## 5 Conclusions  
The study provides fundamental frequencies and Vs profiles for the city of Ain Temouchent, offering essential data for seismic hazard assessment and risk mitigation. The identification of fundamental frequency (\(f_{0}\)) and vulnerability index (\(Kg\)) enables the detection of areas where seismic amplification effects are likely to occur, which is critical for  
Figure 12: The depth to bedrock is expressed as a function of the fundamental frequency, shown by the black line. In this relationship, \(a\) and \(b\) are the regression coefficients, \(f_{0}\) is the fundamental frequency, \(D\) is the depth to bedrock, and R is the correlation coefficient. earthquake-resistant building design. The city holds particular importance as a seismic hazard study zone, having been severely impacted by the 1999 earthquake. While this study provides valuable insights into the subsurface structure and site effects in Ain Temouchent, certain limitations must be acknowledged. First, the HVSR method, although widely used, does not provide absolute site amplification factors, requiring additional validation through numerical modeling or direct ground motion recordings. Moreover, the resolution of shear wave velocity profiles is constrained by the depth penetration of ambient noise waves, which could be improved by combining passive seismic techniques with active-source methods. The research aims to improve the understanding of site effects and provide a more detailed characterization of the subsoil. The key findings and conclusions are summarized as follows:  
* Environmental noise analysis: Using the HVSR method to analyze ambient environmental noise, the study identifies predominant single-peak curves across the study area, with the fundamental frequency (\(f_{0}\)) ranging between 0.8 and 4.8 Hz. In areas with Quaternary deposits, two frequency peaks are observed. The secondary frequency peak (6-15 Hz) corresponds to impedance contrasts at shallow depths between Quaternary and Mio-Pliocene deposits. * Stratigraphic model: The HVSR and dispersion curve inversion reveals a five-layer stratigraphic structure for the city. The Quaternary layer, at the surface, exhibits shear wave velocities of 150-350 m/s and thicknesses ranging from 1 to 14 m. Beneath this is the Pliocene layer, with shear wave velocities of 350-500 m/s and thicknesses of 1 to 43 m. Below the Pliocene, the Miocene layer is identified, characterized by shear wave velocities of 500-850 m/s and thicknesses of 10 to 124 m. Deeper still, the Lower Miocene sediments show velocities of 850-1350 m/s and thicknesses of 47 to 284 m. At the base of the sequence lies the Mesozoic basement, composed of Cretaceous and/or Jurassic materials, with shear wave velocities ranging from 1400 to 2600 m/s. * Lateral variations: The inversion of HVSR curves highlights significant lateral variations in both shear wave velocity and sediment thickness across Ain Temouchent. The resulting shear wave velocity models offer valuable insights for simulating ground motions in the far western region of the Lower Cheliff Basin. * Soil and liquefaction potential: The area is predominantly composed of very dense soils and soft rocks, with stiff soils concentrated in and south of the industrial zone. The vulnerability index (\(Kg\)) shows a marked increase in the industrial zone, indicating a higher potential for liquefaction. These findings can be directly integrated into local seismic microzonation studies and to help urban planners and engineers adopt suitable construction techniques in high-risk areas. Additionally, the shear wave velocity models and sediment thickness estimations can improve numerical simulations of ground motion and refine liquefaction susceptibility maps. Finally, the obtained results could be used to update the Algerian seismic code and inform urban planning and construction practices in the region. Methodology, F.S. and J.J.G.-M.; validation, A.I. and B.M. ; formal analysis, A.S.; investigation, A.S.; data curation, A.S., A.I. and B.M.