Effects of Seismic Activity on Groundwater Level and Geothermal Systems in İzmir,\rwestern 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\rlife in the city of İzmir located 70 km away from the earthquake epicenter. Before this earthquake, water resources were monitored in\rthe areas of Bayraklı, Gülbahçe, and Seferihisar. For this purpose, 10 groundwater monitoring wells were drilled in the Bayraklı area,\rwhere groundwater level, temperature, and electrical conductivity changes were monitored at 1-h intervals in 5 wells. Besides physical\rparameters such as groundwater levels, temperatures and electrical conductivities, hydrogeochemical cations, and anions measured\rin the study area. Change in the groundwater levels was observed before, during, and after the Samos earthquake. A trend of rising\rgroundwater level was observed two days before the mainshock, to a height of 10 cm, and the level was maintained till the end of the\rearthquake. The water levels returned to its original height after about 7 to 10 days of the earthquake. Moreover, electrical conductivity\r(EC) values were changed because of the interaction with the surrounding rocks and well walls, mixing with different waters during the\rearthquake shaking. The essential anomalies were observed in the geothermal fields of Gülbahçe and Seferihisar. Due to this earthquake,\rnew geothermal springs emerged along the NE-SW trending Gülbahçe and Tuzla faults, located about 50 to 20 km from the Samos\rearthquake epicenter, respectively. The new geothermal waters are in Na-Cl composition and similar to other geothermal springs in\rthe region. While the recorded water temperatures in the new geothermal springs vary from 40 to 45 °C in Seferihisar, it was measured\rbetween 35 and 40 °C in Gülbahçe. Due to these anomalies, it is found essential to monitor the effect of the earthquake on the physical\rand chemical characteristics of the groundwater and its usefulness in earthquake predictions.