Structure, fluid flow and mechanical, properties of carbonate/clay-hosted seismogenetic faults: case studies from the Central Apennines, Italy

In many seismically active countries (e.g., Italy, Greece, Turkey, China, USA) moderate to large earthquakes nucleate in and propagate through heterogeneous (i.e., consisting of carbonate, marly, and clayey deposits) sedimentary successions within the brittle upper crust (< 5 km depth), often causing surface displacement with associated damages and casualities. In particular, in the central Apennines of Italy, moderate earthquakes (< Mw 7.0) propagate through the heterogeneous carbonatic-clayey sedimentary cover up to the Earth’s surface, possibly causing surface faulting (e.g., 1915, Mw 7.0, Avezzano Earthquake; 2009, Mw 6.3, L’Aquila Earthquake. For instance, the mainshock of the recent Mw 6.0 Amatrice earthquake of August 24th, 2016, nucleated at ~7-8 km depth and the seismic slip propagated upward through carbonate rocks causing a ~6 km long surface rupture and deformation. Indirect studies (i.e., through seismological, geophysical, and geodetic techniques) lack of sufficient spatio-temporal resolution to constrain the detailed three-dimensional fault-zone architecture, the deformation mechanisms, and the seismic-related fluid circulation within seismogenic faults at depth. The study of exposed fault zones exhumed from shallow depth (i.e., depths < 3 km) can narrow this knowledge gap and can help in understanding how the shallow fault zone structure can promote or inhibit seismic slip propagation up to the Earth’s surface. For these reasons, in this thesis, I used a multidisciplinary approach to study exposed carbonate/clay-hosted active faults, which can be reliable analogues of buried seismogenic faults at depth, in the seismogenic domain of the central Apennines, Italy. In particular, I combined fieldwork (geological mapping and structural analysis) with laboratory studies. I used optical microscopy and FESEM (Field Emission Scanning Electron Microscopy) to study fault rock microstructures from micro- to nanoscale. I used stable isotope analyses on calcite veins/cement, whole rock geochemistry, cathodoluminescence, and X-ray powder diffraction to study the origin and paleotemperatures of geofluids, which circulated in the fault zones, and fault rock mineralogy. I used low to high velocity friction experiments (using the Slow to High Velocity Apparatus, SHIVA, at INGV in Rome) to understand fault rock frictional properties during earthquake propagation and in situ mechanical analyses using Atomic Force Microscopy to understand fault rocks elastic properties (Young’s modulus and viscoelasticity) down to nanoscale. In particular, the main focus of this thesis is to understand the roles both of fluids and phyllosilicates during the seismic cycle within carbonate-hosted faults in the shallow carbonate-dominated brittle crust

Ultra-thin clay layers facilitate seismic slip in carbonate faults

Many earthquakes propagate up to the Earth's surface producing surface ruptures. Seismic slip propagation is facilitated by along-fault low dynamic frictional resistance, which is controlled by a number of physico-chemical lubrication mechanisms. In particular, rotary shear experiments conducted at seismic slip rates (1 ms(-1)) show that phyllosilicates can facilitate co-seismic slip along faults during earthquakes. This evidence is crucial for hazard assessment along oceanic subduction zones, where pelagic clays participate in seismic slip propagation. Conversely, the reason why, in continental domains, co-seismic slip along faults can propagate up to the Earth's surface is still poorly understood. We document the occurrence of micrometer-thick phyllosilicate-bearing layers along a carbonate-hosted seismogenic extensional fault in the central Apennines, Italy. Using friction experiments, we demonstrate that, at seismic slip rates (1 ms(-1)), similar calcite gouges with pre-existing phyllosilicate-bearing (clay content ≤3 wt.%) micro-layers weaken faster than calcite gouges or mixed calcite-phyllosilicate gouges. We thus propose that, within calcite gouge, ultra-low clay content (≤3 wt.%) localized along micrometer-thick layers can facilitate seismic slip propagation during earthquakes in continental domains, possibly enhancing surface displacement

The minimum scale of grooving on a recently ruptured limestone fault

AbstractFaults have grooves that are formed by abrasion and wear during slip. Recent observations indicate that this grooving is only a large‐scale feature, indicating brittle behavior has a length scale limit. The connection between this scale and earthquake behavior remains limited because no examples exist from a proven seismogenic fault. Here, we address this problem and analyze differences in this scale between lithologies to further our understanding of the underlying mechanics. This study uses samples from the Mt. Vettoretto fault collected after the Norcia earthquake of 2016. We imaged fault topography with a white light interferometer and 10 μm resolution structure from motion and then calculated a Monte Carlo version of root mean square roughness. We found a minimum scale of grooving of ~100 μm. In comparing this fault to the Corona Heights fault, we find that this minimum grooving scale is consistent with predictions based on material properties

Complex geometry and kinematics of subsidiary faults within a carbonate-hosted relay ramp

Minor fault geometry and kinematics within relay ramps is strongly related to the stress field perturbations that can be produced when two major fault segments overlap and interact. Here we integrate classical fieldwork and interpretation of a virtual outcrop to investigate the geometry and kinematics of subsidiary faults within a relay ramp along the Tre Monti normal fault in the Central Apennines. Although the Tre Monti fault strikes parallel to the regional extension (NE-SW) it shows predominant dip-slip kinematics, suggesting a NW-SE oriented extension acting at sub-regional scale (1–10 km). Conversely, the slickenlines collected on the front segment of the relay ramp highlight right-lateral kinematics. The subsidiary faults in the relay ramp show a complex geometry (variable attitudes) and slickenlines describe multiple kinematics (left-lateral, dip-slip, right-lateral), independently of their orientation. Our fault slip analysis indicates that a local stress field retrieved from the kinematic inversion of the slickenlines collected on the front segment, and likely promoted by the interaction between the overlapping fault segments that bound the relay zone, can explain most of the geometry and kinematics of the subsidiary faults. Further complexity is added by the temporal interaction with both the regional and sub-regional stress fields

Available raw data collected in the Simbruini-Ernici Ridge and discussed in the paper: Shallow deformation in subduction zones: microstructural evidence for aseismic slip and low frequency tremor in molasse-type conglomerates from the Central Apennines accretionary wedge

This file contains uninterpreted geological data collected in the Simbruini-Ernici Ridge such as field photos, microphotos and SEM photos, along with coordinates of sampling localities and main structural data. Data are made available for supporting the paper: Shallow deformation in subduction zones: microstructural evidence for aseismic slip and low frequency tremor in molasse-type conglomerates from the Central Apennines accretionary wedg

Photogrammetric 3D model via smartphone GNSS sensor. Workflow, error estimate, and best practices

Geotagged smartphone photos can be employed to build digital terrain models using structure from motion-multiview stereo (SfM-MVS) photogrammetry. Accelerometer, magnetometer, and gyroscope sensors integrated within consumer-grade smartphones can be used to record the orientation of images, which can be combined with location information provided by inbuilt global navigation satellite system (GNSS) sensors to geo-register the SfM-MVS model. The accuracy of these sensors is, however, highly variable. In this work, we use a 200 m-wide natural rocky cliff as a test case to evaluate the impact of consumer-grade smartphone GNSS sensor accuracy on the registration of SfM-MVS models. We built a high-resolution 3D model of the cliff, using an unmanned aerial vehicle (UAV) for image acquisition and ground control points (GCPs) located using a differential GNSS survey for georeferencing. This 3D model provides the benchmark against which terrestrial SfM-MVS photogrammetry models, built using smartphone images and registered using built-in accelerometer/gyroscope and GNSS sensors, are compared. Results show that satisfactory post-processing registrations of the smartphone models can be attained, requiring: (1) wide acquisition areas (scaling with GNSS error) and (2) the progressive removal of misaligned images, via an iterative process of model building and error estimation

Pop-up structure in massive carbonate-hosted fold-and-thrust belt. Insight from field mapping and 2D kinematic model in the central Apennines

Fold-and-thrust belts are characterized by the occurrence of foreland-verging thrusts and antithetic backthrust, which develop in the hangingwall of thrust sheets. Both thrust and backthrust bound the so-called pop-up structure, which is a deformed zone characterized by thrust- and backthrust-related anticlines. Pop-up structures mainly develop in fold-and-thrust belts characterized by a multilayered sedimentary sequence, consisting of limestones, marls, and shales, deformed above a weak décollement, such as evaporites. However, in this work, we combine field mapping, stratigraphic constrains, and structural analysis with 2D kinematic forward modeling to document a pop-up structure developed within limestones/dolostones, deformed above a strong décollement consisting of dolostones, in the central Apennines, Italy. In particular, we describe a SW-verging anticline and a NE-verging anticline in the SW and NE margin of the Serra Lunga ridge, respectively. Such folds were generated by a NE-dipping backthrust and by SW-dipping forethrust, respectively. Therefore, we suggest that the Serra Lunga ridge represents a pop-up structure, showing geometries similar to other pop-up structures observed within fold-and-thrust belts characterized by a multilayered sedimentary sequence. In addition, backlimb tilting of backthrust-related anticlines generates the forelandward-dipping monoclines, observed within thrust sheets in the Central Apennines and in several fold-and-thrust belts worldwide

Variation in structural styles within fold-and-thrust belts: Insights from field mapping, cross-sections balancing, and 2D-kinematic modelling in the Jura mountains (Eastern France)

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Lithological control on multiple surface ruptures during the 2016–2017 Amatrice-Norcia seismic sequence

On August 24th 2016, a Mw 6.0 earthquake started the Amatrice - Norcia (Central Italy) seismic sequence, generated by the extensional tectonics along the Apennines, that had its apex with the Mw 6.5 October 30th mainshock. As a unique documented case reported in Italy, complex surface faulting occurred during both earthquakes along the Mt. Vettore fault. Multiple surface faulting was accompanied at depth by the development of a km-scale normal fault-propagation fold. This fold was characterized by breakthrough and by surface rupture within thick carbonatic layers only in the central and north-western area (Mt. Vettore). On the contrary, the fault remained blind where flexural slip was active in sandy-silty turbiditic deposits in the south-eastern area (Mt. Gorzano). We explain the different faulting behaviour with the occurrence of more rigid and competent lithologies in areas characterized by breakthrough and with the occurrence of weaker lithologies in areas characterized by blind faulting. Overall, the entire seismic sequence appears as a gradual gravitational adjustment of the hangingwall block, slipping along a NW-trending and 80 km long fault system. In particular, the following crustal blocks, partially overlapping and with different length (30, 40 and 22 km, respectively), progressively collapsed during the sequence: the Amatrice sector during the August 24th 2016, Mw 6.0 event, the Norcia-Visso sector during the October 26th 2016, Mw 5.9 and the 2016 October 30th Mw 6.5 event, and the Campotosto Lake sector during the four January 18th 2017, M>5 events. The progressive involvement of these three rock volumes, during the seismic sequence is here explained by the occurrence of a low angle detachment that limited the maximum potential depth of the mainshocks and consequently the dimensions of involved rock volumes, therefore limiting the magnitudes of the mainshocks.Published1016762T. Deformazione crostale attivaJCR Journa