The town of Aigion lies on the south side of the graben of the Corinth Gulf, towards the West. This graben -together with the Rio and Patras grabens- forms a 140 km long and 40 km wide rift which separates the Pre-Neogene folded basement of Sterea Hellas and the
Peloponnese. The geological Pre-Neogene basement of the greater area comprises Mesozoic limestones and flysch. The Meta-alpine geological structure (syn-rift sediments) consists of three lithostratigraphic units. The lower one consists of thick layers of very stiff clays, marls and very dense sands, deposited from Upper-Pliocene to Lower-Pleistocene. The middle one comprises Quaternary deltaic and alluvial fan deposits, mostly conglomerates, with a thickness of about 100–150 m. Finally, the topmost unit comprises Holocene alluvial fan deposits (gravel, sands, silts and clays) of variable thickness, upon which the city is founded (e.g., Athanasopoulos et al., 1999; Apostolidis et al., 2006).