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In this paper we evaluate the local seismic response for thirteen sites located in the municipalities of Arquata del Tronto and Montegallo, two areas which suffered heavy damage during the Mw 6.0 and Mw 5.4 earthquakes which struck Central Italy on August 24, 2016. The input dataset is made by ground motion recordings of 348 events occurred during the sequence. The spectral site response is estimated by the Generalized Inversion Technique and makes use of reference sites. The interpretation is further improved through the information provided by a reference-site independent method (i.e., the so called Receiver-Function Technique) and by the Horizontal-to-Vertical Spectral Ratios of ambient noise recordings. We also provide an independent estimate of the local amplification by comparing the Peak Ground Velocity and the Spectral Amplitudes observed at each site to the value estimated by well-established Ground Motion Prediction Equations for a rock-class site. The results obtained by the adopted methodologies are all highly consistent, and they emphasize the different seismic behavior of several sites at local scale. Thus, sites located on Quaternary deposits overlying the bedrock, such as Castro, Pretare, Spelonga, Pescara del Tronto, and Capodacqua feature some relevant amplifications in a medium (2-10 Hz) frequency range; two sites at Spelonga show amplifications also at low frequencies; three sites located on stiff formations, i.e. Uscerno, Balzo and Colle d'Arquata, respectively, feature either nearly neutral response or low amplification level. A probable topographic effect was identified at the rock site of Rocca di Arquata (MZ80).

We use previously determined direct-wave attenuation functions as well as stable, codaderived source excitation spectra to isolate the absolute S-wave site e ect for the horizontal and vertical components of weak ground motion. We used selected stations in the seismic network of the eastern Alps, and nd the following: (1) all "hard rock"sites exhibited deampli cation phenomena due to absorption at frequencies ranging between 0.5 and 12 Hz (the available bandwidth), on both the horizontal and vertical components (2) "hard rock" site transfer functions showed large variability at high-frequency (3) vertical-motion site transfer functions show strong frequency-dependence, and (4) H/V spectral ratios do not reproduce the charactersitics of the true horizontal site transfer functions (5) traditional, relative site terms obtained by using reference "rock sites" can be misleading in inferring the behaviors of true site transfer functions, since most rock sites have non-at responses due to shallow heterogeneities resulting from varying degrees of weathering.We also use our stable source spectra to estimate total radiated seismic energy and compare against previous results. We nd that the earthquakes in this region exhibit nonconstant dynamic stress drop scaling which g i v es further support for a fundamental di erence in rupture dynamics between small and large earthquakes.To correct the vertical and horizontal S-wave spectra for attenuation, we used detailed regional attenuation functions derived by Malagnini et al. (2002) who determined frequencydependent geometrical spreading and Q for the region. These corrections account for the gross path e ects (i.e., all distance-dependent e ects), although the source and site e ects are still present in the distance-corrected spectra. The main goal of this study is to isolate the absolute site e ect (as a function of frequency) by removing the source spectrum (momentrate spectrum) from the distance-corrected S-wave spectra. Typically, r e m o ving the S-wave source spectrum is di cult because of inadequate corrections for the source radiation pattern, directivity and random interference. In addition to complexities near the source, 2-D and 3-D structure beneath the recording site will result in an azimuth-dependent site e ect. Since the direct wave only samples a narrow range in take-o and back-azimuth angles, multi-station 2 averaging is needed to minimize the inherent scatter.To minimize these complicating e ects, we apply the coda methodology outlined by Mayeda et al., (2003) to obtain stable moment-rate spectra. This methodology provides source amplitude and derived source spectra that are a factor of 3-to-4 times more stable than those derived from direct waves. Since the coda is commonly thought of as scattered energy that samples all ray parameters and back-azimuths, it is not very sensitive to the source radiation pattern and 3-D structure. This property makes it an excellent choice for use in obtaining average properties of the source, site and path e ects in ...

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The analysis of the time distribution of the major earthquakes that occurred in Italy since 1600 reveals that seismicity alternates periods of higher and lower activities over cycles of about 60 years. The same rhythm is present in the eruptive history of the Vesuvius. The large spatial scale of synchronization leads to suppose an external forcing. A hint on its possible origin comes from climatology, where a quasi 60 year cycle is found for various parameters and processes. A hypothesis, also supported by other studies, is that seismicity and volcanism are controlled by cycles of sea level rise. The mechanism could justify similar regularities observed for seismicity in other areas (e.g., cycles of earthquakes in the southern San Andreas Fault, in California) or for strong earthquakes at the global level. The increasing oceanic load of the last century could be coresponsible of the current long-lasting rest of the Vesuvius.