## 5 Data Acquisition and Processing  
### Data Acquisition  
Ambient vibrations were recorded using single-station and array measurement techniques. The HVSR method was applied at 164 ambient vibration measurement points, distributed over 20 profiles (Figure 3). The measurements were made following SESAME recommendations [54]. The F-K method was applied to array measurements in seven sites. Additional measurements, using the electrical prospection technique, were carried out in the Mecheta-Nouasser and El-Amra regions. The aim was to determine the thicknesses of the Plio-Quaternary layers for the HVSR inversion. It is well-known that, in a sedimentary basin, the maximum depth to bedrock is observed beneath the youngest formations, which are generally located in the middle of the basin. Thus, ambient vibrations were recorded mainly in the Quaternary plain of the Middle-Chelif, from Zbabdja village in the west to Ain-Defla in the east (Figure 3). Moreover, in order to better image the synclinal shape of the basin, the HVSR profiles are perpendicular to its axis, varying from a WNW-ESE direction in Oued-Fodda to a NNW-SSE in the rest of the plain. The single-station measurements were carried out in calm weather, with a recording time of 16 min away from human activities, and 26 min inside cities and villages. Ambient vibrations were recorded using Tromino seismographs, with a sampling rate of 512 samples per second. The first array measurement campaign (AR1, AR4, and AR2 in Figure 4) was carried out in February 2019, using between seven and nine Mark L22 seismographs (f\({}_{0}\) = 2 Hz) set in a circular configuration, with two apertures of 20 m and 50 m, respectively, at each site. The vertical components of these sensors were plugged into an Arduino-based multichannel acquisition system [55] for 30 min of simultaneous recording at each site. The second measurement campaign (AR3, AR5, AR6, and AR7) was carried out in September 2020, using nine new SS10 (f\({}_{0}\) = 1 Hz) triaxial velocity sensors connected to their respective \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Per/Epoch.** & **Age** & **Rock** & **Thickness (m)** & **Vp (m/s)** & **Vs (m/s)** & **\(\sigma\) (KN/m3)** & **References** \\ \hline \multirow{3}{*}{Quaternary} & Hl & Alluviums & 2–20 & 350–600 & 200–350 & 16–18 & [6,7,17,18,22] \\ \cline{2-8}  & Ps & Clays \& Conglomerates & 10–100 & 600–1700 & 400–700 & 18–22 & [6,7,17] \\ \hline \multirow{3}{*}{Pliocene} & As & Sands \& Conglomerates & 10–80 & 550–2000 & 350–750 & 17–22 & [7,17] \\ \cline{2-8}  & Pl & Sands \& Conglomerates & 30–80 & 750–2400 & 500–900 & 19–23 & [7,17] \\ \hline \multirow{3}{*}{Mioceene} & Ms & Marls & 30–80 & 1100–2900 & 700–1200 & 20–24 & [7,17] \\ \cline{2-8}  & Tr & Limestones \& Sandstones & 40–150 & 1300–3200 & 900–1300 & 23–25 & [7,17] \\ \cline{2-8}  & Sr-Tr & Clays \& Marls & 100–450 & 1200–3400 & 800–1400 & 21–25 & [7,17,35] \\ \cline{2-8}  & Sr & Poudingues & 10–60 & 1900–3600 & 1300–1500 & 22–25 & [35] \\ \hline \multirow{3}{*}{Cretaceous} & Sn & Marls, clays \& & & & & & \\  & Quartzites & - & 2600–4600 & 1800–2500 & 24–27 & [22] \\ \hline Jurassicque & - & Limestones & - & 3000–5000 & 2000–2800 & 25–27 & [53] \\ \hline \end{tabular}
\end{table} 
Table 1: Geotechnical information used for the inversion process. Hl: Holocene. Ps: Pleistocene. As: Asian. Pl: Placenzian. Ms: Messinian. Tr: Tortonian. Sr: Seravallian. Sn: Senonian. SL06 digitizers (SARA electronic instruments). The dispersion curves obtained in this way produced good resolution only for the first 50 m of the soil column. Thus, additional single-station measurement points were carried out at the center of each array, recording ambient vibrations at the same time in order to perform a joint inversion and, thus, obtain a better resolution in the shallow and deep sediments. For the electrical resistivity tomography survey, we used a set of 40 electrodes in dipole-dipole devices, linked to an ABEM Ter Terameter LS 2 resistivity meter.