Earthquakes represent a fundamentally challenging scientific problem. In the last decade the new geophysical discoveries have greatly improved our knowledge on how faults accommodate slip and on their ability to produce earthquakes. Geophysical and geodetic observations, source modeling and experiments suggest that faults are heterogeneous in their physical properties and temporal behavior, leading to variations and complexities in slip styles, friction, earthquake recurrence intervals and involved physical processes.
The aim of this project is to study the effect of fault rock (in terms of its fabric) and strain localization in controlling traction evolution and slip velocity time histories during laboratory earthquakes. We will use a double-direct biaxial shear apparatus and different fault gouges, including heterogeneous minerals mixture as a proxy for real fault rocks, to study slip events at the laboratory scale.
Measuring fine details of fault slip velocity time history, volumetric deformation and friction during many seismic cycles, coupled with an analysis of the microstructures, we want to get inferences on the physical processes at play.
The slip velocity function contains the dynamic information needed to characterize the evolution of stress during breakdown process and it is usually imposed a-priori during earthquakes kinematic modeling on natural faults due to the limited resolution of recorded data. With our project we want to study the spontaneous slip velocity function recorded during laboratory events and to relate its temporal evolution with shear fabric. Moreover, with the use of different fault gauges we want to get inferences on how the energy is differently absorbed on the slipping surfaces with significant insights for understanding of earthquake process.
Finally, the multidisciplinary geophysical team recently assembled in Sapienza will be a perfect environment to train PhD and Post-docs researchers interested in earthquake mechanics.
Earthquakes arise as frictional instabilities along tectonic faults, producing seismic ruptures and in some cases catastrophic natural disasters. Recent studies show that fault slip can occur not only seismically or aseismically, via stable creep, but also through slow processes such as slow-slip events, low-frequency events and episodic tremor that in some cases precede large and destructive earthquakes (Hirose and Obara, 2005; Schwartz and Rokosky, 2007; Rubinstein et al., 2010; Beroza and Ide, 2011).
From the literature it has been demonstrated that faults capable of hosting a large spectrum of slip behavior are represented by structures that have lithological, mechanical and frictional heterogeneity in space (Barnes et al., 2020).
Laboratory studies of stick-slip frictional instability have allowed the understanding of earthquake mechanics (e.g., Scholz, 2002). Recently, laboratory observations have also begun to illuminate the mechanics of slow slip and oscillatory stable sliding (e.g., Kaproth and Marone, 2013; Ikari et al., 2013, 2015; Leeman et al., 2016; Scuderi et al., 2016, Tinti et al., 2016). However these studies have been done mainly for a single mineralogic phase.
Our proposed work will be the first systematic study of the breakdown processes during slip instability generated spontaneously in lab by using geo-materials with heterogeneous mineralogical composition, such as mixtures of anhydrites - dolomites and serpentinites. In order to shed light on the mechanical processes that can be at the origin of the frictional instabilities during laboratory slip events, we will pay attention to the relation among many parameters: the slip localization, the fault structure and the inferred slip weakening behavior and slip velocity time history.
To further understand the different response and the dynamic processes occurring during the co-seismic breakdown stage, we will compute the mechanical work absorbed during frictional instabilities associated with slip events. In particular, we will infer the breakdown work, defined as the excess of work over the traction level having minimum magnitude (¿min) achieved during slip, that is a measure of absorbed energy during the coseismic phase.
The planned rock deformation experiments, in general will contribute to a comprehensive characterization of the breakdown processes with strong impact for all the physical models aimed at the characterization of earthquake nucleation.
By using BRAVA rock deformation apparatus (Collettini et al., 2014) and possibly the BRAVA 2.0 apparatus developed at DST within Progetto Dipartimento di Eccellenza we will be able to reproduce stability conditions that will allow spontaneous fault instabilities also for heterogeneous rock, opening the door for a significant advancement of knowledge with direct implications for the mechanics of earthquakes.
References
Barnes et al., 2020,Sci. Adv. 6 : eaay3314
Beroza and Ide, 2011, Annu. Rev. Earth Planet. Sci., 39, 271-296
Collettini et al., 2014; Int. J. Rock Mech. Min. Sci., 66, 114-123
Hirose and Obara, 2005;Earth Planets Space, 57, 961-972.
Ikari et al., 2013, Nat. Geosci., 6, 468-472
Ikari et al., 2015;Nat. Geosci., 1-6,
Kaproth and Marone, 2013;Science, 341(6151), 1229-1232
Leeman et al., 2016; Nat. Commun., 7, 11104
Rubinstein et al., 2010; New Frontiers in Integrated Solid Earth Sciences, pp. 287-314
Schwartz and Rokosky, 2007; Rev. Geophys., 45, RG3004
Scholz, 2002;Cambridge University Press, 504 p.,
Scuderi et al., 2016; Nature Geoscience, DOI: 10.1038/NGEO2775
Tinti et al., 2016, J. Geophys. Res. Solid Earth, 121