Integration of geochemical data for detecting groundwater responses to geodynamic processes: a case study from Azerbaijan

Abstract

Background. Hydrogeochemical changes in groundwater are increasingly recognized as potential indicators of stress accumulation preceding earthquakes. However, reliable identification of short-term precursors requires long-term, instrument-based observations and integration of multiple datasets adapted to local geological and hydrogeological conditions. The Shamakhi–Ismayilli seismogenic zone in Azerbaijan, situated at the convergence of the Eurasian and Arabian plates, offers an excellent natural laboratory for studying hydrogeochemical manifestations of geodynamic activity. This research aims to identify groundwater anomalies that precede seismic events, quantify their temporal relationships to earthquake occurrence, and evaluate the effectiveness of integrated geochemical monitoring for early warning applications in the Caucasus region.

Methods. A multi-parameter observation network of seven self-flowing wells and springs was established across contrasting litho-hydrogeological environments. Systematic, time-stamped measurements were performed for pH, Eh, CO₃²⁻, HCO₃⁻, Σ(Cl,Br,I)⁻, SO₄²⁻, total hardness, Ca²⁺, Mg²⁺, Σ(Na,K)⁺, total mineralization, and Σ(Fe²⁺,Fe³⁺). Hydrogeodynamic parameters such as water level, temperature, discharge, and color were continuously recorded. Gas-geochemical monitoring focused on dissolved helium, while radiogeochemical control involved α-field measurements at reference sites. An anomaly index (A_an = K × X × Σ) was applied to identify significant deviations from seasonal background levels, enabling automated recognition of abnormal trends.

Results. Prior to the 18 January 2023 Shamakhi earthquake (Mpv 3.0; h=18 km), synchronous short-lived hydrogeochemical anomalies were observed. Sulfate concentrations (SO₄²⁻) increased from 440–480 to 640 mg/L, Σ(Na,K)⁺ decreased from 700–750 to 450 mg/L, and Σ(Cl, Br, I)⁻ dropped sharply from 630–660 to 60 mg/L. Total iron (Σ(Fe²⁺,Fe³⁺)) rose from 6–15 to 48 mg/L, while carbonate (CO₃²⁻) levels in the Chukhuryurd-49 well increased from 0 to 220 mg/L. Helium concentrations near the epicentral zone rose by almost an order of magnitude, later spreading throughout the network. In the Shamakhi-8 well, water level rose eight days before the shock and sharply declined three days prior, coinciding with darkening of the water.

Conclusions. The results confirm that site-specific, multi-parameter hydrogeochemical monitoring significantly improves the detection and interpretation of earthquake precursors. The nature and amplitude of anomalies are governed by structural position, hydrogeological regime, and focal depth. Integration of hydrogeochemical, hydrogeodynamic, gas, and radiogeochemical data with geodetic and microseismic observations enhances precursor reliability and reduces false-alarm rates. Such interdisciplinary monitoring frameworks can strengthen regional seismic hazard assessment and contribute to the development of an operational early-warning system for the broader Caucasus region.