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De Martino, Salvatore
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- PublicationOpen AccessThe Long-Period seismicity before and during the volcanic crises: examples from two case studies(2015-02-23)
; ; ; ; ; ;Palo, Mauro; GeoForschungsZentrum, Germany ;De Martino, Salvatore; University of Salerno ;Falanga, Mariarosaria; University of Salerno ;Cusano, Paola; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;West, Michael E.; University of Alaska Fairbanks, United States; ; ; ; The Long-Period (LP) seismicity is common at active volcanoes and is usually modeled as due to pressurized magmatic fluids flowing through rock cavities. These signals are sensitive to the thermodynamic conditions of the magma-gas mixture in the shallow plumbing system and can thus be adopted as “detectors” of an impelling eruption. We found that at Stromboli (Italy) before and/or during recent volcanic crises the LP events can occur in swarms, which show different statistics, higher energy and shallower location than the stationary LP activity. We imputed the LP swarms to a quick depressurization (|ΔP|≥105 Pa) of the shallowest (<0.8 km) part of the conduit. At Shishaldin (Alaska) the 2004 eruption is anticipated by a migration towards the surface of the LP source, which moves from ~8 km to ≾5 km below the crater rim. By simple assumptions, we modeled this source change as produced by an increase of the confining pressure within the plumbing system of ~5x107 Pa, possibly induced by an upward migration of ~108-1010 kg of magma.241 129 - PublicationOpen AccessRadon migration in the soils of the Irno Valley (Southern Italy) inferred from radioactive disequilibrium(1995-09)
; ; ; ;De Martino, S.; Dipartimento di Fisica, Università di Salerno, Baronissi, Salerno, Italy ;Sabbarese, C.; Dipartimento di Geofisica e Vulcanologia, Università di Napoli "Federico II", Napoli, Italy ;Gasparini, P.; Dipartimento di Geofisica e Vulcanologia, Università di Napoli "Federico II", Napoli, Italy; ; Radon migration along vertical profiles in the soils of Irno River alluvial Valley (Southern Italy) was studied using radioactive disequilibrium between 226 Ra and 210 Pb. Fractional Radon loss, migration length, diffusion and emanation coefficient and Radon flux density were determined. Our results are in agreement with a migra- tion model by simple diffusion. The migration parameters are within typical values, except the Radon flux density, which is about one order of magnitude higher than the values reported in literature. The values of fractional Radon loss are sensitive to changes in the physical properties of the soil.186 235 - PublicationRestrictedSelf-sustained oscillations at Volcan de Colima (Mexico) inferred by Independent Component Analysis(2011-01-12)
; ; ; ; ;De Lauro, E.; Univ. of Salerno ;De Martino, S.; Univ. of Salerno ;Palo, M.; Univ. of Salerno ;Ibanez, M. J.; Univ. of Granada; ; ; We have analyzed Long-Period (LP) seismic events of Volcan de Colima (Mexico) recorded by four three-component broad-band seismometers during January 2006. Frequency-domain analysis shows broad-band spectra mainly in the range 0.3-2 Hz characterized by a monotonic decreasing envelope, as those observed in a cylindrically-symmetric self-oscillating cavity interacting with a confined jet. Independent Component Analysis, a time decomposition method extracts two or three nonlinear oscillation modes depending on the station, with the fundamental one peaked at [0.4-0.5]Hz. These decomposed waves are self-sustained oscillations with low dimensionality and a well defined spectral content. Moreover, they show radial polarization in near field and transverse polarization in far field in North-West South-East direction. Finally, we depict a branched plumbing system with two principal conduits directed along orthogonal directions.331 45 - PublicationRestrictedFast wavefield decomposition of volcano-tectonic earthquakes into polarized P and S waves by Independent Component AnalysisIn the present work a new approach for the analysis of polarization of seismic signals is proposed. The method is based on Independent Component Analysis and allows the identification and separation of the basic sources, which are naturally polarized into the vertical and horizontal planes. The results from the case study of a swarm of volcano-tectonic earthquakes occurred at Campi Flegrei in October 2015 are impressive: a clear separation of the P- and S-wave seismic phases in the time domain is obtained. In addition, the efficiency of the method in retrieving the polarization parameters is demonstrated by the comparison with other standard techniques. The presented approach provides wavefield decomposition and polarization analysis in a single step, thus avoiding a priori cumbersome filtering procedures and segmentation of the signals. It is useful for discriminating and analysing different seismic phases and can be applied to a variety of volcanic and tectonic signals, therefore it can strongly support all the studies on propagation and source mechanism. Moreover, due to its fastness and robustness this stand-alone tool can be routinely used in the volcano monitoring practice.
149 38 - PublicationOpen AccessStatistical analysis of the volcano seismicity during the 2007 crisis of Stromboli, Italy: a 3-day oscillatory signal as onset of the activity(2011)
; ; ; ; ; ;De Martino, Salvatore; University of Salerno ;Falanga, Mariarosaria; University of Salerno ;Palo, Mauro; University of Salerno ;Montalto, Placido; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Patanè, Domenico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; ; We analyze the volcano seismicity recorded during the 2007 eruption of Stromboli. Data-set is composed of the continuous recordings of a three-component broad-band seismometer and of a strainmeter. Starting from the characterization of the standard activity as a stationary phase of equilibrium, we investigate the non-equilibrium phase of the effusive process. A statistical analysis of the explosions reveals that the occurrence is always driven by a Poisson process as for the standard activity, even approaching the effusion phase, with the only difference in shortening the inter-times just during the effusion. A slightly different process can be advocated for the swarms of the explosions, because a maximum in the distribution of inter-times can be evidenced. Regarding the amplitudes of the explosion-quakes, they have a log-normal distribution until the effusion onset as in the standard Strombolian activity. The actual departure from that stationarity seems to be traced by an early deformative response at very long period. It appears as a transient oscillating signal characterized by a period of about three days that modulates the explosion amplitudes. In a conceptual organ pipe-like model it is related to the chocking of the pipe. The successive activity can be interpreted as the response of volcano to restore the equilibrium condition.462 184 - PublicationRestrictedStatistical analysis of the volcano seismicity during the 2007 crisis(2011)
; ; ; ; ; ;De Martino, S.; Dipartimento di Ingegneria Industriale, Università di Salerno, Fisciano, Italy ;Falanga, M.; Dipartimento di Ingegneria Industriale, Università di Salerno, Fisciano, Italy ;Palo, P.; Dipartimento di Ingegneria Industriale, Università di Salerno, Fisciano, Italy ;Montalto, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Patanè, Domenico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; ; We analyze the volcano seismicity recorded during the pre‐ and co‐eruptive regimes of the 2007 effusive crisis at Stromboli volcano (Italy). Data‐set is composed of the continuous recordings of a three‐component broad‐band seismometer and of a Sacks‐ Evertson strainmeter. Starting from the characterization of the non effusive phase as a stationary state of equilibrium, we investigate the effusive phase as a non‐equilibrium state. A statistical analysis reveals that the explosion occurrence is always driven by a nearly Poissonian process, as for the standard activity, even during the effusive phase, with the only difference in shortening the inter‐times. Explosion‐quake amplitudes are lognormally distributed until the effusive phase, becoming then broader. This indicates that many scales are involved. A slightly different process can be advocated for the swarms of the explosions occurring during the effusive phase. This suggests that the dynamics of the exsolution and/or aggregation of the gas slugs should differ from the nucleation mechanism responsible of the standard Strombolian activity. The pre‐eruptive regime is characterized by a very long deformative signal that appears as a transient oscillating signal with a period of about three days that modulates the explosion amplitudes. In a conceptual vibrating cavities model, it is related to a chocking phenomenon induced by magma injection, which in turn leads to the effusion.218 15 - PublicationRestrictedModel for high-frequency Strombolian tremor inferred by wavefield decomposition andreconstruction of asymptotic dynamics(2008)
; ; ; ; ; ; ;De Lauro, E.; Dipartimento di Matematica e Informatica, Universita` degli Studi di ;De Martino, S.; Dipartimento di Matematica e Informatica, Universita` degli Studi di ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Falanga, M. R.; Dipartimento di Matematica e Informatica, Universita` degli Studi di ;Paolo, M.; Dipartimento di Matematica e Informatica, Universita` degli Studi di ;Scarpa, R.; Dipartimento di Matematica e Informatica, Universita` degli Studi di; ; ; ; ; We study the volcanic tremor time series recorded by a broadband three-component seismic network installed at Stromboli volcano during 1997. By using decomposition methods in both frequency and time domains, we prove that Strombolian tremor can be described as a linear combination of nonlinear signals in time domain. These ‘‘components’’ are similar to those obtained for explosion quakes, with the only difference being the amplitude enhancement. We characterize each of these nonlinear signals both in terms of their wavefield properties as well as dynamic systems. Moreover, we take into account the complex processes of magma flow and turbulent degassing, looking at time and amplitude modulation of tremor on a suitable scale. The distribution of tremor amplitudes is Gaussian while the intertimes between the maxima in a suitable scale are described by a Poisson clustered process. Starting from these analyses, a first approximate model for volcanic tremor field can be deduced. The recorded signals, i.e., the elastic vibrations at a point, can be described by a nonlinear equation which gives limit cycles (different observed ‘‘nonlinear modes’’). This equation is governed by a time-dependent threshold which represents the variability of bubble flux. We take into account some inelasticity in the medium perturbing the elastic potential with a Gaussian function on a suitable scale. It acts as a radiance function modulating the frequency of the limit cycle. This proposed model is able to reproduce waveform, Fourier spectrum, and phase space dimension of one of the extracted nonlinear wave packets.203 26 - PublicationRestrictedConvolutive independent component analysis for processing massive datasets: a case study at Campi Flegrei (Italy)A novel procedure is proposed to analyse continuous seismic signal on hourly scales to have a prompt discrimination among the different sources. Specifically, this approach is applied to a massive dataset recorded at Campi Flegrei caldera during the year 2006 when a swarm of volcano-tectonic earthquakes occurred. The convolutive independent component analysis is adopted to obtain a clear separation among meteo-marine microseism, anthropogenic noise, hydrothermal tremor in the absence of volcano-tectonic activity, whereas in non-stationary conditions a contribution connected to the corner frequency of the earthquakes emerges. A coarse-grained variable to be monitored continuously is introduced, i.e. the frequency associated with the maximum amplitude of the power spectral density of the deconvolutive independent components. That parameter is sensitive to the variation in the frequency bands of interest (e.g. that corresponding to the corner frequencies of volcano-tectonic events) and can be used as marker of the insurgence of seismic activity.
166 39 - PublicationRestrictedA statistical study of the Stromboli volcano explosion quakes before and during 2002-2003 eruptive crisis(2011-04)
; ; ; ;De Martino, S.; Dipartimento di Ingegneria Industriale, Università di Salerno, Fisciano, Italia ;Palo, M.; Dipartimento di Ingegneria Industriale, Università di Salerno, Fisciano, Italia ;Cimini, G. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; We study the seismic wavefield and the statistical properties of the Stromboli volcano explosions preceding and during the 2002–2003 crisis. We analyze the recordings of a three‐component seismometer operating since 23 May 2002 to 30 January 2003, including the first 34 days of the crisis. Before the crisis, we recognize three bell‐shaped classes of spectra with maxima falling in the range 1–5 Hz. Spectral content has two main changes, the most prominent one occurring at the crisis onset when the frequency peak at ∼0.3 Hz increases in amplitude. Independent component analysis extracts three time‐stable independent oscillations that peaked at 1.1, 1.8, and 2.5 Hz, with radial and shallow polarization indicating a stable source mechanism. Energy of the explosions is lognormally distributed, except during a 2 month time interval before the crisis when it also shows a higher mean value. The interoccurrence time distributions display an homogeneous Poissonian behavior with a mean intertime of 250 s, without changes at the crisis onset. Only swarms of explosions are not ruled by a Poisson process and display higher occurrence rates and higher energies. Finally, we depict a scheme of the crisis. A modification of the equilibrium is induced by rising magma that produces a change in the boundary conditions of the plumbing system. The escape from the equilibrium produces, at first, variations in the usual statistics of the explosions, then it leads to the lava effusion and to a pressure drop in the plumbing system that induces a deep gas slug nucleation and the excitation of low frequencies.138 16 - PublicationOpen AccessCharacterization of the seismic dynamical state through joint analysis of earthquakes and seismic noise: the example of Ischia Volcanic Island (Italy)(2020-04-09)
; ; ; ; ; ; ; ; ; This work is devoted to the study of both earthquakes and background seismic noise at Ischia Island (Italy) recorded pre and post the Md 4.0 earthquake occurred on 21 August 2017 (18:57 UTC). We compare and characterize noise and earthquakes in terms of Independent Component Analysis, energy and polarization properties. The earthquakes’ waveforms and the background noise are decomposed into a few independent components with two main common signals peaked around 1–2 and 3–4 Hz, respectively. A slight increase of the energy of the background seismic noise is observed comparing samples recorded in 2016 and 2017, whereas no variations are detected in 2017 pre and post the main earthquake. The polarization analysis, performed in the frequency bands individuated by Independent Component Analysis and applied to the background seismic noise, indicates a shallow propagation and the azimuthal pattern is mainly controlled by the local structural features. These results suggest that noise and earthquakes are ascribable to a common phenomenon of fluid-solid interaction in the hydrothermal system of Ischia Island.315 86