ALBERT

Description: Ambient vibrations were recorded by two dense short-period seismic arrays located on Mount Vesuvius. The aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects. Mount Vesuvius, which is located in proximity to the Apennines earthquake source-zone, is one of the most dangerous volcanoes of the world. We compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field. The frequency-wavenumber (f-k) spectral method applied to the data recorded by array A furnished the Rayleigh waves and Love waves dispersive functions and proved the time-space stationarity of the noise wave field. The existence of a stochastic wave field justifies the use of the spatial autocorrelation (SPAC) method and the time stationarity autocorrelation (TSAC) method, which appear to be most effective at the lowest frequencies. The TSAC method, which time averages, is confirmed as the most user-friendly, because it does not require circular geometries. The knowledge of the surface structure is an important goal in site-effects studies and is used to determine the frequency response of the near-surface geology. Velocity models have been derived from the dispersion curves, using both trial and standard inversion procedure. The results are compared with those obtained from array measurements in adjacent areas (Scarpa et al., 2003), revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth. The shear-wave velocity profiles derived at the array-sites are used to model the 1D transfer functions for vertically incident shear waves. The fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal-to-vertical spectral ratios. The frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on Mount Vesuvius (Galluzzo et al., 2009).

Description: Cultural heritage represents our legacy with the past and our identity. However, to assure heritage can be passed on to future generations, it is required to put into the field knowledge as well as preventive and safeguard actions, especially for heritage located in seismic hazard-prone areas. With this in mind, the article deals with the analysis of ground response in the Avellino town (Campania, Southern Italy) and its correlation with the effects caused by the 23rd November 1980 Irpinia earthquake on the historical buildings. The aim is to get some clues about the earthquake damage cause-effect relationship. To estimate the ground motion response for Avellino, where strong-motion recordings are not available, we made use of the seismic hazard disaggregation. Then, we made extensive use of borehole data to build the lithological model so being able to assess the seismic ground response. Overall, results indicate that the complex subsoil layers influence the ground motion, particularly in the lowest period (0.1–0.5 s). The comparison with the observed damage of the selected historical buildings and the maximum acceleration expected indicates that the damage distribution cannot be explained by the surface geology effects alone.

Description: Mefite d’Ansanto (Italy) is a nonvolcanic field characterized by persistent strong degassing activity. A seismic field monitoring carried out during the Summer 2021 reveals a persis- tent, extended, and complex source of seismic tremor characterized by a spectrum with a frequency content from about 1 Hz to more than 35 Hz. While at frequency smaller than 3 Hz the signal amplitude is stationary, in the intermediate frequency band (3–20 Hz) sud- den changes of amplitude are often observed, suggesting the existence of an intermittent source (every few minutes to tens of minutes). Furthermore, very short bursts of high-fre- quency energy are recognized in the tremor signal. Results of array analysis and seismo- logical observation indicate that the sources of the analyzed tremor are located in a small area centered on the main vent of the degassing area. The persistent low-frequency tremor and the intermediate frequency signals propagate as surface waves to the seismic stations installed around the source and indicate a very shallow source. On the contrary, impulsive signals at frequencies greater than 20 Hz propagate as body waves, revealing a deeper source likely located between 50 and 100 m depth.

Description: Published

Description: 1102–1114

Description: JCR Journal