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Seconda Università degli Studi di Napoli
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- PublicationOpen AccessANALISI DELLE COMPONENTI INDIPENDETI (ICA) NELLO STUDIO DELLE DEFORMAZIONI DEL SUOLO IN AREE VULCANICHE(2007-11-06)
; ; ; ; ; ; ; ;Godano, C.; Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italia. ;Pingue, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bottiglieri, M.; Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italia. ;Falanga, M.; Dipartimento di Fisica, Università di Salerno, Baronissi (SA), Italia. ;Tamarro, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Martino, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Obrizzo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; ; ; Independent component analysis (ICA) is a recent and well-known technique used to separate mixtures of signals. This technique has been applied to the ground deformation time-series recorded at the permanent GPS network of the Osservatorio Vesuviano-INGV in order to characterize the deformation background level in the Neapolitan volcanic area. The analysis revealed the presence of five independent periodic signals common at all the GPS stations; some of them are interpreted as effects of earth tides. The residual signal at each station represent the local ground deformation. Unfortunately the ICA cannot provide the absolute amplitude of the components, indeed we are not able to obtain a residual amplitude at each station. Then we used a stationarity analysis in order to investigate the eventual presence of local transient deformations. The ICA technique combined with the stationarity analysis has shown to be a very interesting tool for individuating ground deformation trends and could be very useful in volcanic areas monitoring.198 530 - PublicationOpen AccessNonlinear convective motion of the asthenosphere and the lithosphere melting: a model for the birth of a volcanoThe processes of heat transfer occurring between the Earth’s asthenosphere and lithosphere are responsible for partial melting of rocks, leading to the magma generation and its migration and segregation in the crust and, possibly, to volcanoes generation at the surface. Convection is the dominant mechanism regulating the heat transfer from the asthenosphere to the lithosphere, although many aspects of the whole process are not yet clear. Therefore, the knowledge of the physical processes leading to the melting of the lithospheric rocks has important consequences in understanding the interior Earth dynamics, the surface volcanic dynamics, and its related hazards. Rock melting occurs when the temperature gradient meets the rock solidus. Here, we propose a nonlinear convective 1D analytical model (representing an approximation of more 3D complex models). The steady-state solution of our equation is in good agreement with the estimated geotherms of the asthenosphere. A perturbative approach leads to a heat swelling at the boundary between asthenosphere and lithosphere able to determine its melting and the birth of a volcano.
134 7 - PublicationRestrictedHow Long is an Aftershock Sequence?The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue.
119 1 - PublicationOpen AccessThe Dependence on the Moho Depth of the b-Value of the Gutenberg–Richter Law(2022)
; ; ; ; ; ; ; ;; We investigate the dependence of the Gutenberg–Richter b parameter on the crustal thickness quantified by the Moho depth, for nine different regional catalogs. We find that, for all the catalogs considered in our study, the b‐value is larger in areas presenting a thicker crust. This result appears in apparent contradiction with previous findings of a b decreasing with the focal depth. However, both the results are consistent with acoustic emission experiments, indicating a b‐value inversely proportion to the applied differential stress. Our results can be indeed interpreted as the signature of a larger stress concentration in areas presenting a thinner crust. This is compatible with the scenario where postseismic deformation plays a central role in stress concentration and in aftershock triggering.223 131 - PublicationOpen AccessThe Signal to Noise Ratio and the Completeness Magnitude: The Effect of the COVID-19 Lockdown(2021)
; ; ; ; ; We analyse the earthquakes catalogues for Italy, South California, and Greece across the COVID-19 lockdown period for each country. The results for Italy and Greece show that, even if the reduction of the signal to noise ratio has improved the earthquake detection capability, the completeness magnitude remains substantially unchanged, making the improved detection capability ineffective from the statistical point of view. A slight reduction (0.2) of the completeness magnitude is observed for South California, likely related to the relatively higher number of seismic stations located close to urban areas. Our findings suggest that—given the present configuration of the seismic network considered here—only an important decrease in the station spacing can produce a significant decrease of the completeness magnitude.215 9 - PublicationOpen AccessForecasting of the first hour aftershocks by means of the perceived magnitudeThe majority of strong earthquakes takes place a few hours after a mainshock, promoting the interest for a real time post-seismic forecasting, which is, however, very inefficient because of the incompleteness of available catalogs. Here we present a novel method that uses, as only information, the ground velocity recorded during the first 30 min after the mainshock and does not require that signals are transferred and elaborated by operational units. The method considers the logarithm of the mainshock ground velocity, its peak value defined as the perceived magnitude and the subsequent temporal decay. We conduct a forecast test on the nine M ≥ 6 mainshocks that have occurred since 2013 in the Aegean area. We are able to forecast the number of aftershocks recorded during the first 3 days after each mainshock with an accuracy smaller than 18% in all cases but one with an accuracy of 36%.
228 26 - PublicationRestrictedMechanical origin of aftershocks(2015)
; ; ; ; ; ; ; ; ; Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the in influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering.69 1 - PublicationOpen AccessLooking inside mt. vesuvius(1998)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Italy's Mt.Vesuvius has been slumbering for a long time, but its silence could preface an eruption with potentially disastrous effects for 600,000 people living on the volcano's slopes. To assess the scenario of the next eruption, the National Group of Vol-canology (GNV) of the Italian National Council of Researches (CNR) has fostered research aimed at mitigating eruption risk to the densely populated area. In this framework, researchers have gathered high-resolution seismic tomography data to better understand the internal structure of Mt. Vesuvius. The experiments were carried out during the last 4 years. The data will be used in three-dimensional modeling of the structure of Mt. Vesuvius and underlying upper crust. Seismic velocities and attenuation and density contrasts will be calculated, with special emphasis on the delineation of significant magma reservoirs of more than 1 km in diameter. In modeling Mt. Vesuvius, tools are being developed for using seismogram information to obtain high-quality seismic imaging of heterogeneous structures such as volcanoes221 33 - PublicationOpen AccessEvaluation of the b Maps on the Faults of the Major (M > 7) South California Earthquakes(2024)
; ; ; ; ; We use the Godano et al. (2022, https://doi.org/10.1029/2021ea002205) method for evaluating the b maps of the faults associated with the largest earthquakes M ≥ 7.0 that occurred in California. The method allows an independent evaluation of the b parameter, avoiding the overlap of the cells and the omission of some earthquakes, while keeping all the available information in the catalog. We analyzed four large earthquakes: Landers, Hector Mine, Baja California, and Searles Valley. The maps obtained confirm that the b value can be considered as a strain meter and allow us to elucidate the presence of barriers, such as obstacles to the propagation of the fracture, on the fault of the analyzed earthquakes. A further estimated parameter is the time window during which aftershocks occur in the cell, Δt. This quantity is very useful for a better definition of the aftershock generation mechanism. It reveals where the stress is released in a short time interval and how the complexity of the faulting process controls the occurrence of aftershocks on the fault, and also the duration of the entire sequence.25 2 - PublicationOpen AccessSubduction age and stress state control on seismicity in the NW Pacific subducting plate(2022)
; ; ; ; ; ; ; Intermediate depth (70-300 km) and deep (>300 km) earthquakes have always been puzzling Earth scientists: their occurrence is a paradox, since the ductile behavior of rocks and the high confining pressure with increasing depths would theoretically preclude brittle failure and frictional sliding. The mechanisms proposed to explain deep earthquakes, mainly depending on the subducting plate age and stress state, are generally expressed by single parameters, unsuitable to comprehensively account for differences among distinct subduction zones or within the same slab. We analyze the Kurile and Izu-Bonin intraslab seismicity and detail the stress state along the subducted planes using the Gutenberg-Richter b-value. We demonstrate that, despite the slabs different properties (e.g., lithospheric age, stress state, dehydration rate), in both cases deep earthquakes are restricted to depths characterized by equal age from subduction initiation and are driven by stress regimes affected by the persistence of the metastable olivine wedge.320 5
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