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  • 1
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    Tidal modulation of plate motions (2020)
    Elsevier
    Details
    Publication Date: 2020-06-01
    Print ISSN: 0012-8252
    Electronic ISSN: 1872-6828
    Topics: Geography , Geosciences
    Published by Elsevier
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  • 2
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    Different Fault Response to Stress during the Seismic Cycle (2021)
    Molecular Diversity Preservation International
    Details
    Publication Date: 2021-10-14
    Description: Seismic prediction was considered impossible, however, there are no reasons in theoretical physics that explicitly prevent this possibility. Therefore, it is quite likely that prediction is made stubbornly complicated by practical difficulties such as the quality of catalogs and data analysis. Earthquakes are sometimes forewarned by precursors, and other times they come unexpectedly; moreover, since no unique mechanism for nucleation was proven to exist, it is unlikely that single classical precursors (e.g., increasing seismicity, geochemical anomalies, geoelectric potentials) may ever be effective in predicting impending earthquakes. For this reason, understanding the physics driving the evolution of fault systems is a crucial task to fine-tune seismic prediction methods and for the mitigation of seismic risk. In this work, an innovative idea is inspected to establish the proximity to the critical breaking point. It is based on the mechanical response of faults to tidal perturbations, which is observed to change during the “seismic cycle”. This technique allows to identify different seismic patterns marking the fingerprints of progressive crustal weakening. Destabilization seems to arise from two different possible mechanisms compatible with the so called preslip patch, cascade models and with seismic quiescence. The first is featured by a decreasing susceptibility to stress perturbation, anomalous geodetic deformation, and seismic activity, while on the other hand, the second shows seismic quiescence and increasing responsiveness. The novelty of this article consists in highlighting not only the variations in responsiveness of faults to stress while reaching the critical point, but also how seismic occurrence changes over time as a function of instability. Temporal swings of correlation between tides and nucleated seismic energy reveal a complex mechanism for modulation of energy dissipation driven by stress variations, above all in the upper brittle crust. Some case studies taken from recent Greek seismicity are investigated.
    Electronic ISSN: 2076-3417
    Topics: Natural Sciences in General
    Published by Molecular Diversity Preservation International
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  • 3
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    Tidal modulation of plate motions (2020)
    Elsevier
    Details
    Publication Date: 2020-09-07
    Description: While mantle convection is a fundamental ingredient of geodynamics, the driving mechanism of plate tectonics remains elusive. Are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them? GPS measurements are now accurate enough that, on long baselines, both secular plate motions and periodic tidal displacements are visible. The now 〉20 year-long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere. We review the data and show that lithospheric plates retain a non-zero horizontal component of the solid Earth tidal waves and their speed correlates with tidal harmonics. High-frequency semidiurnal Earth's tides are likely contributing to plate motions, but their residuals are still within the error of the present accuracy of GNSS data. The low-frequency body tides rather show horizontal residuals equal to the relative motion among plates, proving the astronomical input on plate dynamics. Plates move faster with nu- tation cyclicities of 8.8 and 18.6 years that correlate to lunar apsides migration and nodal precession. The high- frequency body tides are mostly buffered by the high viscosity of the lithosphere and the underlying mantle, whereas low-frequency horizontal tidal oscillations are compatible with the relaxation time of the low-velocity zone and can westerly drag the lithosphere over the asthenospheric mantle. Variable angular velocities among plates are controlled by the viscosity anisotropies in the decoupling layer within the low-velocity zone. Tidal oscillations also correlate with the seismic release.
    Description: Published
    Description: 103179
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Body tide ; Plate tectonics ; Geeodynamics ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Scaling properties of seismicity and faulting (2022)
    Elsevier
    Details
    Publication Date: 2022-04-01
    Description: The Gutenberg–Richter law and the Omori law are both characterized by a scaling behavior. However, their relation is still an open question. Although several hypotheses have been formulated, a comprehen- sive geophysical mechanism is still missing to explain the observed variability of the scaling exponents b-value and p-value, e.g., correlating the seismic cycle to statistical seismology and tectonic processes. In this work, a model for describing the size-frequency scaling and the temporal evolution of seismicity is proposed starting from simple assumptions. The parameter describing how the number of earthquakes decreases after a major seismic event, p, turns out to be positively correlated to the exponent of the frequency-size distribution of seismicity, b, and related to tectonics. Our findings suggest that p ≈ 23 (b + 1). It implies that a relationship between fracturing regimes, “efficiency” of the seismic process, duration of the seismic sequences and geodynamic setting exists, with outstanding potential impact on seismic hazard. On the other hand, the Gutenberg–Richter law simply reflects the tendency of the segments of the Earth’s crust to reach mechanical stability via constrained energy-budget optimization. Each perturbation has a probability of growing an earthquake or not, depending on disorder within the fault zone and the energy accumulated in the adjoining volume, mainly controlling the evolution of seismic sequences. The results are consistent with the different energy sources related to the tectonic settings, i.e., gravitational in extensional regimes, having higher b and p values, and generating lower maximum magnitude earthquakes with respect to strike-slip and contractional settings, which are rather fueled by elastic energy, showing lower b and p values, and they may generate higher magnitude events.
    Description: Published
    Description: 117511
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Keywords: Gutenberg–Richter distribution ; fracturing and fault disorder ; Omori–Utsu law ; earthquake triggering ; tectonic setting ; 04.06. Seismology ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Different Fault Response to Stress during the Seismic Cycle (2022)
    MDPI
    Details
    Publication Date: 2022-02-28
    Description: Seismic prediction was considered impossible, however, there are no reasons in theoretical physics that explicitly prevent this possibility. Therefore, it is quite likely that prediction is made stubbornly complicated by practical difficulties such as the quality of catalogs and data analysis. Earthquakes are sometimes forewarned by precursors, and other times they come unexpectedly; moreover, since no unique mechanism for nucleation was proven to exist, it is unlikely that single classical precursors (e.g., increasing seismicity, geochemical anomalies, geoelectric potentials) may ever be effective in predicting impending earthquakes. For this reason, understanding the physics driving the evolution of fault systems is a crucial task to fine-tune seismic prediction methods and for the mitigation of seismic risk. In this work, an innovative idea is inspected to establish the proximity to the critical breaking point. It is based on the mechanical response of faults to tidal perturbations, which is observed to change during the “seismic cycle”. This technique allows to identify different seismic patterns marking the fingerprints of progressive crustal weakening. Destabilization seems to arise from two different possible mechanisms compatible with the so called preslip patch, cascade models and with seismic quiescence. The first is featured by a decreasing susceptibility to stress perturbation, anomalous geodetic deformation, and seismic activity, while on the other hand, the second shows seismic quiescence and increasing responsiveness. The novelty of this article consists in highlighting not only the variations in responsiveness of faults to stress while reaching the critical point, but also how seismic occurrence changes over time as a function of instability. Temporal swings of correlation between tides and nucleated seismic energy reveal a complex mechanism for modulation of energy dissipation driven by stress variations, above all in the upper brittle crust. Some case studies taken from recent Greek seismicity are investigated.
    Description: Published
    Description: 9596
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Earth’s gradients as the engine of plate tectonics and earthquakes (2022)
    Springer
    Details
    Publication Date: 2022-12-01
    Description: The processes occurring on the Earth are controlled by several gradients. The surface of the Planet is featured by complex geological patterns produced by both endogenous and exogenous phenomena. The lack of direct investigations still makes Earth interior poorly understood and prevents complete clarification of the mechanisms ruling geo- dynamics and tectonics. Nowadays, slab-pull is considered the force with the greatest impact on plate motions, but also ridge-push, trench suction and physico-chemical heterogeneities are thought to play an important role. However, several counterargu- ments suggest that these mechanisms are insufficient to explain plate tectonics. While large part of the scientific community agreed that either bottom-up or top-down driven mantle convection is the cause of lithospheric displacements, geodetic observations and geodynamic models also support an astronomical contribution to plate motions. Moreover, several evidences indicate that tectonic plates follow a mainstream and how the lithosphere has a roughly westerly drift with respect to the asthenospheric mantle. An even more wide-open debate rises for the occurrence of earthquakes, which should be framed within the different tectonic setting, which affects the spatial and temporal properties of seismicity. In extensional regions, the dominant source of energy is given by gravitational potential, whereas in strike-slip faults and thrusts, earthquakes mainly dissipate elastic potential energy indeed. In the present article, a review is given of the most significant results of the last years in the field of geodynamics and earthquake geology following the common thread of gradients, which ultimately shape our planet.
    Description: Published
    Description: 801–881
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Earth’s gradients ; Forces driving plate motions ; Polarized plate tectonics ; Global scale geodynamics ; Earthquake geology ; The role of gradients in seismic dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Tidal drag and westward drift of the lithosphere (2023)
    Elsevier
    Details
    Publication Date: 2023-06-05
    Description: Tidal forces are generally neglected in the discussion about the mechanisms driving plate tectonics despite a worldwide geodynamic asymmetry also observed at subduction and rift zones. The tidal drag could theoretically explain the westerly shift of the lithosphere relative to the underlying mantle. Notwithstanding, viscosity in the asthenosphere is apparently too high to allow mechanical decoupling produced by tidal forces. Here, we propose a model for global scale geodynamics accompanied by numer- ical simulations of the tidal interaction of the Earth with the Moon and the Sun. We provide for the first time a theoretical proof that the tidal drag can produce a westerly motion of the lithosphere, also com- patible with the slowing of the Earth’s rotational spin. Our results suggest a westerly rotation of the litho- sphere with a lower bound of x % ð0:1 0:2Þ /Myr in the presence of a basal effective shear viscosity g % 1016 Pa s, but it may rise to x 〉 1 /Myr with a viscosity of g K 3 1014 Pa s within the Low- Velocity Zone (LVZ) atop the asthenosphere. This faster velocity would be more compatible with the mainstream of plate motion and the global asymmetry at plate boundaries. Based on these computations, we suggest that the super-adiabatic asthenosphere, being vigorously convecting, may further reduce the viscous coupling within the LVZ. Therefore, the combination of solid Earth tides, ultra-low viscosity LVZ and asthenospheric polarized small-scale convection may mechanically satisfy the large-scale decoupling of the lithosphere relative to the underlying mantle. Relative plate motions are explained because of lat- eral viscosity heterogeneities at the base of the lithosphere, which determine variable lithosphere- asthenosphere decoupling and plate interactions, hence plate tectonics.
    Description: Published
    Description: 101623
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Tidal drag ; Lithosphere-asthenosphere interaction ; Plate motions ; Polarized plate tectonics ; Geodynamics ; 04.04. Geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Fault dip vs shear stress gradient (2023)
    Elsevier
    Details
    Publication Date: 2023-06-28
    Description: In the brittle regime, faults tend to be oriented along an angle of about 30° relative to the principal stress direction. This empirical Andersonian observation is usually explained by the orientation of the stress tensor and the slope of the yield envelope defined by the Mohr-Coulomb criterion, often called critical-stress theory, assuming frictional properties of the crustal rocks (μ ≈ 0.6−0.8). However, why the slope has a given value? We suggest that the slope dip is constrained by the occurrence of the largest shear stress gradient along that inclination. High homogeneous shear stress, i.e., without gradients, may generate aseismic creep as for example in flat decollements, both along thrusts and low-angle normal faults, whereas along ramps larger shear stress gradients determine higher energy accumulation and stick-slip behaviour with larger sudden seismic energy release. Further variability of the angle is due to variations of the internal friction and of the Poisson ratio, being related to different lithologies, anisotropies and pre-existing fractures and faults. Misaligned faults are justified to occur due to the local weaknesses in the crustal volume; however, having lower stress gradients along dip than the optimally-oriented ones, they have higher probability of being associated with lower seismogenic potential or even aseismic behavior.
    Description: Published
    Description: 100211
    Description: 2T. Deformazione crostale attiva
    Description: N/A or not JCR
    Keywords: Fault dip ; Tectonic settings ; Shear stress gradients ; Tectonics ; Seismogenic faults ; 04.07. Tectonophysics ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    The impact of faulting complexity and type on earthquake rupture dynamics (2022)
    Nature Publishing Group
    Details
    Publication Date: 2022-10-31
    Description: The statistical properties of seismicity are known to be affected by several factors such as the rheological parameters of rocks. We analysed the earthquake double-couple as a function of the faulting type. Here we show that it impacts the moment tensors of earthquakes: thrust- faulting events are characterized by higher double-couple components with respect to strike- slip- and normal-faulting earthquakes. Our results are coherent with the stress dependence of the scaling exponent of the Gutenberg-Richter law, which is anticorrelated to the double- couple. We suggest that the structural and tectonic control of seismicity may have its origin in the complexity of the seismogenic source marked by the width of the cataclastic damage zone and by the slip of different fault planes during the same seismic event; the sharper and concentrated the slip as along faults, the higher the double-couple. This phenomenon may introduce bias in magnitude estimation, with possible impact on seismic forecasting.
    Description: Published
    Description: 258
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: double couple ; damage zone ; different fault type ; seismicity ; tectonics ; fault type ; seismicity ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Variable seismic responsiveness to stress perturbations along the shallow section of subduction zones: The role of different slip modes and implications for the stability of fault segments (2023)
    Frontiers Media S.A.
    Details
    Publication Date: 2023-03-14
    Description: Assessing the stability state of fault interfaces is a task of primary interest not only for seismic hazards, but also for understanding how the earthquake machine works. Nowadays it is well known that a relationship exists between slow and fast earthquakes; moreover, it is more and more evident that such a connection is quite diffuse all over the Earth. In this paper, we perform a spatial and temporal analysis of both geodetic and seismic—non-volcanic tremors, low-frequency events (LFEs), and regular earthquakes—time series. We focus on the relationship between the clustering of properties of the different kinds of seismicity and their response to stress perturbations. Earth tides and large earthquakes are used as a source of additional stress. Seismic activity hosted in the Cascadia subduction zone, Manawatu region in New Zealand, and Japan during the last two decades is considered. Our analysis suggests that tremors become more and more sensitive to Earth-tide perturbations as the fault interface is seismically locked. Therefore, tremors and regular events show a similar response to tidal stress perturbations. This feature is also accompanied by relatively lower spatial and temporal coefficients of variation. A series of recordings by several GNSS stations along the Hikurangi Trench, North Island, New Zealand, and along the Nankai coasts in Japan is taken into account for studying how large thrust-faulting earthquakes affect silent events and geodetic signals and vice versa. In the last section, a simple model for grasping a glimpse of the local stability condition of the Earth’s crust and for explaining previous observations is provided.
    Description: Published
    Description: 989697
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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