Shallow crustal faults are passive features mobilized by the dissipation of the potential energy ... more Shallow crustal faults are passive features mobilized by the dissipation of the potential energy and the shear stress accumulated in the brittle volume surrounding them. However, the stored energy in the volume differs from the tectonic setting, i.e., it is mainly gravitational in extensional tectonic settings, whereas it is elastic in strike-slip and contractional tectonic environments. In extensional settings, below about 1 km, the horizontal tensile stress is overwhelmed by the confining pressure of the lithostatic load, and it becomes positive, i.e. compressive. Therefore, there is no horizontal tension in extensional tectonic settings and the pro-gravity motion of the crustal volume is provided by the lithostatic load, which is the vertical maximum principal stress. The elastic energy is rather accumulated by the maximum horizontal principal stresses, i.e., iso-gravity in transcurrent settings and counter-gravity in contractional tectonic settings. The different relation with the gravitational force in the different tectonic settings generates several relevant differences in the three main tectonic environments. The extensional tectonic settings, both in continental and oceanic rift zones generate normal fault-related earthquakes, i.e., pro-gravity movements, or graviquakes. They differ from the other tectonic setting because are marked by (i) lower energy and lower differential stress to activate faults with respect to strike-slip and contractional tectonics; (ii) lower maximum earthquake magnitude; (iii) a larger number of low magnitude earthquakes in extensional settings because the crust moves downward as soon as it can move, whereas contractional settings require larger accumulation of energy to move counter-gravity; (iv) consequently, the b-value of the Gutenberg-Richter is higher than 1 and the aftershocks are more numerous and last longer in extensional settings; (v) the downward motion of the hangingwall determines more diffuse cataclastic deformation with respect to the other tectonic settings because the lithostatic load works everywhere, whereas in the other tectonic settings is concentrated where the elastic energy accumulates; (vi) in extensional settings the volume dimension is determined by thickness of the brittle layer, and its length is in average three times the seismogenic thickness; in strike-slip and contractional settings dominates the elastic energy (elastoquakes), and the mobilized volume may be ten to thirty times longer in a single seismic sequence, being its size proportional both to the brittle thickness and the relative speed of plates. These differences characterize the seismic cycle of graviquakes with respect to the elastoquakes. The bigger the volume, the wider the seismogenic fault in all tectonic settings. The interplay between the horizontal tectonic forces and the lithostatic load, which is ubiquitous, varies in the three main tectonic settings, generating different seismotectonic styles and an increase of magnitude as the effect of the vertical gravitational force becomes a minority relative to the elastic storage and coseismic rebound.
Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of ... more Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of seismology, their occurrence has been identified as a possible mechanism leading to further crustal destabilization, hence, to major failures. However, several cases occurred without any previous anomalous seismic activity, so that the hypothesis of foreshocks as reliable seismic precursors fails to pass statistical tests. Here, we perform an all-round statistical comparative analysis of seismicity in Southern California to assess whether any differences can be identified between swarms and foreshocks. Our results suggest that extremely variable seismic patterns can forerun mainshocks, even though they tend to be preceded by clusters with more numerous events spread over larger areas than swarms and with a wider range of magnitudes. We provide a physical explanation of such dissimilarity and conclude, despite it, that foreshocks can hardly be reliable shortterm precursors of large earthquakes in California. Plain Language Summary Large earthquakes can be preceded by a wide range of different seismic anomalies. Among these, seismicity has been reported to increase both in magnitude and frequency, but, on the other hand, it can also undergo a short period of reduced intensity before major events. The first pattern corresponds to the occurrence of foreshocks, that is, small to moderate quakes forewarning an upcoming larger one, while the second behavior is called seismic quiescence. In our research, we focus on foreshock activity. We perform an analysis of seismicity in Southern California, for which a well-provided relocated earthquake catalog is available. While several studies have been conducted so far about what happens before large earthquakes after their occurrence and also there are some works about foreshocks discrimination, a systematic analysis comparing properties of clusters of "swarms", seismicity without a major event, and "foreshocks" before their mainshock is missing. Are foreshocks different from swarms before the occurrence of the main event? Are foreshocks fore-shocks? Our results suggest that foreshocks can hardly be distinguished from swarms until the largest event takes place. On the base of this analysis and theoretical modeling, we think that foreshocks have limited reliability, if considered alone, for short-term forecasts.
The stretching of the lithosphere leading to back-arc basins formation generally develops behind ... more The stretching of the lithosphere leading to back-arc basins formation generally develops behind arctrench systems and is considered the consequence of slab retreat relative to the upper plate. Here, we examine the deformation regime evolution within the overriding plate due to subduction processes, using thermo-mechanical numerical simulations. We explore the northeastern Eurasia plate boundary and the mechanisms of subducting Pacific plate since 57 Ma. During this time interval, several extensional basins formed along the Eurasia margin, such as the East China Sea, the Japan Sea, and the Kuril basin. Here, we increased the simulation complexity, with the inclusion of (i) the kinematic variability of the Pacific plate over the geological past with respect to a fixed Eurasia, incorporating time-dependent (i.e., temporally evolving) velocities computed from plate motion reconstructions; (ii) a Low-Velocity Zone within the asthenosphere, and (iii) a horizontal eastward mantle flow. Our results show a crucial role of the mantle flow for the development of lithospheric extension and back-arc basin opening, and a main kinematic control of the subduction trench position, which advances and retreats, into distance intervals in the order of ∼ 100 km, and providing stages of compression and extension in a back-arc basin.
We propose an innovative methodology for seismic emergency planning and earthquake risk mitigatio... more We propose an innovative methodology for seismic emergency planning and earthquake risk mitigation in central Italy by integrating three prototypal earthquake scenarios. The different scenarios derive maximum earthquake magnitudes from different input data. The first scenario utilizes local rheological, geological, and geophysical conditions; the second scenario considers the study area fault characteristics, while the third scenario relies on the cluster analysis of historical and instrumental earthquake records. The magnitudes and related uncertainties are combined using a conflation method to derive the expected ground motions for a grid of sites in central Italy. The resulting scenarios include peak ground acceleration and spectral ordinates, presented as maps and spectra for two selected localities. The vertical component of ground motion is also presented, because it is essential for accurately assessing the response of short-period structures. Our methodology complements the more classic seismic hazard analyses, offering additional insights for earthquake contingency planning and loss analysis. The proposed methodology is flexible; multiple models and ongoing advancements in scenario practice (near-field effects, vertical ground motion, and the choice of ground motion models) can be easily incorporated, increasing the effectiveness of seismic scenario modeling in seismic emergency planning and risk mitigation.
For decades, scientists have probed Earth's remote mantle by analyzing how seismic waves of d... more For decades, scientists have probed Earth's remote mantle by analyzing how seismic waves of distant earthquakes pass through it. But we are still challenged by the technique's limitations.
In the brittle regime, faults tend to be oriented along an angle of about 30 °relative to the pri... more 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 criticalstress 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 preexisting 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.
Tidal forces are generally neglected in the discussion about the mechanisms driving plate tectoni... more 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 numerical 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 compatible with the slowing of the Earth's rotational spin. Our results suggest a westerly rotation of the lithosphere with a lower bound of x % ð0:1 À 0:2Þ /Myr in the presence of a basal effective shear viscosity g % 10 16 PaÁs, but it may rise to x > 1 /Myr with a viscosity of g K 3 Â 10 14 PaÁs 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 lateral viscosity heterogeneities at the base of the lithosphere, which determine variable lithosphereasthenosphere decoupling and plate interactions, hence plate tectonics.
Seismic prediction was considered impossible, however, there are no reasons in theoretical physic... more 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 perturbatio...
The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-last... more The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-lasting (early Miocene to Pleistocene) Na-alkali basaltic volcanism, sourced in the asthenosphere mantle. The upwelling asthenosphere at the Africa–Arabia margin produces very limited magma volumes in the axial zone. Therefore, portions of hot, fertile mantle continue their eastward migration and are stored at shallower depths under the 100-km thick Arabian lithosphere, which is much thinner than the African one (≈175 km): this causes the occurrence and 20-Ma persistence of magma supply under the study area. Erupted basalts sampled a continuous variation of the mantle source, with a striking correlation among temperature, pressure and isotopic composition shifting between two end members: a 100 km-deep, more depleted source, and a 60 km-deep, more enriched one. In particular, we observed an unusual variation in boron isotopes, which in the oceanic domain does not vary between more depleted a...
The processes occurring on the Earth are controlled by several gradients. The surface of the Plan... more 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 geodynamics 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 counterarguments 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 ...
Seismic prediction was considered impossible, however, there are no reasons in theoretical physic... more 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 perturbatio...
Abstract: The Plio-Pleistocene lava flows and domes of the Volos–Evia area were erupted between 3... more Abstract: The Plio-Pleistocene lava flows and domes of the Volos–Evia area were erupted between 3.4 and 0.5 Ma ago on the western continuation of the North Anatolian Fault, in a back-arc position with respect to the active arc. They are mainly high-K calc-alkaline trachyandesites. Based on their Sr–Nd–Pb isotopic compositions, the mantle source of the Volos–Evia area lavas is similar to that of a large volcanic belt that developed north of the Pelagonian–Attic–Cycladic–Menderes massifs, encompassing a 35 Ma timespan and ...
ABSTRACT We discuss the mechanics of crustal normal fault-related earthquakes, and show that they... more ABSTRACT We discuss the mechanics of crustal normal fault-related earthquakes, and show that they represent dissipation of gravitational potential energy (graviquakes) and their magnitude increases with the involved volume (delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall), and the fault dip. The magnitude increases with the deepening of the brittle–ductile transition (BDT), which in turn enlarges the involved volume. The fault dip seems rather controlled by the static friction of the involved crustal layers. We apply the model to the extensional area of the Italian peninsula, whose geodynamics is controlled by the Alpine and Apennines subduction zones. The latter has a well-developed backarc basin and a large part of the accretionary prism is affected by on-going extensional tectonics, which is responsible for most of peninsular Italy seismicity. Analyzing the seismic record of the Apennines, the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth. We compile a map of the brittle–ductile transition depth and, assuming a fixed 45° or 60° fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane, we compute the maximum volume of the hangingwall collapsing at the coseismic stage, and estimate the maximum expected magnitude. Lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow. Moreover, lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values.
The occurrence of Middle Triassic extensional and strike-slip tectonics has been widely recognize... more The occurrence of Middle Triassic extensional and strike-slip tectonics has been widely recognized in the Dolomites and is supported by stratigraphic evidence. Contrarily, the recognition of Triassic contractional tectonic structures is less straightforward because such structures were heavily superimposed by Neogene Alpine shortening. In this work we provide a detailed analysis of a top-class outcrop displaying a syn-sedimentary Middle Triassic extensional fault that displaces a coeval sedimentary mélange containing an olistholith of Lower Triassic rocks, characterized by Triassic contractional structures (folds, axial plane cleavage, joints, local thrust faults ornamented with slickenfibers and associated with forced folds). In particular, integrating geological field mapping and structural analyses, structural analyses on a 3D virtual outcrop model and microstructural analyses, we demonstrate that: 1) the orientation of tectonic structures in the olistholith is at odd with that of regional structures, implying that deformation occurred prior to deposition of the melange; 2) folds and small-scale thrusts in the olistholith developed in lithified rocks, pointing to the existence of Middle Triassic fold and thrust tectonics. In summary, the tectonic structures in the analyzed olistholith represent an outstanding, possibly unique, example of fully preserved, practically frozen, Middle Triassic contractional structures.
The processes occurring on the Earth are controlled by several gradients. The surface of the Plan... more 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 geodynamics 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 counterarguments 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.
The polyphase structural evolution of a sector of the internal Central Apennines, where the signi... more The polyphase structural evolution of a sector of the internal Central Apennines, where the significance of pelagic deposits atop neritic carbonate platform and active margin sediments has been long debated, is here documented. The results of a new geological survey in the Volsci Range, supported by new stratigraphic constraints from the syn-orogenic deposits, are integrated with the analysis of 2D seismic reflection lines and available wells in the adjacent Latin Valley. Late Cretaceous syn-sedimentary faults are documented and interpreted as steps linking a carbonate platform to the adjacent pelagic basin, located to the west. During Tortonian time, the pelagic deposits were squeezed off and juxtaposed as mélange units on top of the carbonate platform. Subsurface data highlighted stacked thrust sheets that were first involved into an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We distinguish up to four gro...
Shallow crustal faults are passive features mobilized by the dissipation of the potential energy ... more Shallow crustal faults are passive features mobilized by the dissipation of the potential energy and the shear stress accumulated in the brittle volume surrounding them. However, the stored energy in the volume differs from the tectonic setting, i.e., it is mainly gravitational in extensional tectonic settings, whereas it is elastic in strike-slip and contractional tectonic environments. In extensional settings, below about 1 km, the horizontal tensile stress is overwhelmed by the confining pressure of the lithostatic load, and it becomes positive, i.e. compressive. Therefore, there is no horizontal tension in extensional tectonic settings and the pro-gravity motion of the crustal volume is provided by the lithostatic load, which is the vertical maximum principal stress. The elastic energy is rather accumulated by the maximum horizontal principal stresses, i.e., iso-gravity in transcurrent settings and counter-gravity in contractional tectonic settings. The different relation with the gravitational force in the different tectonic settings generates several relevant differences in the three main tectonic environments. The extensional tectonic settings, both in continental and oceanic rift zones generate normal fault-related earthquakes, i.e., pro-gravity movements, or graviquakes. They differ from the other tectonic setting because are marked by (i) lower energy and lower differential stress to activate faults with respect to strike-slip and contractional tectonics; (ii) lower maximum earthquake magnitude; (iii) a larger number of low magnitude earthquakes in extensional settings because the crust moves downward as soon as it can move, whereas contractional settings require larger accumulation of energy to move counter-gravity; (iv) consequently, the b-value of the Gutenberg-Richter is higher than 1 and the aftershocks are more numerous and last longer in extensional settings; (v) the downward motion of the hangingwall determines more diffuse cataclastic deformation with respect to the other tectonic settings because the lithostatic load works everywhere, whereas in the other tectonic settings is concentrated where the elastic energy accumulates; (vi) in extensional settings the volume dimension is determined by thickness of the brittle layer, and its length is in average three times the seismogenic thickness; in strike-slip and contractional settings dominates the elastic energy (elastoquakes), and the mobilized volume may be ten to thirty times longer in a single seismic sequence, being its size proportional both to the brittle thickness and the relative speed of plates. These differences characterize the seismic cycle of graviquakes with respect to the elastoquakes. The bigger the volume, the wider the seismogenic fault in all tectonic settings. The interplay between the horizontal tectonic forces and the lithostatic load, which is ubiquitous, varies in the three main tectonic settings, generating different seismotectonic styles and an increase of magnitude as the effect of the vertical gravitational force becomes a minority relative to the elastic storage and coseismic rebound.
Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of ... more Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of seismology, their occurrence has been identified as a possible mechanism leading to further crustal destabilization, hence, to major failures. However, several cases occurred without any previous anomalous seismic activity, so that the hypothesis of foreshocks as reliable seismic precursors fails to pass statistical tests. Here, we perform an all-round statistical comparative analysis of seismicity in Southern California to assess whether any differences can be identified between swarms and foreshocks. Our results suggest that extremely variable seismic patterns can forerun mainshocks, even though they tend to be preceded by clusters with more numerous events spread over larger areas than swarms and with a wider range of magnitudes. We provide a physical explanation of such dissimilarity and conclude, despite it, that foreshocks can hardly be reliable shortterm precursors of large earthquakes in California. Plain Language Summary Large earthquakes can be preceded by a wide range of different seismic anomalies. Among these, seismicity has been reported to increase both in magnitude and frequency, but, on the other hand, it can also undergo a short period of reduced intensity before major events. The first pattern corresponds to the occurrence of foreshocks, that is, small to moderate quakes forewarning an upcoming larger one, while the second behavior is called seismic quiescence. In our research, we focus on foreshock activity. We perform an analysis of seismicity in Southern California, for which a well-provided relocated earthquake catalog is available. While several studies have been conducted so far about what happens before large earthquakes after their occurrence and also there are some works about foreshocks discrimination, a systematic analysis comparing properties of clusters of "swarms", seismicity without a major event, and "foreshocks" before their mainshock is missing. Are foreshocks different from swarms before the occurrence of the main event? Are foreshocks fore-shocks? Our results suggest that foreshocks can hardly be distinguished from swarms until the largest event takes place. On the base of this analysis and theoretical modeling, we think that foreshocks have limited reliability, if considered alone, for short-term forecasts.
The stretching of the lithosphere leading to back-arc basins formation generally develops behind ... more The stretching of the lithosphere leading to back-arc basins formation generally develops behind arctrench systems and is considered the consequence of slab retreat relative to the upper plate. Here, we examine the deformation regime evolution within the overriding plate due to subduction processes, using thermo-mechanical numerical simulations. We explore the northeastern Eurasia plate boundary and the mechanisms of subducting Pacific plate since 57 Ma. During this time interval, several extensional basins formed along the Eurasia margin, such as the East China Sea, the Japan Sea, and the Kuril basin. Here, we increased the simulation complexity, with the inclusion of (i) the kinematic variability of the Pacific plate over the geological past with respect to a fixed Eurasia, incorporating time-dependent (i.e., temporally evolving) velocities computed from plate motion reconstructions; (ii) a Low-Velocity Zone within the asthenosphere, and (iii) a horizontal eastward mantle flow. Our results show a crucial role of the mantle flow for the development of lithospheric extension and back-arc basin opening, and a main kinematic control of the subduction trench position, which advances and retreats, into distance intervals in the order of ∼ 100 km, and providing stages of compression and extension in a back-arc basin.
We propose an innovative methodology for seismic emergency planning and earthquake risk mitigatio... more We propose an innovative methodology for seismic emergency planning and earthquake risk mitigation in central Italy by integrating three prototypal earthquake scenarios. The different scenarios derive maximum earthquake magnitudes from different input data. The first scenario utilizes local rheological, geological, and geophysical conditions; the second scenario considers the study area fault characteristics, while the third scenario relies on the cluster analysis of historical and instrumental earthquake records. The magnitudes and related uncertainties are combined using a conflation method to derive the expected ground motions for a grid of sites in central Italy. The resulting scenarios include peak ground acceleration and spectral ordinates, presented as maps and spectra for two selected localities. The vertical component of ground motion is also presented, because it is essential for accurately assessing the response of short-period structures. Our methodology complements the more classic seismic hazard analyses, offering additional insights for earthquake contingency planning and loss analysis. The proposed methodology is flexible; multiple models and ongoing advancements in scenario practice (near-field effects, vertical ground motion, and the choice of ground motion models) can be easily incorporated, increasing the effectiveness of seismic scenario modeling in seismic emergency planning and risk mitigation.
For decades, scientists have probed Earth's remote mantle by analyzing how seismic waves of d... more For decades, scientists have probed Earth's remote mantle by analyzing how seismic waves of distant earthquakes pass through it. But we are still challenged by the technique's limitations.
In the brittle regime, faults tend to be oriented along an angle of about 30 °relative to the pri... more 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 criticalstress 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 preexisting 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.
Tidal forces are generally neglected in the discussion about the mechanisms driving plate tectoni... more 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 numerical 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 compatible with the slowing of the Earth's rotational spin. Our results suggest a westerly rotation of the lithosphere with a lower bound of x % ð0:1 À 0:2Þ /Myr in the presence of a basal effective shear viscosity g % 10 16 PaÁs, but it may rise to x > 1 /Myr with a viscosity of g K 3 Â 10 14 PaÁs 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 lateral viscosity heterogeneities at the base of the lithosphere, which determine variable lithosphereasthenosphere decoupling and plate interactions, hence plate tectonics.
Seismic prediction was considered impossible, however, there are no reasons in theoretical physic... more 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 perturbatio...
The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-last... more The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-lasting (early Miocene to Pleistocene) Na-alkali basaltic volcanism, sourced in the asthenosphere mantle. The upwelling asthenosphere at the Africa–Arabia margin produces very limited magma volumes in the axial zone. Therefore, portions of hot, fertile mantle continue their eastward migration and are stored at shallower depths under the 100-km thick Arabian lithosphere, which is much thinner than the African one (≈175 km): this causes the occurrence and 20-Ma persistence of magma supply under the study area. Erupted basalts sampled a continuous variation of the mantle source, with a striking correlation among temperature, pressure and isotopic composition shifting between two end members: a 100 km-deep, more depleted source, and a 60 km-deep, more enriched one. In particular, we observed an unusual variation in boron isotopes, which in the oceanic domain does not vary between more depleted a...
The processes occurring on the Earth are controlled by several gradients. The surface of the Plan... more 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 geodynamics 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 counterarguments 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 ...
Seismic prediction was considered impossible, however, there are no reasons in theoretical physic... more 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 perturbatio...
Abstract: The Plio-Pleistocene lava flows and domes of the Volos–Evia area were erupted between 3... more Abstract: The Plio-Pleistocene lava flows and domes of the Volos–Evia area were erupted between 3.4 and 0.5 Ma ago on the western continuation of the North Anatolian Fault, in a back-arc position with respect to the active arc. They are mainly high-K calc-alkaline trachyandesites. Based on their Sr–Nd–Pb isotopic compositions, the mantle source of the Volos–Evia area lavas is similar to that of a large volcanic belt that developed north of the Pelagonian–Attic–Cycladic–Menderes massifs, encompassing a 35 Ma timespan and ...
ABSTRACT We discuss the mechanics of crustal normal fault-related earthquakes, and show that they... more ABSTRACT We discuss the mechanics of crustal normal fault-related earthquakes, and show that they represent dissipation of gravitational potential energy (graviquakes) and their magnitude increases with the involved volume (delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall), and the fault dip. The magnitude increases with the deepening of the brittle–ductile transition (BDT), which in turn enlarges the involved volume. The fault dip seems rather controlled by the static friction of the involved crustal layers. We apply the model to the extensional area of the Italian peninsula, whose geodynamics is controlled by the Alpine and Apennines subduction zones. The latter has a well-developed backarc basin and a large part of the accretionary prism is affected by on-going extensional tectonics, which is responsible for most of peninsular Italy seismicity. Analyzing the seismic record of the Apennines, the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth. We compile a map of the brittle–ductile transition depth and, assuming a fixed 45° or 60° fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane, we compute the maximum volume of the hangingwall collapsing at the coseismic stage, and estimate the maximum expected magnitude. Lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow. Moreover, lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values.
The occurrence of Middle Triassic extensional and strike-slip tectonics has been widely recognize... more The occurrence of Middle Triassic extensional and strike-slip tectonics has been widely recognized in the Dolomites and is supported by stratigraphic evidence. Contrarily, the recognition of Triassic contractional tectonic structures is less straightforward because such structures were heavily superimposed by Neogene Alpine shortening. In this work we provide a detailed analysis of a top-class outcrop displaying a syn-sedimentary Middle Triassic extensional fault that displaces a coeval sedimentary mélange containing an olistholith of Lower Triassic rocks, characterized by Triassic contractional structures (folds, axial plane cleavage, joints, local thrust faults ornamented with slickenfibers and associated with forced folds). In particular, integrating geological field mapping and structural analyses, structural analyses on a 3D virtual outcrop model and microstructural analyses, we demonstrate that: 1) the orientation of tectonic structures in the olistholith is at odd with that of regional structures, implying that deformation occurred prior to deposition of the melange; 2) folds and small-scale thrusts in the olistholith developed in lithified rocks, pointing to the existence of Middle Triassic fold and thrust tectonics. In summary, the tectonic structures in the analyzed olistholith represent an outstanding, possibly unique, example of fully preserved, practically frozen, Middle Triassic contractional structures.
The processes occurring on the Earth are controlled by several gradients. The surface of the Plan... more 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 geodynamics 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 counterarguments 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.
The polyphase structural evolution of a sector of the internal Central Apennines, where the signi... more The polyphase structural evolution of a sector of the internal Central Apennines, where the significance of pelagic deposits atop neritic carbonate platform and active margin sediments has been long debated, is here documented. The results of a new geological survey in the Volsci Range, supported by new stratigraphic constraints from the syn-orogenic deposits, are integrated with the analysis of 2D seismic reflection lines and available wells in the adjacent Latin Valley. Late Cretaceous syn-sedimentary faults are documented and interpreted as steps linking a carbonate platform to the adjacent pelagic basin, located to the west. During Tortonian time, the pelagic deposits were squeezed off and juxtaposed as mélange units on top of the carbonate platform. Subsurface data highlighted stacked thrust sheets that were first involved into an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We distinguish up to four gro...
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Papers by Carlo Doglioni