## 2 Geological Framework  
The Cheliff Basin is the largest Neogene basin in northern Algeria [7]. In its major part, the sedimentary cover is made up of marine, continental, and sometimes lacustrine sedimentary rocks of the Neogene and Quaternary ages. However, in the plain of Ain Temouchent, which is located in the westernmost part of the Lower Cheliff Basin, the context is somewhat different, with the subsoil being characterized by the strong presence of eruptive rocks of the Quaternary and Miocene ages [13]. In fact, the western part of the Lower Cheliff Basin has been the site of two distinct volcano episodes: the first, of Calco-Alkaline type, took place in the Messinian (Upper Miocene); while the second, of alkaline basaltic type, occurred in the Quaternary [13; 14]. These deposits were only slightly affected by the NS to NW-SE compressive phase of the Quaternary, which may explain why seismic activity is relatively low compared to other areas of the Tellian Atlas [10; 13].  
The plain of Ain Temouchen is bordered from the east and south by the Tessala Mountains, from the north by the Mleta Plain, and from the west by the Tlemcen Mountains (Figure 1). The city of Ain Temouchen is located in the central part of the plain. From a lithological point of view, although the city is located in the central part of the plain, the soil structure is highly diversified (Figure 2). In most of the city, the soil is made up of Messinian formations (Upper Miocene), composed of several layers of silty clay, marl, limestone, and gravel [13]. These layers are thick, and according to the boreholes provided by LNHC and LTPO laboratories (Table 1), their thickness can exceed 100 m. The Messinian clays and marls are less developed in the plain of Ain Temouchent than in the Oranie plain, where their thickness reaches 400 m [45]. Quaternary and Miocene eruptive formations outcrop to the NW and S of the city, reaching maximum thicknesses of 46 m and resting on Messinian clays. Some recent alluvial and calcareous deposits are found at the city's extremities. In the western part of the city, the Quaternary formations rest directly on the Miocene sediments. To the east, a thin layer of Pliocene sand and sandy silt separates them. According to the available boreholes, the thickness of the sandy layers does not exceed 17 m.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Borehole** & **Quaternary [m]** & **Piocene [m]** & \multicolumn{2}{c}{**Miocene [m]**} \\ \hline F1 & 14.0 & \textgreater{}13 & 0.0 & – & \\ \hline F2 & 14.0 & 7 & 0.0 & 78 & 0.0 \\ \hline F3 & 14.0 & 7 & 0.0 & 78 & 0.0 \\ \hline F5 & 7.5 & \textgreater{}10 & 0.0 & – & \\ \hline F6 & 1.0 & – & & \textgreater{}35 & 0.0 \\ \hline F7 & 1.0 & – & & \textgreater{}19 & 0.0 \\ \hline F8 & 2.0 & \textgreater{}9 & 0.5 & – & \\ \hline F9 & 2.0 & 17 & 0.0 & \textgreater{}2 & 0.0 \\ \hline F10 & 4.0 & \textgreater{}5 & 0.5 & – & \\ \hline F11 & 4.0 & \textgreater{}5 & 0.5 & – & \\ \hline F14 & 1.0 & 4 & 0.0 & \textgreater{}11.0 & \\ \hline F17 & 8.0 & \textgreater{}10 & 0.0 & – & \\ \hline F21 & 2.0 & – & & \textgreater{}20 & 0.0 \\ \hline F26 & 1.0 & – & & \textgreater{}7 & 0.0 \\ \hline F30 & 7.5 & \textgreater{}10 & 0.0 & – & \\ \hline F34 & \textgreater{}12.0 & – & & – & \\ \hline \end{tabular}
\end{table}
Table 1: Layer structure from the available borehole information.  
These sedimentary and eruptive deposits lie on Mesozoic bedrock, sometimes composed of Cretaceous marl and sometimes of Jurassic petite and sandstone [13]. Both formations outcrop to the north and east of the town. However, the exact nature of the bedrock in the city of Ain T\(\acute{\text{e}}\)mouchent is not clear.