Characterization of the Sedimentary Cover in the City of Aïn Témouchent, North–Western Algeria, Using Ambient Noise Measurements

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.