Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/12400
Authors: Pischiutta, Marta* 
Cianfarra, Paola* 
Salvini, Francesco* 
Cara, Fabrizio* 
Vannoli, Paola* 
Title: A systematic analysis of directional site effects at stations of the Italian seismic network to test the role of local topography
Issue Date: 2018
Series/Report no.: /214 (2018)
DOI: 10.1093/gji/ggy133
URI: http://hdl.handle.net/2122/12400
Keywords: Time-series analysis; Site effects; Wave scattering and diffraction; Wave propa- gation; Tectonics and landscape evolution
Abstract: Directional site effects observed at seismological stations on pronounced relief are analysed. We investigate the ground motion properties calculating horizontal-to-vertical spectral ratios and horizontal polarization of both ambient vibrations and earthquake records using broad- band seismograms of the Italian seismic network. We find that a subset of 47 stations with pronounced relief results in a significant (>2) directional amplification of the horizontal component, with a well-defined, site-specific direction of motion. However, the horizontal spectral response of sites is not uniform, varying from an isolated (resonant) frequency peak to a broad-band amplification, interesting frequency bands as large as 1–10 Hz in many cases. Using 47 selected stations, we have tried to establish a relation between directional amplification and topography geometry in a 2-D vision, when applicable, through a morphological analysis of the digital elevation model using geographic information systems. The procedure computes the parameters that characterize the geometry of topographic irregularities (size and slope), in combination with a principal component analysis that automatically yields the orientation of the elongated ridges. In seeking a relation between directional amplification and the surface morphology, we have found that it is impossible to fit the variety of observations with a resonant topography model as well as to identify common features in the ground motion behaviour for stations with similar topography typologies. We conclude that, rather than the shape of the topography, local structural complexities and details of the near-surface structure must play a predominant role in controlling ground motion properties at sites with pronounced relief.
Description: This article has been accepted for publication in Geophysical Journal International ©: The Authors 2018. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.
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