Soil Gas Investigations in Hatay‐Reyhanlı (Türkiye): Implications for Buried Fault Detection and Seismic Hazard Assessment

Abstract This study presents a soil gas geochemical survey in the Kırcaoğlu and Reyhanlı regions of Hatay Province, southeastern Türkiye, following the 2023 Kahramanmaraş earthquake doublet. The aim was to identify concealed faults and assess seismic hazard through analysis of soil CO 2 flux, CO 2 and 222 Rn concentrations, and carbon and helium isotopic compositions. A total of 98 sites were surveyed, and graphical statistical methods were used to establish geochemical anomaly thresholds. In Kırcaoğlu, two prominent gas anomaly zones were delineated with dominant NW‐SE and NE‐SW trends, likely representing buried faults linked to the Yesemek Segment, including one beneath the Reyhanlı Dam. In Reyhanlı, an east‐west gas anomaly suggests a possible westward extension of the Reyhanlı Fault. These findings refine the region's structural framework and highlight seismic risks from buried faults. Isotopic analyses show CO 2 derives from biogenic and deep crustal reservoirs, with 4 He/ 20 Ne and 3 He/ 4 He ratios confirming up to 7.1% crustal helium and