Petrosino, Simona
(2006)
Attenuation and velocity structure in the area of
PozzuoliSolfatara (Campi Flegrei, Italy) for the estimate of local site response.
[Tesi di dottorato]
(Inedito)
Tipologia del documento: 
Tesi di dottorato

Lingua: 
English 
Titolo: 
Attenuation and velocity structure in the area of
PozzuoliSolfatara (Campi Flegrei, Italy) for the estimate of local site response 
Autori: 
Autore  Email 

Petrosino, Simona  [non definito] 

Data: 
2006 
Tipo di data: 
Pubblicazione 
Numero di pagine: 
101 
Istituzione: 
Università degli Studi di Napoli Federico II 
Dipartimento: 
Scienze fisiche 
Dottorato: 
Rischio sismico 
Ciclo di dottorato: 
18 
Coordinatore del Corso di dottorato: 
nome  email 

Gasparini, Paolo  [non definito] 

Tutor: 
nome  email 

Del Pezzo, Edoardo  [non definito] 

Data: 
2006 
Numero di pagine: 
101 
Settori scientificodisciplinari del MIUR: 
Area 04  Scienze della terra > GEO/10  Geofisica della terra solida 
Depositato il: 
18 Giu 2008 
Ultima modifica: 
30 Apr 2014 19:30 
URI: 
http://www.fedoa.unina.it/id/eprint/2469 
DOI: 
10.6092/UNINA/FEDOA/2469 
Abstract
In the present work I infer the 1D shearwave velocity model in the volcanic area of PozzuoliSolfatara using the dispersion properties of both Rayleigh waves generated by artificial explosions and microtremor. The groupvelocity dispersion curves are retrieved from application of the Multiple Filter Technique (MFT) to singlestation recordings of airgun 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 Rayleighwave fundamentalmode group velocities ranging from about 0.8 to 0.6 km/sec over the 112 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 110 Hz frequency band.
The group velocity dispersion curves are then inverted to infer a shallow shearwave velocity model down to a depth of about 250 m, for the area of PozzuoliSolfatara. The shearwave velocities thus obtained are compatible with those derived both from cross and downhole 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 verticallyincident SHwave 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 PozzuoliSolfatara 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 PozzuoliSolfatara, respectively.
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