1,721,199 research outputs found
Attenuation and velocity structure in the area of Pozzuoli-Solfatara (Campi Flegrei, Italy) for the estimate of local site response
No full textIn the present work I infer the 1D shear-wave velocity model in the volcanic area of Pozzuoli-Solfatara using the dispersion properties of both Rayleigh waves generated by artificial explosions and microtremor. The group-velocity dispersion curves are retrieved from application of the Multiple Filter Technique (MFT) to single-station recordings of air-gun sea shots. Seismic signals are filtered in different frequency bands and the dispersion curves are obtained by evaluating the arrival times of the envelope maxima of the filtered signals. Fundamental and higher modes are carefully recognized and separated by using a Phase Matched Filter (PMF). The obtained dispersion curves indicate Rayleigh-wave fundamental-mode group velocities ranging from about 0.8 to 0.6 km/sec over the 1-12 Hz frequency band.
I also propose a new approach based on the autoregressive analysis, to recover group velocity dispersion. I first present a numerical example on a synthetic test signal and then I apply the technique to the data recorded in Solfatara, in order to compare the obtained results with those inferred from the MF analysis
Moreover, I analyse ambient noise data recorded at a dense array, by using Aki’s correlation technique (SAC) and an extended version of this method (ESAC) The obtained phase velocities range from 1.5 km/s to 0.3 km/s over the 1-10 Hz frequency band.
The group velocity dispersion curves are then inverted to infer a shallow shear-wave velocity model down to a depth of about 250 m, for the area of Pozzuoli-Solfatara. The shear-wave velocities thus obtained are compatible with those derived both from cross- and down-hole measurements in neighbour wells and from laboratory experiments. These data are eventually interpreted in the light of the geological setting of the area.
I perform an attenuation study on array recordings of the signals generated by the shots. The attenuation curve was retrieved by analysing the amplitude spectral decay of Rayleigh waves with the distance, in different frequency bands. The attenuation curve was then inverted to infer the shallow Q inverse model.
Using the obtained velocity and attenuation model, I calculate the theoretical ground response to a vertically-incident SH-wave obtaining two main amplification peaks centered at frequencies of 2.1 and 5.4 Hz. The transfer function was compared with that obtained experimentally from the application of Nakamura’s technique to microtremor data, artificial explosions and local earthquakes. Agreement between the two transfer functions is observed only for the amplification peak of frequency 5.4 Hz.
Finally, as a complementary contribution that might be used to the assessment of seismic risk in the investigated area, I evaluate the peak ground acceleration (PGA) for the whole Campi Flegrei caldera and locally for the Pozzuoli-Solfatara area, by performing stochastic simulation of ground motion partially constrained by the previously described results. Two different methods (Random Vibration Theory (RVT) and ground motion generated from a Gaussian distribution (GMG)) are used, providing the PGA values of 0.04 g and 0.097 g for Campi Flegrei and Pozzuoli-Solfatara, respectively
Tidal synchronization of Long Period (LP) events and hydrothermal tremor at Campi Flegrei (Italy)
No full textAttenuation and velocity structure in the area of Pozzuoli-Solfatara (Campi Flegrei, Italy) for the estimate of local site response
No full textIn the present work I infer the 1D shear-wave velocity model in the volcanic area of Pozzuoli-Solfatara using the dispersion properties of both Rayleigh waves generated by artificial explosions and microtremor. The group-velocity dispersion curves are retrieved from application of the Multiple Filter Technique (MFT) to single-station recordings of air-gun sea shots. Seismic signals are filtered in different frequency bands and the dispersion curves are obtained by evaluating the arrival times of the envelope maxima of the filtered signals. Fundamental and higher modes are carefully recognized and separated by using a Phase Matched Filter (PMF). The obtained dispersion curves indicate Rayleigh-wave fundamental-mode group velocities ranging from about 0.8 to 0.6 km/sec over the 1-12 Hz frequency band.
I also propose a new approach based on the autoregressive analysis, to recover group velocity dispersion. I first present a numerical example on a synthetic test signal and then I apply the technique to the data recorded in Solfatara, in order to compare the obtained results with those inferred from the MF analysis
Moreover, I analyse ambient noise data recorded at a dense array, by using Aki’s correlation technique (SAC) and an extended version of this method (ESAC) The obtained phase velocities range from 1.5 km/s to 0.3 km/s over the 1-10 Hz frequency band.
The group velocity dispersion curves are then inverted to infer a shallow shear-wave velocity model down to a depth of about 250 m, for the area of Pozzuoli-Solfatara. The shear-wave velocities thus obtained are compatible with those derived both from cross- and down-hole measurements in neighbour wells and from laboratory experiments. These data are eventually interpreted in the light of the geological setting of the area.
I perform an attenuation study on array recordings of the signals generated by the shots. The attenuation curve was retrieved by analysing the amplitude spectral decay of Rayleigh waves with the distance, in different frequency bands. The attenuation curve was then inverted to infer the shallow Q inverse model.
Using the obtained velocity and attenuation model, I calculate the theoretical ground response to a vertically-incident SH wave obtaining two main amplification peaks centered at frequencies of 2.1 and 5.4 Hz. The transfer function was compared with those obtained experimentally from the application of Nakamura’s technique to microtremor data, artificial explosions and local earthquakes. Agreement among the transfer functions is observed only for the amplification peak of frequency 5.4 Hz.
Finally, as a complementary contribution that might be used for the assessment of seismic risk in the investigated area, I evaluate the peak ground acceleration (PGA) for the whole Campi Flegrei caldera and locally for the Pozzuoli-Solfatara area, by performing stochastic simulations of ground motion, partially constrained by the previously described results. Two different methods (random vibration theory (RVT) and ground motion generated from a Gaussian distribution (GMG)) are used, providing the PGA values of 0.04 g and 0.097 g for Campi Flegrei and Pozzuoli-Solfatara, respectively.Università degli Studi di Napoli Federico IIPublishedope
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Il soggetto (collettivo) contiene il male? Dupuy e Girard tra scienze sociali e teologia politica
No full textA partire dalla configurazione della teoria del male nella teoria mimetica di Girard e nella ripresa della questione nella visione di Dupuy del nesso tra economia, male e sacrificio l'articolo chiarisce come la categoria della soggettività consenta di individuare il problema del contenimento del male secondo l'adagio per cui la dinamica collettiva dell'azione studiata dalle scienze sociali e giuridiche contiene il male nel duplice senso che lo mostra dentro di sé e al tempo stesso lo limita, provando a trarre alcune implicazione di questo accostamento per la categoria della teologia politica
Recalibration of the magnitude scales at Campi Flegrei Italy, on the basis of measured path and site and transfer functions
No full textNew duration-based local (ML) and moment (Mw) magnitude scales are obtained the Campi Flegrei area through analysis of a dataset of local volcano-tectonic earthquakes. First, the S-wave quality factor for the investigated area was experimentally calculated, and then the distance-correction curve, logAO(r), to be used in the Richter formula ML = log Amax - log AO(r), was numerically estimated by measuring the attenuation properties and, hence, propagating a synthetic S-wave packet in the earth medium. The local magnitude scale was normalized to fit the Richter formula that was valid for Southern California at a distance of 10 km. ML was estimated by synthesizing Wood-Anderson seismograms and measuring the maximum amplitude. For the same dataset, the moment magnitude was obtained from S-wave distance-corrected and site-corrected displacement spectra. Comparisons between local and moment magnitudes determined, along with the old duration magnitude (MD) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Vesuviano, are presented and discussed. Moreover, the relationships between ML and Mw calculated for two reference sites are also derived
Fast wavefield decomposition of volcano-tectonic earthquakes into polarized P and S waves by Independent Component Analysis
No full textIn 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
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