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Seconda Università degli Studi di Napoli
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- PublicationRestrictedParameter Estimation in the ETAS Model: Approximations and Novel Methods(2014)
; ; ; ; ; ;Lippiello, E.; Second University of Naples ;Giacco, F.; Second University of Naples ;De Arcangelis, L.; Second University of Naples ;Marzocchi, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Godano, C.; Second University of Naples; ; ; ; Branching processes provide an accurate description of earthquake occurrence in the short term (days to a few weeks). Yet, the implementation of these models is not usually straightforward because of the difficulties in estimating the parameters. Indeed, log-likelihood estimation involves a spatial integral that cannot be analytically evaluated and is difficult to implement in numerical codes. Here we present a novel technique that allows for an accurate, stable, and relatively fast param- eter inversion procedure. We study the efficiency of this technique using synthetic epidemic-type aftershock sequence catalogs with a set of parameters known a priori. Results show the efficiency of the novel technique and illustrate the limits of recently proposed approximations147 26 - PublicationRestrictedDistribution of volcanic earthquake recurrence intervals(2009)
; ; ; ;Bottiglieri, M.; Department of Environmental Sciences and CNISM, Second University of Naples, Caserta, Italy. ;Godano, C.; Department of Environmental Sciences and CNISM, Second University of Naples, Caserta, Italy. ;D’Auria, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; We analyze the distribution of volcanic earthquake recurrence intervals in the Vesuvio, Campi Flegrei, and Hawaii regions and compare it with tectonic recurrence rates in California. We find that the distribution behavior is similar for volcanic and tectonic seismic events. In both cases, the recurrence interval distributions collapse onto the same master curve if time is rescaled by the average occurrence rate. This implies that both phenomena have the same temporal organization, and it is possible to adopt for volcanic areas that the same occurrence models used for tectonic regions.149 31 - 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 - PublicationRestrictedStatistical Features of Foreshocks in Instrumental and ETAS Catalogs(2017)
; ; ; ; ; ; ; ; ; We study the spatial distribution of earthquakes in temporal intervals before and after the occurrence of large shocks (mainshocks) in the magnitude range m [2 5] for four different regional catalogs. We find that the spatial organization of pre-shock seismicity depends on the mainshock magnitude and is independent of the lower magnitude threshold. These properties are found to be a stable feature of regional catalogs and cannot be reproduced by Epidemic Type Aftershock Sequence models. Our findings suggest that the area fractured during the mainshock is encoded in the foreshock spatial organization and, therefore, enhance the prognostic value of foreshocks.50 4 - 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 6 - PublicationOpen AccessA detailed analysis of some local earthquakes at Somma-Vesuvius(1999-06)
; ; ; ; ; ; ;Capuano, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Coppa, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Natale, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Di Sena, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Godano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Troise, C.; Dipartimento di Geofisica e Vulcanologia, Università di Napoli "Federico II", Napoli, Italy; ; ; ; ; In this paper, we analyze local earthquakes which occurred at Somma-Vesuvius during two episodes of intense seismic swarms, in 1989 and 1995 respectively. For the selected earthquakes we have computed accurate hypocentral locations, focal mechanisms and spectral parameters. We have also studied the ground acceleration produced by the largest events of the sequences (ML 3.0), at various digital stations installed in the area during the periods of higher seismic activity. The main result is that seismicity during the two swarm episodes presents similar features in both locations and focal mechanisms. Strong site dependent effects are evidenced in the seismic radiation and strong amplifications in the frequency band 10-15 Hz are evident at stations located on the younger Vesuvius structure, with respect to one located on the ancient Somma structure. Furthermore, seismic stations show peak accelerations for the same events of more than one order of magnitude apart.197 361 - PublicationOpen AccessAn Automated Method for Mapping Independent Spatial b Values(2022)
; ; ; ; ; ; ; We present an automated method for mapping the b values. The algorithm is very simple and presents three advantages: (a) it does not requires any tuning of the parameters like, for instance, a fixed cell size or a maximum radius of the cell; (b) it implies a more appropriate use of the catalog, by using almost all the events in the catalog used (with a tolerance of 1%) with no overlap; (c) it implies the full independence of the b values, thus allowing the statistical comparison of the results using standard tests. Although the resulting b values are comparable with those obtained by applying the other methods of common use in seismology, these latter (a) leave out many earthquakes from the analysis, with loose of useful information, (b) produce diffuse cells overlapping aiming at reaching many cells of the grid in order to get the correct number of events in each cell, and (c) results in correlated b values, which do not allow the test of significance for the differences in the b values. Finally, due to the independence from any ad hoc a-priori choice, our method is suitable for automatic and operator-free procedures.228 105 - 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 - PublicationRestrictedIndependent component analysis as a tool for ground deformation analysis(2007)
; ; ; ; ; ; ; ;Bottiglieri, M.; Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italy ;Falanga, M.; Dipartimento di Fisica, Università di Salerno, Baronissi (SA), Italy ;Tammaro, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Obrizzo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Martino, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Godano, C.; Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italy ;Pingue, 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.297 32
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