Geotechnical ınsights from on-site ınvestigations of the 2023 Pazarcık–Elbistan Earthquake Sequence in Kahramanmaraş, Türkiye

Abstract This study aims to investigate the geotechnical effects of the February 6, 2023 Kahramanmaraş–Pazarcık (Mw 7.8) and Elbistan (Mw 7.6) earthquake sequence in the regions of Gölbaşı (Adıyaman), İskenderun, Demirköprü (Hatay), and Türkoğlu (Kahramanmaraş). Within the scope of the research, strong ground motion records obtained from AFAD stations were analyzed and compared with the EL-1 and EL-2 design spectra of the Turkish Building Earthquake Code (TBEC 2018). In addition, liquefaction susceptibility and cyclic softening mechanisms in fine-grained soils were evaluated using data from 53 microzonation boreholes in Gölbaşı. The results indicate that spectral accelerations in Hatay exceeded the design values, particularly at long periods, due to basin amplification and near-fault effects, and that widespread geotechnical damage such as sand ejecta, lateral spreading, and foundation settlements occurred across the region. Analyses specific to Gölbaşı further confirm high liquefaction susceptibility (FS < 1) and deformations in clayey units associated with cyclic softening. Overall, this study highlights the critical influence of local soil conditions on seismic demand and recommends that TBEC 2018 be improved to incorporate basin and near-fault corrections as well as mandatory cyclic softening checks for saturated fine-grained soils.