1,721,392 research outputs found
Analysis of PS-to-PP amplitude ratios for seismic reflector characterisation: method and application
No full textElastic parameters derived from seismic reflection data provide
information on the lithological contrast at an interface and support the geological
interpretation.We present a method to estimate elastic parameter contrasts
at a given interface in a 1-D layered medium from PS-to-PP amplitude ratios.
The method is applied to synthetic data to demonstrate its possibilities and limitations.
First results for real data acquired in the Campi Flegrei caldera (southern
Italy) reveal a gas-bearing layer at around 3 km depth and indicate a strong
negative velocity contrast at 7.5 km depth, possibly related to the presence of
partial melt.I.N.G.V.Published1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveope
Use of small earthquake records to determine the source time functions of larger earthquakes: an alternative method and an application
No full textSmall earthquake records are increasingly being used as empirical Green's functions to estimate the source time functions (STFs) of large earthquakes. This is generally accomplished in the frequency domain by computing the ratio of the large to the small event spectrum and then transforming it back to the time domain. This study proposes an alternative method in which a large-event STF is approximated by a series of pseudotriangular pulses whose parameters are determined by a nonlinear frequency-domain inversion, involving the spectrum of the large and the small events. The method allows a "positivity' constraint to be imposed on the STF. The misfit between the observed and computed large-event seismograms is measured in the frequency domain over the range of frequency in which the data are reliable. -from Author
Un metodo di inversione congiunta dei parametri di sorgente e della struttura di attenuazione del mezzo di propagazione: applicazione ai dati di microterremoti dei Campi Flegrei (1984)
No full textSource parameters and three-dimensional attenuation structure from the inversion of microearthquake pulse width data: Method and synthetic tests
No full textSource, attenuation and site parameters of the 1997 Umbria-Marche seismic sequence from the inversion of P wave spectra: a comparison between constant Q and frequency dependent Q models
No full textLe Azioni di Piano nella realtà socio-economica locale.
No full textIl volume riporta i risultati delle ricerche svolte per la redazione del Piano di Gestione del Sito di Interesse Comunitario
IT 7120215 “Torre del Cerrano”, svolte con un finanziamento Regione Abruzzo reperito dal Consorzio di Gestione dell’Area
Marina Protetta Torre del Cerrano
Geophysical Exploration of the Campi Flegrei (Southern Italy) Caldera’ Interiors: Data, Methods and Results
No full textSource, attenuation, and site parameters of the 1997 Umbria-Marche seismic sequence from the inversion of P wave spectra: A comparison between constant Q(P) and frequency-dependent Q(P) models RID C-3422-2011 RID B-5344-2010
No full textThe attenuation of P waves, the site responses, and the source parameters (seismic moment, corner frequency, source dimension) of 490 seismic events that occurred during the 1997 Colfiorito, Umbria-Marche seismic sequence have been inferred from the inversion of P wave velocity spectra. The Boatwright source model has been assumed to model the source spectra. A global nonlinear inversion scheme was developed to avoid any a priori selection of the initial Q(P) and the corner frequency. To establish if a frequency-dependent Q(P) model fits the data better than a constant Q(P) model, two inversion results have been compared. Application of the Akaike information criterion indicates that the constant Q(P) model represents the best compromise between model simplicity and data misfit. The station Q(P) values are small: in the range of 50 to 200. A one-dimensional Q(P) model is obtained by back projecting the inverted t*. Our results indicate both well-defined near-site attenuation effects at some sites and heterogeneity in the inelastic properties of the crust. With the exception of the amplification response at five seismic stations, most of the recording sites did not show amplification peaks at particular frequencies. The stress drop clearly increases as a function of the seismic moment, which indicates a deviation from self-similarity, whereas it does not show an increase with depth, probably owing to the effects of fluid pressurization in the crust. A stress drop of about 39 MPa is inferred. The relationship between the seismic moment and the local magnitude for P waves has been calibrated
Earthquake Seismic Moment, Rupture Radius, and Stress Drop from P-Wave Displacement Amplitude Versus Time Curves
No full textThe reliable determination of earthquake source parameters is a relevant task of seismological investigations which ground nowadays on high-quality seismic waveforms collected by near-source dense arrays of ground motion sensors. Here, we propose a parametric modeling technique which analyzes the time-domain P-wave signal recorded in the near-source range of small-to-large-size earthquakes. Assuming a triangular moment rate function, a uniform speed, and circular rupture model, we develop the equations to estimate the seismic moment, rupture radius, and stress drop from the corner time and plateau level of the average logarithm of the P-wave displacement versus time curves (LPDT). The constant- Q , anelastic attenuation effect, is accounted by a postprocessing procedure that evaluates the Q -unperturbed moment rate triangular shape. The methodology has been validated through application to the acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan earthquake sequences covering a wide moment magnitude range (Mw 2.5-6.5) and recording distance <100 km. After correcting for the anelastic attenuation function, the estimated average stress drop and the confidence interval ( langle Delta sigma
angle =0.60 (0.42-0.87) MPa and langle Delta sigma
angle =1.53 (1.01-2.31) for crustal and subcrustal events of Japan and langle Delta sigma
angle =0.36 (0.30-0.44) MPa for Central Italy) show for both regions a self-similar, constant stress drop scaling of the rupture duration/radius with seismic moment. The smaller sensitivity of the spatially averaged, time-varying peak displacement amplitude to the radiation from localized high slip patch on the fracture surface could explain the retrieved smaller average stress drops for subcrustal earthquakes in Japan and M >5.5 events in Central Italy relative to previous estimates using spectral methods
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