Fast and Localized Temperature Measurements During Simulated Earthquakes in Carbonate Rocks

The understanding of earthquake physics is hindered by the poor knowledge of fault strength and temperature evolution during seismic slip. Experiments reproducing seismic velocity (~1 m/s) allow us to measure both the evolution of fault strength and the associated temperature increase due to frictional heating. However, temperature measurements were performed with techniques having insufficient spatial and temporal resolution. Here we conduct high velocity friction experiments on Carrara marble rock samples sheared at 20 MPa normal stress, velocity of 0.3 and 6 m/s, and 20 m of total displacement. We measured the temperature evolution of the fault surface at the acquisition rate of 1 kHz and over a spatial resolution of ~40 µm with an optical fiber conveying the infrared radiation to a two-color pyrometer. Temperatures up to 1,250 degrees C and low coseismic fault shear strength are compatible with the activation of grain size dependent viscous creep

Friction during earthquakes: 25 years of experimental studies

Notas: Export Date: 21 March 2022Dynamic fault strength (rock friction in the broad sense) and its evolution with seismic slip and slip rate are among the most relevant parameters in earthquake mechanics. Given the large slip rate (1 m s-1 on average), displacement (up to tens of meters), effective stress (tens of MPa), typical of seismic faulting at depth, thermo-mechanical effects become outstanding: dynamic fault strength is severely affected by fluid and rock phase changes, extreme grain size reduction, and the production of amorphous and unstable materials in the slipping zone. Here, first we will summarize the most relevant findings about dynamic fault strength during seismic slip mainly obtained thanks to the exploitation of dedicated experimental machines (i.e., rotary shear apparatus). However, the interpretation of this experimental dataset remains debated because of technical limitations which impede us to measure fundamental parameters such as temperature, strain rate, pore fluid pressure and grain size in the slipping zone. Without a sound estimate of these physical parameters, any constitutive law proposed to describe the evolution of dynamic fault strength during simulated seismic slip remains speculative. Then, we will discuss the results of some recent experiments which exploit new technical approaches to overcome the main limitations of the previous studies. The experimental approach, together with field studies of the geometry and architecture of exhumed faults and modelling, remains our most powerful tool to investigate seismic-related deformation mechanisms in both natural and human-induced earthquakes

fault gouge graphitization as evidence of past seismic slip

One moderate- to large-magnitude earthquake (M > 6) nucleates in Earth's crust every three days n average, but the geological record of ancient fault slip at meters-per-second seismic velocities (as opposed to subseismic slow-slip creep) remains debated because of the lack of established fault-zone evidence of seismic slip. Here we show that the irreversible temperature-dependent transformation of carbonaceous material (CM, a constituent of many fault gouges) into graphite is a reliable tracer of seismic fault slip. We sheared CM-bearing fault rocks in the laboratory at just above subseismic and at seismic velocities under both water-rich and water-deficient conditions and modeled the temperature evolution with slip. By means of micro-Raman spectroscopy and focused-ion beam transmission electron microscopy, we detected graphite grains similar to those found in the principal slip zone of the A.D. 2008 Wenchuan (Mw 7.9) earthquake (southeast Tibet) only in experiments conducted at seismic velocities. The experimental evidence presented here suggests that high-temperature pulses associated with seismic slip induce graphitization of CM. Importantly, the occurrence of graphitized fault-zone CM may allow us to ascertain the seismogenic potential of faults in areas worldwide with incomplete historical earthquake catalogues

Architecture and seismic markers of an exhumed fault zone in dolostones (Foiana line, Italian Southern Alps).

The earthquake sequences of Bovec 1998 (strike-slip focal mechanism, MD 5.6), L'Aquila 2009 (normal, Mw 6.1) and Emilia 2012 (thrust, Mw 6.0) had the main shocks ruptures propagating and several foreshocks and aftershock nucleating within sedimentary successions mostly made of carbonatic rocks. These earthquake sequences are often long lasting (several months to years) and follow a complex spatiotemporal evolution, which is probably the result of the geometry of the fault-fracture network, fault rock distribution, ingression of uids, etc. Seismic waves inversion analysis has limited spatial resolution (in most cases > 1 km), and does not allow to reconstruct the geometrical complexity of fault zones and the distribution of fault rocks. Here the need of dedicated studies, from metric to kilometric scale ("multiscalar") of the architecture of faults hosted in carbonatic sedimentary rocks. This information, associated with mechanical data obtained from friction and rupture experiments, could be used in physically-based earthquake forecasting models and in simulation of seismic ruptures for earthquake hazard studies. In this thesis, I used a multidisciplinary approach which includes remote sensing analysis, detailed geological eld survey and microstructural studies to quantify the architecture of the 30 km long north-south striking Foiana Fault Zone (FFZ, Linea della Foiana auctores: Val di Non, Italian Southern Alps). The FFZ activity lasted from the Permian (mainly normal faulting) to the Miocene (mainly strike-slip faulting). In the Val di Non area, the FFZ is mainly hosted in Triassic dolostones (Sciliar Fm.), was exhumed from 1.5 km (southern segment) to 2.5 km (central segment) depth and, in his southern part, curves to the south-west into a restraining bend producing a fault-propagation anticline. As discussed here, the FFZ underwent seismic activity during the Miocene as attested by eld and microstructural evidences. The remote sensing analysis, thanks to the high resolution (2.5 to 1 m) 7 of the LIDAR-based digital terrain models images, allowed a detailed reconstruction of the structural lineaments of the FFZ and neighbor areas. The lineaments were organized in groups based on their strike. The Riedel-shear model was used to interpret their geometrical arrangement, which was consistent with the left-lateral kinematics of the FFZ. Detailed structural eld geology survey (which included systematic rock sampling) was performed in three localities (from south to the north: Carnalez, Salobbi and Doss de la Ceora) covering a ca. 7 km long segment of the southern part of the FFZ. I traced sections parallel and orthogonal to fault strike to determine the attitude and spacing of the main structural features (faults, joints, bedding, etc.) and the distribution and characteristics of the fault zone rocks. An intriguing aspect was the presence of large volumes (up to 300 m in thickness) of in-situ shattered (fracture density from 3 cm to few mm) dolostones with negligible or null shear strain, cut by ultracataclastic slipping zones with mirror-like surfaces. The presence of clasts truncated by the mirror-surfaces and of clasts with radial fractures ("exploded" grains) immersed in the ne matrix of the ultracataclasites, is indicative of the seismic origin of these fault rocks, consistently with recent experiments reproducing seismic slip deformation conditions. In general, the attitude of the minor faults of the FFZ evolves from scattered with dominant reverse dip-slip reverse component in the southern exposures (Carnalez) to sub-parallel faults with dominant strike-slip towards the northern exposures (Doss de la Ceora). This major change in the architecture of the FFZ is concomitant with a decrease in the thickness of the damage zone (in-situ shattered dolostones) from 300 m in Carnalez to 200 m in Doss de la Ceora. These architectural along strike variations are here interpreted as the result of the presence of southern fault bend or of dynamic coseismic rupture processes. In the latter case, the larger scatter in the attitude (and sense of shear) of the fault-fracture network with respect to the northern exposures may reect rupture directivity eects and the dierent depth of seismic faulting (larger the pressure connement, larger the scatter of the attitude of the faults), consistently with recently published earthquake simulations models. Lastly, the pre-existing bedding surfaces appeared to be primary factor in controlling the nucleation of slip surfaces and fault zone thickening and growth during progressive deformation.ope

Evoluzione microstrutturale con il rigetto in faglie sismogenetiche in tonalite (faglia delle Gole Larghe, Adamello, Italia)

The fabric of fault rocks (existence of foliations, matrix vs fragments ratio, etc.) is one of the parameters which influences the whole mechanic behavior of a fault, since the aseismic to the coseismic phases. In experiments driven in room humid-ity and temperature conditions on the same non cohesive fault rocks, was ob-served that fabric and frictional properties (for example the possibility of enucle-ating seismic ruptures) show an evolution with displacement. Nowadays, data on natural samples regarding the evolution of fabric with displacement are missing. It must be considered that in nature is also present, next to the mechanic role of abrasion and comminution, chemical processes like the fluids action on the rock during fragmentation (mineral dissolution, secondary mineral precipitation, etc.). In this work are studied the fabric and the clast size distribution of fault rocks sampled from the Gole Larghe Fault Zone, Adamello (Southern Alps). The sam-ples selected belong to seismogenic faults with cataclasites and pseudotachilites, which displacement grows from 0 to 9.8 centimeters. These faults were active at the base of the seismogenetic crust (9-11 km depth and 250-280 Celsius). The fabric of the fault rocks is studied from four SEM-BSE images, taken at 100X and 400X magnifications, for each of the two samples. Clast size distribu-tion, shape factors and orientation are going to be calculated using image analysis techniques. The data obtained this way are discussed, also thanks to experimental observations from literature, in order to determine the main deformative process-es undergoing in the fault during the seismic cycle

Architecture and seismic markers of an exhumed fault zone in dolostones (Foiana line, Italian Southern Alps).

The earthquake sequences of Bovec 1998 (strike-slip focal mechanism, MD 5.6), L'Aquila 2009 (normal, Mw 6.1) and Emilia 2012 (thrust, Mw 6.0) had the main shocks ruptures propagating and several foreshocks and aftershock nucleating within sedimentary successions mostly made of carbonatic rocks. These earthquake sequences are often long lasting (several months to years) and follow a complex spatiotemporal evolution, which is probably the result of the geometry of the fault-fracture network, fault rock distribution, ingression of uids, etc. Seismic waves inversion analysis has limited spatial resolution (in most cases > 1 km), and does not allow to reconstruct the geometrical complexity of fault zones and the distribution of fault rocks. Here the need of dedicated studies, from metric to kilometric scale ("multiscalar") of the architecture of faults hosted in carbonatic sedimentary rocks. This information, associated with mechanical data obtained from friction and rupture experiments, could be used in physically-based earthquake forecasting models and in simulation of seismic ruptures for earthquake hazard studies. In this thesis, I used a multidisciplinary approach which includes remote sensing analysis, detailed geological eld survey and microstructural studies to quantify the architecture of the 30 km long north-south striking Foiana Fault Zone (FFZ, Linea della Foiana auctores: Val di Non, Italian Southern Alps). The FFZ activity lasted from the Permian (mainly normal faulting) to the Miocene (mainly strike-slip faulting). In the Val di Non area, the FFZ is mainly hosted in Triassic dolostones (Sciliar Fm.), was exhumed from 1.5 km (southern segment) to 2.5 km (central segment) depth and, in his southern part, curves to the south-west into a restraining bend producing a fault-propagation anticline. As discussed here, the FFZ underwent seismic activity during the Miocene as attested by eld and microstructural evidences. The remote sensing analysis, thanks to the high resolution (2.5 to 1 m) 7 of the LIDAR-based digital terrain models images, allowed a detailed reconstruction of the structural lineaments of the FFZ and neighbor areas. The lineaments were organized in groups based on their strike. The Riedel-shear model was used to interpret their geometrical arrangement, which was consistent with the left-lateral kinematics of the FFZ. Detailed structural eld geology survey (which included systematic rock sampling) was performed in three localities (from south to the north: Carnalez, Salobbi and Doss de la Ceora) covering a ca. 7 km long segment of the southern part of the FFZ. I traced sections parallel and orthogonal to fault strike to determine the attitude and spacing of the main structural features (faults, joints, bedding, etc.) and the distribution and characteristics of the fault zone rocks. An intriguing aspect was the presence of large volumes (up to 300 m in thickness) of in-situ shattered (fracture density from 3 cm to few mm) dolostones with negligible or null shear strain, cut by ultracataclastic slipping zones with mirror-like surfaces. The presence of clasts truncated by the mirror-surfaces and of clasts with radial fractures ("exploded" grains) immersed in the ne matrix of the ultracataclasites, is indicative of the seismic origin of these fault rocks, consistently with recent experiments reproducing seismic slip deformation conditions. In general, the attitude of the minor faults of the FFZ evolves from scattered with dominant reverse dip-slip reverse component in the southern exposures (Carnalez) to sub-parallel faults with dominant strike-slip towards the northern exposures (Doss de la Ceora). This major change in the architecture of the FFZ is concomitant with a decrease in the thickness of the damage zone (in-situ shattered dolostones) from 300 m in Carnalez to 200 m in Doss de la Ceora. These architectural along strike variations are here interpreted as the result of the presence of southern fault bend or of dynamic coseismic rupture processes. In the latter case, the larger scatter in the attitude (and sense of shear) of the fault-fracture network with respect to the northern exposures may reect rupture directivity eects and the dierent depth of seismic faulting (larger the pressure connement, larger the scatter of the attitude of the faults), consistently with recently published earthquake simulations models. Lastly, the pre-existing bedding surfaces appeared to be primary factor in controlling the nucleation of slip surfaces and fault zone thickening and growth during progressive deformation

High velocity friction data and thermochemical modeling data of smectite-rich STx-1b (vacuum dry, room humidity and water partly saturated)

The dataset is described also in the readme.txt file as follows: The columns are organized as follows: * Time [milliseconds]: time * Normal [MPa]: normal stress * Slip [m]: equivalent displacement * Vel [m/s]: equivalent tangential velocity * Shear1 [MPa]: shear stress * Mu1 []: friction coefficient = shear stress / normal stress * Thick [mm]: thickness of the gouge layer measured with the low resolution LVDT * Thick_high [mm]: thickness of the gouge layer measured with the high resolution LVDT Models Subfolder \model\ Each filename is the experiment’s name and is in .CSV format. The header for all the tables is in a separate file: header.CSV. The columns are organized as follows: * Time [seconds]: time * U_1 [°C]: temperature in node 1 * U_20 [°C]: temperature in node 20 * Qso [°C/s]: temperature source * Qsi1 [°C/s]: temperature sink of reaction 1 (smectite interlayer dehydration) * Qsi2 [°C/s]: temperature sink of reaction 2 (smectite dehydroxylation) * U2_1 [MPa]: pressure in node 1 * U2_20 [MPa]: pressure in node 20 * Thpress [Pa/s]: pressure source for thermal pressurization * Omega1 [Pa/s]: pressure source for reaction 1 (smectite interlayer dehydration) * Omega2 [Pa/s]: pressure source for reaction 2 (smectite dehydroxylation) * R1_1 []: reacted fraction for reaction 1 (smectite interlayer dehydration) * R2_1 []: reacted fraction for reaction 2 (smectite dehydroxylation