Pre-earthquake hydrogeochemical anomalies in spring waters: two distinctive cases from western Türkiye

In earthquake sciences, identifying reliable earthquake precursors remains a challenge, requiring systematic multi-disciplinary approach and monitoring. This study investigates hydrogeochemical anomalies preceding moderate-magnitude (Mw 5) earthquakes by analyzing natural spring waters. Five spring water sites have been investigated thus monitoring was conducted for the Mw 5.0 Mudanya earthquake (December 4, 2023) in the Marmara region and the Mw 5.0 Kuşadası earthquake (January 27, 2024) in the Aegean Extensional Province (AEP), focusing on electrical conductivity (IC) and ion concentrations (Cl⁻, SO₄²⁻, Na⁺, K⁺, Mg²⁺, Ca²⁺). Distinct EC and ion anomalies (lasting for at least 30 days) were observed at the Sap-01 and Naz-01 sites before the earthquakes, in Marmara region and AEP, respectively, suggesting a potential link to pre-seismic crustal deformation and possible mixing with thermal waters. In contrast, no significant anomalies were detected in samples collected from two springs in Marmara (İst-01, Brs-01), and AEP (Çine-01), likely due to their off-fault locations or placement on different tectonic blocks. These findings highlight the importance of geological knowledge in selecting sampling sites for geochemical monitoring. Results suggest that spring water anomalies could serve as potential earthquake precursors. Further multi-disciplinary studies integrating seismological, geodetic, and geochemical data, along with long-term, high-resolution continuous monitoring networks, are essential to better understand these pre-earthquake signals.