## 5 Conclusions  
In the present study, ambient vibration records were used to characterize the dynamic properties of the soil, and the velocity structure of its upper 30 m (\(V_{\rm s30}\)) in the cities of El-Attaf, Ain-Defla, and El-Abadia, in the Middle-Chelif Basin. Both single-station and array-based techniques were applied. The studied cities are a good example of growing cities located in a highly seismic zone. This study improves the one carried out by the WCC (1984) by investigating the behavior of the soils and quantifying the liquefaction potential. Additionally, the V\({}_{\rm s30}\) values allowed classifying the soils of the three cities for the first time. Figure 10: (**A**) Regression line (V\({}_{\rm S30}\) vs. V\({}_{\rm R41}\)) and equation given. R\({}^{2}\) is the correlation coefficient. (**B**) The corresponding residual values. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Site** & **Location.** & **V\({}_{\rm s30}\) (m/s)** & **Predicted V\({}_{\rm s30}\) (m/s)** & **Error (\%)** & **Actual Site** & **Predicted Site** \\  & & & & **Classification** & **Classification** \\ \hline \multicolumn{5}{c}{This study} \\ ATF1 & EL-Attaf & 349.85 & 371.64 & 5.9 & D & C \\ ATF2 & EL-Attaf & 373.97 & 399.10 & 6.3 & C & C \\ ATF3 & EL-Attaf & 379.08 & 379.27 & 0.0 & C & C \\ ATF4 & EL-Attaf & 367.03 & 366.05 & 0.3 & C & C \\ AIN1 & Ain-Defla & 505.73 & 477.42 & 6.0 & C & C \\ AIN2 & Ain-Defla & 535.85 & 541.50 & 1.0 & C & C \\ AIN3 & Ain-Defla & 270.42 & 251.42 & 7.6 & D & D \\ ABD1 & El-Abadia & 445.84 & 423.00 & 5.4 & C & C \\ ABD2 & El-Abadia & 352.64 & 351.30 & 0.4 & D & D \\ ABD3 & El-Abadia & 377.57 & 392.49 & 3.8 & C & C \\ ABD4 & El-Abadia & 345.05 & 349.98 & 1.4 & D & D \\  & & & Ref. [21] & & \\ AR1 & Oued-Fodda & 225.87 & 230.85 & 2.2 & D & D \\ AR2 & Oued-Fodda & 223.65 & 211.80 & 5.6 & D & D \\ AR3 & Oued-Fodda & 449.07 & 457.90 & 1.9 & C & C \\ AR4 & Oued-Fodda & 402.88 & 412.22 & 2.3 & C & C \\ AR5 & Oued-Fodda & 467.75 & 457.90 & 2.2 & C & C \\ AR7 & El-Amra & 454.45 & 469.59 & 3.2 & C & C \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Evaluation of V\({}_{\rm s30}\) predictive equation based on V\({}_{\rm s30}\) values obtained in this study, and in [21]. The HVSR technique was applied on single-station measurements to estimate the ground resonance frequencies. In the El-Attaf city, the frequencies vary between 1.2 and 8.3 Hz, and between 1.4 and 4.2 Hz in the El-Abadia city. In theAin-Defla city, the resonance frequencies vary between 1.4 and 4.5 Hz. The frequency peaks are directly related to impedance contrasts at different depths between sediments and bedrock. The corresponding amplitudes are ranging between 2 and 8.7. The obtained resonance frequencies and the corresponding amplitudes were used to calculate the shear strain, which may give an idea about possible behavior of the soils during major earthquakes. In the El-Abadia and Ain-Defla cities, the shear strain values reflect the elasto-plastic behavior of the soil column. Cracks and settlements may occur during earthquakes, especially in El-Abadia city. In El-Attaf, the shear strain analysis also shows an elasto-plastic behavior of the soil in most of the city. Except in its western part, where a collapse behavior is observed. Consequently, the soil is subject to liquefaction. Rayleigh wave dispersion curves were obtained from array recordings at 11 sites, using F-K, SPAC, and ESAC techniques. Shear-wave velocity models were obtained from the inversion of the mean dispersion curves. From the V\({}_{\text{s30}}\) variation maps, the local soils were classified using the NEHRP chart for site classification. In the El-Attaf city, the V\({}_{\text{s30}}\) values vary between 300 and 470 m/s. The soil is classified as very dense and soft rock (C) in most of the city. In the Ain-Defla city, V\({}_{\text{s30}}\) values vary between 250 and 530 m/s. The soils are classified as very dense (C) in the central and eastern sides. In the west, the soils are stiff (D) due to the thickening of the Quaternary alluviums.