In this study we investigate the site amplification effects observed in the Gubbio plain, central Italy. The recordings of 140 local earthquakes (1:2 ≤ Ml ≤ 4:7) observed by two linear arrays installed along the longitudinal and perpendicular basin axis are analyzed both in the time and frequency domains to determine the spatial variation of the local site effects in the basin. The time series recorded in the Gubbio plain are characterized by locally generated surface waves, which cause a significant increase in both ground-motion duration and amplitude with respect to a nearby reference station on a rock site. In the middle of the basin where the sedimentary cover is thickest (ca 600 m), the peak ground velocity is amplified on average by a factor of 5 with respect to the reference station installed on rock, and the duration is increased by a factor of about 2. The analyses in the frequency domain show that the spectral energy of the basin-generated waves is mainly distributed over the range 0.4–2 Hz and affects both horizontal and vertical components. The site responses estimated by applying two reference site methods show that the overall shape of the amplification functions is similar for the sites located inside the basin with a difference in the amplification levels, which can reach values as high as 30 in the middle of the valley. Amplifications up to a factor of 10 affect the vertical component of ground motion over a broad frequency range for nearly all basin sites with the maximum amplifications occurring at around 1 Hz. Finally, although the horizontal-to-vertical spectral ratios were found to provide a reliable estimation of the fundamental resonance frequency of the site, they fail to estimate the shape of the site transfer functio

From March to September 2009, a velocimetric network was installed in Narni, central Italy, a village on the top of a limestone ridge. The aim was to investigate local site effects due to the 220-m-high ridge, which is characterized by slopes ranging from 22° to 35°. To investigate amplification without and with a reference site, three stations were installed at the base of the hill and seven at the crest. The network recorded 702 earthquakes, many of them from the 2009 L'Aquila sequence. To determine the dependence of amplification on the morphological features, the spectra were computed for horizontal components rotated into a range of azimuths. Both the ratio of the horizontal-to-vertical-component spectra and the ratio of the spectra at the ridge crest with respect to a reference station at the base of the ridge showed amplification by a factor of ca. 4.5 for frequencies between 4 Hz and 5 Hz. The highest amplifications were seen for the directions of the ground motion perpendicular to the main elongation of the ridge. Finally, considering events with an epicentral distance less than 30 km, empirical ground motion models were calibrated for maximum horizontal peak ground acceleration, velocity and acceleration response spectra (5% damping) up to 1 s, to estimate the site corrective coefficients for topographic amplification. The data show corrective coefficients between 0.35 and 0.48 (log10 scale; amplification, 2.2-3.0) for the spectral ordinates between 0.2 s and 0.3 s

The scope of this work is to examine the influence of the uncertainty in soil modeling on numerical ground response estimates through a comprehensive sensitivity analysis. This allows identification of those parameters with the largest effect on both soil amplification (quantified here by a frequency‐independent factor, F _a ) and fundamental frequency, f ₀ . Although extensively examined in previous articles, the effect of the input motion is also analyzed. The uncertainty affecting the shear wave velocity ( V _S ) profile was found to be the factor contributing most to the uncertainty of both F _a and f ₀ . The soil thickness was also found to play a key role, particularly in those cases where bedrock depth is unknown or largely uncertain. Although of secondary importance compared to the effect of V _S on F _a and f ₀ , the influence of the input motion cannot be neglected; rather it becomes predominant with regard to the uncertainty affecting frequency‐dependent shaking parameters.

In this study, microseism recordings from a near coast seismic station and concurrent significant sea wave heights ($$H_{\frac{1}{3}}$$) are analysed to calibrate an empirical relation for predicting sea wave height in the Ligurian Sea. The study stems from the investigation of the damaging sea storms occurred in the Ligurian Sea between 2008 October and November. Analysing data collected in this time frame allows identification of two types of microseism signal, one associated to the local sea wave motion and one attributable to a remote source area. The former is dominated by frequencies greater than 0.2 Hz and the latter by frequencies between 0.07 and 0.14 Hz. Moreover, comparison of microseism spectrogram and significant sea wave heights reveals a strong correlation in that the spectral energy content of microseism results proportional to the sea wave height observed in the same time window. Hence, an extended data set including also observations from January to December 2011 is used to calibrate an empirical predictive relation for sea wave height whose functional form is a modified version of the classical definition of $$H_{\frac{1}{3}}$$. By means of a Markov chain Monte Carlo algorithm we set up a procedure to investigate the inverse problem and to find a set of parameter values for predicting sea wave heights from microseism.