Role of soil type in geotechnical damage observed in Gölbaşı during the 2023 Türkiye earthquake sequence.

This study presents an assessment of geotechnical damage observed in Gölbaşı District in the Adıyaman Province after the southeastern Türkiye earthquake sequence on February 6, 2023. Preliminary reconnaissance indicated the presence of soil ejecta with a plasticity index typically higher than nine, questioning the role of flow liquefaction during these events. Detailed observations revealed various types of damage, including major ground settlements up to 60 cm near several buildings, substantial cracks in highway sections, undulations in railway tracks, and observable fissures on roads and pavements. Given the predominance of plastic soils underlying the city center and the malfunction of strong motion station 0208 in Gölbaşı, the underlying cause of such widespread damage remains a complex phenomenon. Therefore, to unravel the principal cause of damage, this study conducted a detailed analysis of the geotechnical properties of soils. An extensive laboratory testing program, in combination with original interpretation of in-situ tests performed before and after the earthquake sequence enabled accurate characterization of properties of the underlying soil profile. The primary factors contributing to the extensive geotechnical damage in Gölbaşı are identified along with the main failure mechanisms, focusing on the role of cyclic softening of the predominantly fine-grained soils rather than flow liquefaction.