Effects of seismic activity on groundwater level and geothermal systems in İzmir, Western Anatolia, Turkey: the case study from October 30, 2020 Samos Earthquake

Abstract

The October 30, 2020 Samos earthquake (Mw 6.6) affected the Aegean Sea and environs, caused destruction and loss of life in the city of İzmir located 70 km away from the earthquake epicenter. Before this earthquake, water resources were monitored in the areas of Bayraklı, Gülbahçe, and Seferihisar. For this purpose, 10 groundwater monitoring wells were drilled in the Bayraklı area, where groundwater level, temperature, and electrical conductivity changes were monitored at 1-h intervals in 5 wells. Besides physical parameters such as groundwater levels, temperatures and electrical conductivities, hydrogeochemical cations, and anions measured in the study area. Change in the groundwater levels was observed before, during, and after the Samos earthquake. A trend of rising groundwater level was observed two days before the mainshock, to a height of 10 cm, and the level was maintained till the end of the earthquake. The water levels returned to its original height after about 7 to 10 days of the earthquake. Moreover, electrical conductivity (EC) values were changed because of the interaction with the surrounding rocks and well walls, mixing with different waters during the earthquake shaking. The essential anomalies were observed in the geothermal fields of Gülbahçe and Seferihisar. Due to this earthquake, new geothermal springs emerged along the NE-SW trending Gülbahçe and Tuzla faults, located about 50 to 20 km from the Samos earthquake epicenter, respectively. The new geothermal waters are in Na-Cl composition and similar to other geothermal springs in the region. While the recorded water temperatures in the new geothermal springs vary from 40 to 45 °C in Seferihisar, it was measured between 35 and 40 °C in Gülbahçe. Due to these anomalies, it is found essential to monitor the effect of the earthquake on the physical and chemical characteristics of the groundwater and its usefulness in earthquake predictions.

The Uncertain Certainty of a Nightmare: What If Another Destructive Earthquake Strikes Izmir (Türkiye)?

“…Numerous buildings collapsed or sustained damage. This earthquake event, recorded at VI-VII levels on the Mercalli intensity scale (Figure 1a,b), highlighted the potential for mass movements and liquefaction at considerable distances from the epicenter, in addition to surface wave amplification and surface faulting, much like the Kahramanmaraş earthquakes in 2023 [10,45]. Various regions within Izmir experienced such phenomena during the Samos earthquake, with noticeable signs of liquefaction, particularly along the coastlines (Figure 1c,d).…”

“…The areas affected by seawater intrusion were previously locations of streambeds [45]. Conversely, the reduction in damage on solid ground north of Bayraklı indicates the influence of soil properties.…”

“…Izmir has a history of enduring numerous earthquakes within its provincial boundaries and in neighboring areas like Manisa, Aydın, Balıkesir, Izmir Bay, and the surrounding islands such as Samos, Lesvos, and Chios [45]. Historical earthquake records indicate multiple instances centered in Manisa, Selçuk-Efes, Foça, Turgutlu, Menemen, and Çeşme, estimated to fall within the VIII-X intensity range on the Modified Mercalli Scale [46].…”

“…Damaged and collapsed building data digitalized from the earthquake damage assessment studies of the Ministry of Environment and Urbanization of the Republic of Türkiye, the Samos earthquake reports, and findings in the field studies of Authors [45,52]. Buildings were obtained by the Urban Planning Department of the ˙Izmir Metropolitan Municipality.…”

“…Hydrogeological data derived from different sources such as observation wells [45], the literature reports, and groundwater level iso-depth contours (only for Quaternary units) interpolated from these data via ArcGIS PRO software (ver. 3.2.1).…”