will be pursued integrating detailed geological structural studies on exhumed fault zones in the Apennines with rock mechanics experiments performed on natural samples coming from both the fault core and the damage zone. Outcomes expected from this research will allow to better understand the link between fault structure and mechanics and, consequently, to better interpret in a mechanical sense the outcrops of exhumed faults, pictures of faults coming from detailed seismic reflection studies and from high-resolution aftershock relocation.
This research will represent one of the first studies on fault mechanics accounting for the whole fault zone structure (i.e., fault core + damage zone). The research activities will be based on the integration of detailed structural characterization of beautifully exposed natural fault zones with experiments performed on a state-of-the-art rock mechanics apparatus.
For this study I will leverage on my experience with detailed characterization of fault damage zones (Mercuri et al., 2020a, 2020b), and with the BRAVA apparatus (Mercuri et al., 2018).
Outcomes expected from this research will improve our understanding of fault mechanics and will allow a better assessment of seismic risk. In particular, rock mechanics experiments, designed to fit structural geology observations made on natural outcrops of fault zones will allow to better understand the link between fault structure and mechanics and, consequently, to better interpret in a mechanical key the outcrops of exhumed faults, or pictures of faults coming from detailed seismic reflection studies and high-resolution aftershock relocation.
References:
Mercuri, M., Scuderi, M.M., Tesei, T., Carminati, E., Collettini, C., 2018. Strength evolution of simulated carbonate-bearing faults: The role of normal stress and slip velocity. Journal of Structural Geology 109, 1¿9.
Mercuri, M., McCaffrey, K.J.W., Smeraglia, L., Mazzanti, P., Collettini, C., Carminati, E., 2020a. Complex geometry and kinematics of subsidiary faults within a carbonate-hosted relay ramp. Journal of Structural Geology 130, 103915.
Mercuri, M., Carminati, E., Tartarello, M.C., Brandano, M., Mazzanti, P., Brunetti, A., McCaffrey, K.J.W., Collettini, C., 2020b. Lithological and structural control on fracture frequency distribution within a carbonate-hosted relay ramp. Journal of Structural Geology 104085.