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Abstract

Abstract: The temporal and spatial variations of radon in groundwater in a selected area at the western part of the North Anatolian Fault Zone are investigated. This study is carried out in the framework of the German-Turkish Project on Earthquake Prediction Research, aimed at demonstrating the ability for detecting precursors to earthquakes. Since 1987 intensive mapping of radon in groundwater was carried out and supplemented by hydro chemical studies. Discrete water samples were taken from more than 570 springs and wells. Repeated measurements were carried out semi-annually at about 100 sites. Temporal variations of radon in groundwater are correlated with groundwater discharge with maximum values in spring. The spatial distribution of radon in groundwater is roughly related to the radio-element content of the geological formations, but nevertheless shows significant variations within a formation. The highest radon concentrations are found in spring waters from granites aquifers and low concentrations are related to limestone, marble, amphibolites and greenstone. Springs with the highest Rn-222 contents (standardised with respect to the aquifer geology) follow the East-West striking fault system. Contrary to the majority of springs showing annual variations, 18 springs out of 99 are characterised by a continuous Rn-222 increase from autumn 1987 until autumn 1989. These springs are located in the western part of the investigation area marking the main fault for about 20 km but then striking to South-West following a formerly active branch of the North Anatolian Fault Zone possibly indicating its reactivation.