Variations in slip-rate and earthquake occurrence across 3D structural complexities on active normal faults

This PhD thesis provides a series of studies on the relationship between the non-planar geometry and the seismic behaviour of active normal faults. Herein, several examples show that throw and fault dip increase within along-strike fault bends in order to preserve the horizontal strain-rate within the bend and along the fault. This has been demonstrated for a variety of normal faults (a) located in different geodynamic domains and (b) for measurements of throw taken over different time periods. Furthermore, throw enhancement within fault bends has been observed on (1) immature faults, where fault bends are still propagating up to the surface and are not yet fully established, (2) well-established single fault segments, where fault bends affect one continuous fault segment, and (3) densely-spaced fault systems arranged across strike (with fault spacing < 5 km), where a change in strike across several fault segments creates an overall bend in the system. The results presented in this thesis suggest that the relationship between the non-planar geometry and the distribution of throw is scale-independent, and can act across systems of faults if they are closely spaced across strike. Moreover, 36Cl-cosmogenic dating of tectonically-exposed fault planes on faults spaced > 5 km across-strike shows that these faults are clustered, with a non-systematic alternance of periods of rapid slip accumulation (i.e. earthquake clustering) and periods of quiescence (i.e. earthquake anti-clustering); this suggests that parallel faults interact in terms of sharing the regional strain-rate, with switching activity that affects the slip-rate on a single fault. The results have implications for numerous and diverse aspects of the earthquake geology, such as interpretation of palaeoseismology studies including at trench sites and cosmogenic dating of fault planes, empirical scaling relationships, PSHA, and off-fault deformation

Variations in slip-rate and earthquake occurrence across 3D structural complexities on active normal faults

This PhD thesis provides a series of studies on the relationship between the non-planar geometry and the seismic behaviour of active normal faults. Herein, several examples show that throw and fault dip increase within along-strike fault bends in order to preserve the horizontal strain-rate within the bend and along the fault. This has been demonstrated for a variety of normal faults (a) located in different geodynamic domains and (b) for measurements of throw taken over different time periods. Furthermore, throw enhancement within fault bends has been observed on (1) immature faults, where fault bends are still propagating up to the surface and are not yet fully established, (2) well-established single fault segments, where fault bends affect one continuous fault segment, and (3) densely-spaced fault systems arranged across strike (with fault spacing < 5 km), where a change in strike across several fault segments creates an overall bend in the system. The results presented in this thesis suggest that the relationship between the non-planar geometry and the distribution of throw is scale-independent, and can act across systems of faults if they are closely spaced across strike. Moreover, 36Cl-cosmogenic dating of tectonically-exposed fault planes on faults spaced > 5 km across-strike shows that these faults are clustered, with a non-systematic alternance of periods of rapid slip accumulation (i.e. earthquake clustering) and periods of quiescence (i.e. earthquake anti-clustering); this suggests that parallel faults interact in terms of sharing the regional strain-rate, with switching activity that affects the slip-rate on a single fault. The results have implications for numerous and diverse aspects of the earthquake geology, such as interpretation of palaeoseismology studies including at trench sites and cosmogenic dating of fault planes, empirical scaling relationships, PSHA, and off-fault deformation

Rheological changes in melts and magmas induced by crystallization and strain rate

This review highlights the rheological and phase proportions variation induced by cooling events from superliquidus temperature (melt) to subliquidus temperatures. It provides a comprehensive view of the rheological response of magmatic systems undergoing dynamic cooling and shear deformation. The two main parameters which are of importance to model the rheological properties of such crystallizing systems and which are simultaneously poorly investigated so far are crystallization and strain rates. The response to relatively high deformation rates results in shear thinning behavior in partly crystallized systems under variable shear rate and it should be considered in magmatic processes. Due to the sluggish crystallization of SiO2-rich melts, data are mainly available for mafic systems, which does not allow a general reappraisal. An attempt to model available literature data for less evolved systems in dynamic scenarios and a comparison with MELTS algorithm approach (thermodynamic equilibrium conditions) is provided. Since there are difficulties in comparing experimental data gained using different methodologies, we focus mainly on data obtained with the concentric cylinder technique. This highlights the fact that a general experimental protocol is needed in order to compare and model viscosity data to predict the dynamic rheological evolution for volcanic rocks. © Académie des sciences, Paris and the authors, 2022. Some rights reserved

The Onset and Solidification Path of a Basaltic Melt by in situ Differential Scanning Calorimetry (DSC) and ex situ Investigations

The in situ differential scanning calorimetry (DSC) technique has been applied to investigate the solidification paths of a basaltic liquid. The starting glass was heated up to 1300°C, kept at this superliquidus temperature for 2 h and cooled at rates (ΔT/Δt) of 7, 60, 180, 1000, and 1800°C/h, down to 800 and 600°C. Glass transition temperature (Tg), crystallization temperature (Tx_HR) and melting temperature (Tm) were measured by in situ DSC spectra on heating. Tx measured along the cooling paths (Tx_CR) shows exothermic peaks that change from a single symmetric shape (7 and 60°C/h) to multi-component patterns (180, 1000, and 1800°C/h). The recovered products characterized by field emission gun source of the scanning electron microscopy and electron probe micro-analyzer-wavelength dispersive spectrometers show a phase assemblage of spinel (sp), clinopyroxene (cpx), melilite (mel), plagioclase (plg), and glass. Moreover, crystal size distributions (CSDs) and growth rates (Gmax and GCSD) were also determined. The crystal content slightly increases from 7 to 1800°C/h. Faceted sp are present in all the run products with an amount always <2 area%. Cpx increases from 7 to 1800°C/h, changing its texture from almost faceted to dendritic between 60 and 180°C/h. The area% of mel follows an asymmetric Gaussian trend, while plg nucleates only at 7°C/h with a content <2 area%. The coupling of DSC and SEM outcomes indicate that sp nucleate first, followed by cpx and mel (and/or plg). The increment of ΔT/Δt causes an increase of the CSD slope (m) and crystal population density per size (n0), as well as a decrease of the crystal size, for both cpx and sp. The log-linear CSD segments with different slopes at 7 and 60°C/h suggest multiple nucleation events and crystal growth by coarsening. Gmax and GCSD for cpx and sp directly measured on the actual crystallization time by DSC spectra, both increase with the increasing of ΔT/Δt. The onset temperature of crystallization (Txi) decreases as ΔT/Δt increases, following an exponential trend that defines the uppermost portion of a time-transformation-temperature-like curve. This analytical model allows us to quantitatively model the kinetic crystallization paths of dry basalts

Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from 36Cl cosmogenic exposure dating and decadal GPS strain-rate

To assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ 36Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for 36Cl analyses. Results from Bayesian inference of the measured 36Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30–75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods

Occurrence of partial and total coseismic ruptures of segmented normal fault systems: insights from the Central Apennines, Italy

Normal faulting earthquakes rarely rupture the entire extent of active normal faults, and can also jump between neighbouring faults. This confounds attempts to use segmentation models to define the likelihood of future rupture scenarios. We attempt to study this problem comparing the offsets produced in single earthquakes with those produced by multiple earthquakes over longer timescales, together with detailed studies of the structural geology. We study the active normal fault system causative of the Mw 6.3 2009 L’Aquila earthquake in central Italy, comparing the spatial distribution of coseismic offsets, cumulative offsets that have developed since 15 ±3 ka, and the total offsets that have accumulated since the faults initiated at 2-3 Ma. Our findings suggest that: 1) faults within a segmented fault system behave as a single interacting fault segment over time periods including multiple earthquake cycles (e.g. 2-3 Ma or 15±3ka), with single earthquakes causing either partial or total ruptures of the entire system; 2) an along-strike bend causes throw and throw-rates enhancements within the bend throughout the seismic history of the fault system. We discuss the synchronised and geometrically controlled activity rates on these faults in terms of the propensity for floating earthquakes, multi-fault earthquakes, and seismic hazard

Comparative In Vitro Evaluation of the Primary Stability in D3 Synthetic Bone of Two Different Shapes and Pitches of the Implant Threads

Background: Implant primary stability can be affected by several factors related to implant macrogeometry, local anatomy, and surgical techniques. The aim of this research was to study primary stability on polyurethane foam sheets of wide‐threaded implant design compared to narrow‐threaded implants. Materials and methods: Two different implant designs were positioned on D3 density polyurethane blocks in a standardized environment: the wide‐threaded implant and the narrow‐threaded implant, for a total of 160 specimens. Moreover, for each group, two different sizes were considered: 3.8mm × 12mm and 4.8mm × 12 mm. The insertion torque (IT) values, the removal strength (RT), and the Periotest analyses were evaluated. Results: A significantly higher IT and RT was reported for wide‐threaded implants and two‐stage implants (p &lt; 0.01), compared to the narrow‐threaded implants. The diameters seemed to provide a significant effect on the primary stability for both implants’ geometry (p &lt; 0.01). A higher mean of the one‐stage implant was evident in the Periotest measurements (p &lt; 0.01). Conclusions: Both of the implants showed sufficient stability in polyurethane artificial simulation, while the wide‐threaded implant design showed a higher primary stability on alveolar cancellous synthetic bone in vitro. Additionally, the prosthetic joint connection seemed to have a determinant effect on Periotest analysis, and the one‐stage implants seemed to provide a high stability of the fixture when positioned in the osteotomy, which could be important for the immediate loading protocol

S100A8 calcium-binding expression in radicular and dentigerous cysts and in keratocystic odontogenic tumors

Introduction: Recently the term Keratocystic Odontogenic Tumor (KCOT) has been recommended for Odontogenic Keratocysts (OKC) to address the neoplastic nature of the lesion compared to radicular and dentigerous cysts. S100 are calcium-binding proteins involved in cell differentiation and inflammation, with a potential role in neoplastic transformation. Aim: The aim of this study was to evaluate whether S100A8 protein expression is different in KCOT compared to radicular cysts (RC) and dentigerous cysts (DC). Methods: A total of 84 consecutive odontogenic cysts, 34 RC, 25 DC, and 25 KCOT, were analyzed in this study. Results: Epithelial cells in KCOT cases were not immunoreactive for S100A8 except focally in cases associated with inflammation, while RC cases showed a variable positivity of all the epithelial layers from the basal to the superficial in 19/34 cases and DC cases showed a weak positivity of the intermediate and superficial layers in 7/25 cases. Conclusion: The lack of S100A8 protein expression seems to be observed more frequently in KCOT compared to RC and DC. This difference might be related to their neoplastic nature and a potential aggressive biological behavior for odontogenic cystic lesions

Throw-rate variations within linkage zones during the growth of normal faults: case studies from the Western Volcanic Zone, Iceland.

This work investigates how throw-rates vary within fault bends and sites of fault linkage during the process of normal fault growth. In the Western Volcanic Zone, Iceland, through detailed field mapping and field measurements of fault throws, normal faults are mapped and along-strike throw profiles are constructed in order to understand how the throw-rates relate with the local fault geometry along faults at different stages of linkage. The results show that throw-rates increase within linkage zones and propagating fault bends independently from the stage of maturity of the fault bend. This implies that 1) the relationship between the local fault geometry and the along-strike distribution of throw-rate is driven by the deeper part of the fault, where established fault bends start propagating to the surface; 2) faults grow first by linkage and coalescence of separate faults, and then by accumulation of slip on the resultant fault, in agreement with models of fault growth by linkage and coalescence; 3) incipient fault bends can produce uncertainty associated with palaeoseismological results, if fault bends remain unrecognised. Moreover, this work demonstrates that existing models showing increased co-seismic and throw-rates within fault bends and sites of fault linkage found in continental extensional settings are valid in a geodynamic context of a mid-oceanic rifts