Yüce1,4, G., Italiano2,3, F., D’Alessandro4, W., Fu5, C.C., Kahraman1, B., Kürkcüoglu1, B., Yasin6, D., Elmacı7, H., İçhedef8, M., Gürboğa9, Ş., Demirtaş1, A., Özdemir1, A., Gülbay10, A.H., Akıllı11, H., Lin12, L.H., Wang13, P.L., Över14, S., Kılıç15, T.
1Department of Geological Engineering, Hacettepe University, Ankara, Türkiye.
2OGS, Sgonico, Italy.
3Athanor‐Geotechsrls, Rome, Italy.
4Istituto Nazionale di Geofisicae Vulcanologia (INGV), Palermo, Italy.
5Academia Sinica, Institute of Earth Sciences, Taipei, Taiwan.
6Department of Geological Engineering, Eskişehir Osmangazi University, Eskişehir, Türkiye.
7Department of Geological Research, General Directorate of Mineral Research and Exploration (MTA), Ankara, Türkiye.
8Ege University, Institute of Nuclear Sciences, Izmir, Türkiye.
9Department of Geological Engineering, Faculty of Mines, İstanbul Technical University, Istanbul, Türkiye.
10Türk Altın A.Ş., Ankara, Türkiye.
11General Directorate of Mineral Research and Exploration, Occupational Health and Safety Coordination, Ankara,Türkiye.
12Department of Geosciences, National Taiwan University, Taipei, Taiwan.
13Instituteof Oceanography, National Taiwan University, Taipei, Taiwan.
14Department of Civil Engineering, İskenderun Technical University, Hatay, Türkiye.
15Ministry of Interior, Disaster and Emergency Management Authority (AFAD), Ankara, Türkiye.
Abstract: The 6 February 2023 Kahramanmaraş earthquake doublet in Türkiye–Syria underscored the critical need to integrate geochemical monitoring into earthquake science. This study presents an interdisciplinary assessment of fluid and gas geochemistry along active segments of the East Anatolian and Dead Sea Fault Zones, with emphasis on post-seismic processes in the Hatay region. Hydrogeochemical and isotopic data from waters and gases reveal a fault-controlled degassing system linking the lithospheric mantle to shallow crustal environments.
The results indicate a dual end-member mixing between atmospheric N₂-rich gases and deep CO₂-rich fluids enriched in mantle-derived helium (R/Ra up to 5.95), evidencing active vertical migration pathways. Spatial clustering of mantle signatures along the Erzin–Reyhanlı corridor coincides with zones of increased Coulomb stress following the 2023 earthquakes, suggesting permeability enhancement consistent with fault-valve behavior.
Time-series observations of dissolved radon (Rn) and helium isotopes (³He) reveal systematic and diagnostically important variations. Radon concentrations increased notably in samples along the East Anatolian Fault Zone (e.g., ELM, HCL, KÖS) and more prominently along the North Anatolian Fault Zone (CTK, KYN) during the September 2024 campaign, likely linked to contemporaneous seismic activity. In contrast, ³He concentrations decreased at key sites (e.g., KYN, CTK, CIP), producing a marked decline in ³He/Rn ratios over time. This inverse correlation between radon and mantle-derived helium reflects contrasting depth sensitivities and responses to stress and rupture processes: radon increases are attributedto enhanced micro-fracturing and water–rock interaction in the upper crust, whereas mantle helium signals may be diluted or masked by increased crustal helium contributions under elevated stress conditions. Such behavior is consistent with pre-seismic and post-seismic gas response models and supports the use of ³He/Rn ratios as sensitive indicators of evolving fault permeability and stress regimes.
Carbon isotope data further constrain volatile origins, indicating mixed magmatic–metamorphic CO₂ sources and thermogenic–microbial CH₄ contributions. Soil gas anomalies delineate concealed fault structures and confirm the role of deep fluids in post-seismic crustal reorganization.
These findings demonstrate that integrated monitoring of fluid and gas geochemistry—particularly combined He–Rn systematics—provides a powerful tool for tracking fault activity, permeability evolution, and seismic hazard. Incorporating such datasets into earthquake preparedness frameworks can significantly improve the understanding of seismogenic processes and enhance resilience in tectonically active regions.
Acknowledgements:
This research has been funded by the TUBITAK project 123Y301 and by the Scientific Research Projects Coordination Unit of Hacettepe University under grant number 21551.
Keywords: Earthquake, gas geochemistry, East Anatolian Fault Zone, North Anatolian Fault Zone, Dead Sea Fault Zone, helium, radon, soil gas.
Yüce, G., Male, Full Professor, Ph.D., mainly engaged in hydrogeological research. E-mail: galipyuce@gmail.com
