Geotechnical Site Characterisation in the Umbria-Marche Area and Evaluation of Earthquake Site-Response

Abstract

In this research a site classification is proposed for the Umbria-Marche area (central Italy), based on geotechnical and geomorphological criteria. Two empirical techniques to evaluate site effects are used, namely the generalised spectral inversion, and the horizontal to vertical spectral ratio. The soil transfer functions obtained by the two techniques are compared in order to capture the features common to each class and verify the accuracy of the classification.We used strong ground motions recorded during the Umbria-Marche seismic sequence (September 1997-May 1998) and we selected 25 sites that were classified into four groups. The results of the empirical techniques have also been tested using theoretical 1-D or 2-D methods that are commonly used to simulate linear soil behaviour. The results, expressed in terms of amplitude transfer functions, are shown according to each soil class and confirm the consistency of the site characterisation. The empirical techniques are efficient in detecting the fundamental frequency of vibration but seldom the higher harmonics. Conversely, the peak amplitude of the transfer functions is not consistently determined, especially for sites located in deep sedimentary basins, where 2-D effects occur and simplified methods, such as the horizontal to vertical spectral ratios (HVSR) or 1-D theoretical models frequently fail. Significant amplifications are also found for 2-D rock structures such as rock crests or cliffs.

Ground motion prediction equations derived from the Italian strong motion database

“…The design matrix used to compute the covariance matrix is the Jacobian matrix derived from equation (1) installed at the Nocera Umbra (Central Italy) station. The site response of Nocera Umbra station has been deeply investigated by previous studies demonstrating that large amplifications occur around 6 Hz (e.g., Rovelli et al, 2002;Castro et al, 2004;Luzi et al, 2005). For this reasons the amplitude of coefficient s 5 as a function of period, shown in In order to assess the effect of including classes D and E on the median model, the regression was also performed removing the records relative to these two classes.…”

Urban Geology, Earthquake and Planning by Means of GIS for Development Needs, A Case Study, Iran

“…There are several ways of assessing site effects. The characterization of a given site can be achieved based on Instrumental or theoretical-analytical or numericalapproaches to the problem [8,9,10]. In order to classify the regions of the city in terms of site stability for building reconstructions for future urban planning, I performed several investigation case studies on soil and subsurface sediments in 5 cities of Iran and here I want to introduce some results of them in this paper.…”

GIS-based regional assessment of seismic site effects considering the spatial uncertainty of site-specific geotechnical characteristics in coastal and inland urban areas

“…Metropolitan areas in Korea have a low absolute seismic risk and have experienced few modern earthquake disasters. Nevertheless, the absolute earthquake risk potential is higher than in the country's mountainous areas because there are greater soft soil deposits in coastal and riverside locations in metropolitan areas (Luzi et al 2005). Moreover, most urban areas are densely situated on plains surrounded by mountains; regional geology plays a role in site effects and earthquake-induced hazards in cities.…”