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

Taygun Uzelli̇,Esra Bi̇lgi̇ç,Alper Baba,Orhan Tatar,Bahadır Öztürk,Hasan Sözbi̇li̇r

doi:10.3906/yer-2101-9

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.

Highlights

Seismic disturbances can cause damages to the earth’s crust and affect the physical and chemical characteristics of groundwaters and geothermal waters
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
Groundwater level changes in the area of Bayraklı In Bayraklı, buildings on Holocene alluvial deposits saturated with groundwaters were seriously affected after the Samos earthquake, and 17 buildings collapsed

Summary

Introduction

Seismic disturbances can cause damages to the earth’s crust and affect the physical and chemical characteristics of groundwaters and geothermal waters. Pre-earthquake changes in physical, chemical, and isotopic properties, different events with mechanisms affecting the post-earthquake water quality are taken as a basis. Post-earthquake events include strain/rupture of faults (Cotecchia et al, 1990; Yan et al, 2016; Petitta et al, 2018), near-surface deformations (Pasvanoglu et al, 2004; Charmoille et al, 2005), dilation and mixing of different aquifers (Poitrasson et al, 1999), the release of geothermal waters (Barberio et al, 2017) and gases (Favara et al, 2001; Chiodini et al, 2004; Italiano et al, 2004; Ciarletti et al, 2016)

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