ICCESEN 2017 The measurement of soil gases and shallow temperature for determination of active faults in a geothermal area: a case study from Ömer–Gecek, Afyonkarahisar (West Anatolia) Ahmet Yıldız 1 & Can Başaran 1 & Metin Bağcı 1 & Ayla Gümüş 2 & Feyzullah Ekrem Çonkar 3 & Yusuf Ulutürk 4 & Hüseyin Ali Yalım 2 Received: 20 November 2017 /Accepted: 1 April 2018 # Saudi Society for Geosciences 2018 Abstract Afyonkarahisar is a very important geothermal province of western Anatolia and has low and medium enthalpy geothermal areas. This study has been carried out for the preparation of distribution maps of soil gases (radon and carbon dioxide) and shallow soil temperature and the exploration of permeable tectonic regions associated with geothermal systems and reveal the origins of radon and carbon dioxide gases. The western district of the study area is characterized by the high radon concentration (168.30 kBq/ m 3 ), carbon dioxide ratio (0.30%), and soil temperature (21.0 °C) values. Fethibey and Demirçevre faults, which allow the circulation of geothermal fluids, have been detected in the distribution maps of radon, carbon dioxide, and shallow depth temperature and the directions of the curves in these maps correspond to the strikes of Demirçevre faults. The effect of the fault plays an important role in the change of carbon dioxide concentration along the W-E directional geological section prepared to determine the change of soil gas and shallow depth temperature values depending on lithological differences, fault existence, and geothermal reservoir depth. On the other hand, it was determined that Rn 222 concentration and soil temperature changed as a function of geothermal reservoir depth or lithological difference. Tuffs in Köprülü volcano-sedimentary units are the main source of radon due to their higher uranium contents. Besides, the carbon dioxide in Ömer–Gecek soils has geothermal origin because of the highest carbon dioxide content (99.3%) in non-condense gas. The similarities in patterns of soil temperature, radon, and carbon dioxide indicate that the variation in soil temperatures is related to radon and carbon dioxide emissions. It is concluded that soil gas and temperature measurements can be used to determine the active faults in the initial stage of geothermal exploration successfully. Keywords Radon . Carbon dioxide . Soil temperature . Geothermal . Manifestations . Ömer–Gecek . Afyonkarahisar Introduction Geothermal energy is the natural heat stored in the earth’ s crust. This energy induces a raise in heat anomaly of the crust by means of intruded magma in the crust. Fumaroles, hot resources, and heated and weathered areas are the most im- portant surface manifestations of the geothermal resources and these are also the windows to the underlying geothermal re- sources (Steingrimsson 2009). In the geothermal energy study, it is aimed at collecting important data related to geothermal systems such as reservoir rock, heat source, cap rock, and faults and exploring the ex- ploitable geothermal energy resource. In the preliminary phases of the exploration, cheap and fast methods are used in large study areas. The dimensions of the study area are This article is part of the Topical Collection on Geo-Resources-Earth- Environmental Sciences * Ahmet Yıldız ayildiz@aku.edu.tr 1 Engineering Faculty, Department of Geological Engineering, Afyon Kocatepe University, Afyonkarahisar, Turkey 2 Physics Department, Afyon Kocatepe University, Afyonkarahisar, Turkey 3 Center of Application and Research of Geothermal-Mineral Water and Ore Deposits, Afyon Kocatepe University, Afyonkarahisar, Turkey 4 AFJET, Afyon Geothermal and Tourism Incorporated Company, Afyonkarahisar, Turkey Arabian Journal of Geosciences (2018) 11:175 https://doi.org/10.1007/s12517-018-3520-8