HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by MALAGNINI, L. Articles by SEEBER, L. Search for Related Content GeoRef GeoRef Citation

Site amplification estimates in the Garigliano valley, central Italy, based on dense array measurements of ambient noise

ISTITUTO NAZIONALE DI GEOFISICA, VIA DI VIGNA MURATA 605, 00143 ROMA, Italy
LAMONT-DOHERTY EARTH OBSERVATORY COLUMBIA UNIVERSITY, PALISADES, NEW YORK 10964

Abstract

A frequency-domain formulation of the Aki (1957, 1965) autocorrelation method has been applied to seismic noise recorded by a 100-m wide circular array deployed on soft Holocene sediments in the Garigliano river valley, where a large amplification of ground motion during earthquakes was experienced (Rovelli et al., 1988). The application of this method to ambient noise recordings demonstrates that microtremors in the valley are dispersive and dominated by surface waves. By assuming that the vertical component reflects Rayleigh wave motion, we obtain a dispersion curve that is interpreted in terms of a layered shear-wave velocity structure. Layer thicknesses are constrained by the stratigraphic information provided by a deep hole drilled in the area, and shear velocities are estimated by means of a trial-and-error approach to achieve a satisfactory fit of the ambient noise dispersion. The best-fit velocity model is used to compute a theoretical transfer function, which is then compared with an average spectral ratio obtained from earthquake weak ground motions recorded at two stations, one in the valley and the other on a limestone reference site. An overall agreement is found between the theoretical curve and the observed spectral ratios. The discrepancies that do exist may be ascribed to the assumption of 1-D inhomogeneity which considerably simplifies the theoretical transfer function.

Our results show that the spatial-correlation method can be useful to infer velocity structure down to depths of hundreds of meters, when generalized geological informations are available, and can thus provide useful constraints for theoretical methodologies for the prediction of site response.

Footnotes

^* Present address of S. E. Hough. United States Geological Survey, 5250 South Wilson Avenue, Pasadena, California 91106.

This article has been cited by other articles:

				Estimation of S-Wave Velocity Structures in and around the Sendai Basin, Japan, Using Array Records of Microtremors Bulletin of the Seismological Society of America, April 1, 2001; 91(2): 206 - 218.

				B. Chouet, G. De Luca, G. Milana, P. Dawson, M. Martini, and R. Scarpa Shallow velocity structure of Stromboli volcano, Italy, derived from small-aperture array measurements of Strombolian tremor Bulletin of the Seismological Society of America, June 1, 1998; 88(3): 653 - 666. [Abstract] [PDF]

				H. van de Vrugt, S. Day, H. Magistrale, and J. Weddberg Inversion of local earthquake data for site response in San Diego, California Bulletin of the Seismological Society of America, October 1, 1996; 86(5): 1447 - 1458. [Abstract] [PDF]

				H. J. Al-Shukri, G. L. Pavlis, and F. L. Vernon III Site effect observations from broadband arrays Bulletin of the Seismological Society of America, December 1, 1995; 85(6): 1758 - 1769. [Abstract] [PDF]