• In this work, we study the crust and the uppermost mantle structure beneath the Sicily Channel, by applying the ambient noise and earthquake tomography method. After computing cross-correlation of the continuous ambient noise signals and processing the earthquake data, we extracted 104 group velocity and 68 phase velocity dispersion curves corresponding to the fundamental mode of the Rayleigh waves. We computed the average velocity of those dispersion curves to obtain tomographic maps at periods ranging from 5 s to 40 s for the group velocities and from 10 s to 70 for the phase velocities. We inverted group and phase speeds to get the shear-wave velocity structure from the surface down to 100 km depth with a lateral resolution of about 200 km. The resulted velocity models reveal a thin crust with thickness value of 15 km beneath the southern part of the Tyrrhenian basin and a thickness value of 20 km beneath Mount Etna. The obtained thickness values are well correlated with the reported extension of the Tyrrhenian lithosphere due to the past earthquake tomography subduction and rollback of the Ionian slab beneath the Calabrian Arc. The crustal thickness increases and reaches values between 28 and 30 km beneath the Tunisian coasts and Sicily Channel. The S-wave models reveal also the presence of high velocity body beneath the island of Sicily. This finding can be interpreted as the presence of the Ionian slab subducting beneath the Calabrian Arc. Another high velocity body is observed beneath the southern part of the Tyrrhenian basin, it might be interpreted as the presence of fragments of the African continental lithosphere beneath the Tyrrhenian basin.

The city of Aïn Témouchent, located in northwest Algeria at the westernmost part of the Lower Cheliff Basin, has experienced several moderate earthquakes, the most significant of which occurred on 22 December 1999 (Mw 5.7, 25 fatalities, severe damage). In this study, ambient noise measurements from 62 sites were analyzed using the horizontal-to-vertical spectral ratio (HVSR) method to estimate fundamental frequency ($f_0$) and amplitude ($A_0$). The inversion of HVSR curves provided sedimentary layer thickness and shear wave velocity (Vs) estimates. Additionally, four spatial autocorrelation (SPAC) array measurements refined the Rayleigh wave dispersion curves, improving Vs profiles (150–1350 m/s) and sediment thickness estimates (up to 390 m in the industrial zone). Vs30 and vulnerability index maps were developed to classify soil types and assess liquefaction potential within the city.

This study investigates the structure of shear-wave velocities (Vs) in the shallow layers of the Oran region, north-west of Algeria, using non-invasive techniques based on ambient vibration arrays. The region has experienced several moderate earthquakes, including the historical Oran earthquake of 1790. Ambient vibration measurements were carried out at 15 sites throughout the study area. Two methods were used: spatial autocorrelation (SPAC) and frequency–wavenumber analysis (f-k), which allowed us to better constrain Rayleigh wave dispersion curves. The inversion of the dispersion curves derived from the f-k analysis allowed for estimating the shear-wave velocity profiles and the V_s30 value at the sites under study. The other important result of the present study is an empirical equation that has been proposed to predict V_s30 in the Oran region. The determination of near-surface shear-wave velocity profiles is an important step in the assessment of seismic hazard. This study has demonstrated the effectiveness of using ambient vibration array techniques to estimate the soil Vs structure.

The city of Aïn Témouchent, located in northwest Algeria at the westernmost part of the Lower-Cheliff Basin, has experienced several moderate earthquakes in the past. The most significant event occurred on December 22, 1999, with a magnitude of Mw 5.7, resulting in 25 fatalities and severe damage to the town center. In this study, ambient noise measurements from 62 sites have been analyzed using the horizontal-to-vertical spectral ratio (HVSR) method to estimate the fundamental ground frequencies (f₀) and their corresponding amplitudes (A₀). The results reveal that f₀ varies between 0.8 and 4.8 Hz, with amplitudes ranging from 2 to 5.6. The inversion of the HVSR curves enabled the estimation of the sedimentary layer profiles, with the corresponding thickness variation and shear–wave velocity for each layer. Additionally, four array measurement points across the city center were carried out using the spatial autocorrelation (SPAC) method to derive Rayleigh wave dispersion curves. The inversion of these curves provided more precise layer parameters and improved the estimation of Vs profiles, particularly at shallow depths. The results indicate shallow layer velocities varying between 150 and 1350 m/s, with maximum sediment thickness reaching 390 m in the industrial zone, northeast of the city. Furthermore, Vs30 and vulnerability index maps have been developed to classify soil types and assess liquefaction potential within the city.