Most faults and rockslides exhibit time-dependent deformation known as brittle creep which has been characterized through laboratory experiments in the literature on several lithologies. These experiments highlighted the strong influence of lithology on fault creep behaviour as well as on rates of geomorphic processes in landscape evolution. Creep processes in rock masses have been recently demonstrated to be very important factors for the development of instabilities at slope scale over a long- to very-long-time interval.
The aim of this project is to characterize the creep behaviour of rocks and evaluate influence and scale-dependency of this process on both earthquakes and landslides mechanics, in order to assess their hazards. A scale-convergence is proposed by selecting two case studies represented by a local fault (the Alto Tiberina Fault - ATF) and a giant-landslide shear surface (related to the Saidmarreh landslide). The ATF is, one of the largest extensional fault system in Central Italy (60 km long) active in the Quaternary while the Saidmarreh landslide is the largest known subaerial non-volcanic landslide on Earth.
Creep tests will be performed on rocks representative for the two case studies by using a biaxial apparatus, BRAVA within a pressure vessel in order to simulate a true-triaxial stress field. Two types of experiments will be run: 1) constant displacement rate experiments to determine slip zone strength, and 2) creep experiments to evaluate the evolution of slip behavior (i.e. seismic or aseismic). Our unique and innovative laboratory results will be compared to the boundary conditions observed in the study areas and will help to model the slip behaviour and its triggering effects of the two case studies. These data and models will have a considerable impact on the scientific community due to both the unicity of the acquired dataset and the relevance of the proposed case studies.
Slow deformation and fracturing are the main physical mechanisms that lead towards failure episodes, such as earthquake ruptures and massive slope failures. Field observations routinely monitor the slow deformation and accelerating seismic event rates that precede macroscopic failure of the crust. Laboratory experiments allow to relate applied stress and the evolution of crack damage by describing the microcrack interaction, growth and coalescence into major fractures. Such a damaging effect can be regarded as responsible for the progressive rock failure at a slope scale (Eberhardt et al., 2004). Our current lack of understanding the creeping process on both landslides and earthquakes has recently been highlighted by UNESCO, and "Understanding Slow Deformation before Dynamic Failure" was one of the two priority areas for study within the Natural Hazards theme of its International Year of Planet Earth (Ventura et al., 2010).
With the proposed project, we will measure and characterize, for the first time, the conditions that lead carbonate bearing fault zones to creep seismically or aseismically. The characterization of such processes, for the lithologies involved in faulting along the Alto Tiberina Fault and in the landslide movement of the Saidmarreh rockslide, will allow us to quantitatively characterize the conditions needed at crustal scale for creep to occur in one of the largest fault of Italy (ATF) and in the largest ancient landslide in the world (Saidmarreh).
The ATF is, in fact, a 60 km long extensional fault system in Central Italy active in the Quaternary (Barchi et al., 1998; Boncio et al., 2000) and dominated at depth by an east-dipping low angle normal fault (dip 15°-25°). This fault bounds the western flank of the high Tiber Quaternary basin and has accumulated a minimum time-averaged long-term slip rate of about 1-3 mm/yr in the last 2 Myear (Collettini and Holdsworth, 2004, Mirabella et al., 2011) without large historical events unambiguously associated with this fault i.e. most of the ATF fault zone should slip aseismically or creep (Chiaraluce et al., 2007). To be noted that due to its dimension the ATF could generate a M>7 earthquake if deformation would accommodate without aseismic creep.
The Saidmarreh rock avalanche, first described by J. V. Harrison and N. L. Falcon in the 1930s, located in Iran, is the largest known subaerial non-volcanic landslide on Earth. The volume of its debris (44 Gm3) is approximately equal to that of the largest known subaerial landslide of any kind, the 100 ka collapse of Mount Shasta volcano (45 Gm3) and approaches those of gigantic landslides on Mars. The landslide initiated as an immense rockslide detached from a 15 m long portion of the NE flank of Kabir-Kuh anticline, the longest in the Zagros fold-thrust belt (Sepehr and Cosgrove, 2004) and involved a sequence of NE-dipping Cretaceous to Miocene carbonates and mudrocks of the Papdeh formation capped by the stiff Asmari Limestone (Setudehnia and Perry 1967; Takin et al., 1970). Due to their huge geologic relevance, these two case studies represent very interesting case studies from the scientific point of view.
The used deformation apparatus BRAVA is one of the few experimental apparatuses worldwide that can run creep tests under true triaxial conditions overcoming the technical limits that did not allow this kind of tests in the past. With this apparatus, is possible to contemporaneously apply the three different main stresses s1, s2 and s3 to the sample allowing to perform realistic simulation of the boundary conditions acting at crustal scale. Stress-strain numerical analysis will allow to develop appropriate scaling factors in order to apply data at crustal scale shedding lights on large scale creep processes and related triggering processes of two very interesting areas with possible applications worldwide. Moreover, the use of LEMs will improve the erosion rate estimation through the definition of landscape scenarios evolving in continuum, to be constrained by the classical analysis of geomorphic markers. This will help in understanding how the erosion rate could enhance (Larsen and Montgomery, 2012) or inhibit (Bozzano et al., 2016) the landslide proneness.
These data and models will have thus, a significant impact on the scientific community due to both the unicity of the acquired dataset and the relevance of the proposed case studies.