Groundwater level anomalies as precursors to the february 6 double earthquake in Türkiye

Abstract On 2023 February 6, two major earthquakes occurred in close succession, constituting a rare double earthquake event that strongly affected 11 provinces of Türkiye. This study presents one of the first detailed analyses of real-time groundwater level responses to a double earthquake sequence, using high-frequency, continuously recorded water-level data from four monitoring wells in Hatay Province that were actively recording during the event. Variations in groundwater levels were examined to evaluate their relationship with seismic activity and to assess potential precursory behavior. The results reveal pronounced and heterogeneous responses among the wells despite their comparable geological settings and proximity to the fault zone. The largest fluctuation was observed in the Serinyol well, with a water-level change of 463 cm, followed by 58 cm in the Tigem well, 22 cm in the Mazmanlı well, and only 18 cm in the Erzin well, the latter attributed to its distinct geological structure. Notably, anomalous groundwater changes were detected 255 min prior to the earthquakes in the Serinyol, Tigem and Mazmanlı wells. These findings demonstrate that multi-well, real-time groundwater monitoring can capture pre-seismic signals even during complex double earthquake events, providing new methodological evidence for integrating hydrogeological observations into earthquake early warning and risk-mitigation frameworks.