## 1 Introduction  
The Eskisehir Basin is a disaster-prone area due to the earthquake hazard, non-earthquake-resistant buildings, and local ground conditions [1]. Seismic hazard analyses have been investigated in previous studies, and seismic hazard maps have been produced using the locations of earthquake that occurred between 1900 and 2019. The lengths of active faults in the region were then determined, along with the earthquake magnitudes that could be generated by those faults in order to assess the earthquake hazard in the study area [2]. The Eskisehir Fault Zone (EFZ) in the study area is one of the internal fault zones of the Anatolian Plate [3; 4; 5; 6]. It is closely related to the Eskisehir Basin [7; 8; 9]. The locations of active segments in the EFZ, and the source of the Ms 6.4 magnitude earthquake that occurred on 20 February 1956 (one of the main seismic events in the region), have been discussed in detail in the literature [4; 8; 10; 11; 12]. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [11], in one of the most recent studies conducted in the region, found that the Cukurhisar-Sultandere fault segment passes to the south of Eskisehir city center and is considered to be one of the important earthquake sources in the region. Liquefaction and soil amplification are the leading earthquake-related risks that are features of the region. To further support the structural geology and reveal seismic risks in Eskisehir, Graben gravity measurement points of five lines, each starting with a southernmost station, have been planned (Figure 1a). Eskisehir city center is rated as high to moderate with regard to soil amplification and liquefaction hazards [1] (Figure 1b). The study area mainly consists of old and new alluvium, which is bounded by hard rocks (limestone, conglomerate, ophiolitic melange, and marble) in the north and south [11; 13; 14] (Figure 1b). Figure 1: **(a)** A general map of gravity measurement locations in study area. (**b**) A map showing areas at risk for liquefaction and soil amplification: Zone A (high seismic risk); high population ratio and high seismic hazard, Zones B and C (medium seismic risk); lower population ratio and high seismic hazard, Zone D (low seismic risk); extremely low population ratio and very high seismic hazard [1] and gravity measurement locations in Eskisehir City Center (datum: WGS84 UTM Zone 36 N). Determination of active fault locations in the region is extremely important in terms of earthquake hazard assessment. It has been seen in previous studies that gravity measurements produce successful results in determining horizontal discontinuities [15; 16; 17; 18; 19; 20; 21]. Bouguer gravity anomaly maps also reveal information regarding plunging or vertical lateral boundaries between rock units. Detected boundaries are generally interpreted as horizontal discontinuities of features, such as geologic contacts, faults, or horsts/grabens. The most important purpose of the edge detection analysis of this study is to detect such discontinuities, which are usually masked in Bouguer maps. The fault locations, which can be revealed by two-dimensional edge detection, provide significant additions for later seismic reflection and paleoseismology studies. In addition, the Bouguer gravity anomaly map obtained in the study area, a region rich in geothermal resources, will contribute to preliminary evaluations to be made within the scope of geothermal exploration [22; 23; 24; 25; 26]. The aim of this study is to carry out edge detection of data collected in the field by gravity measurements to reveal the fault structures that form the Eskisehir Graben (Figure 1a). Previous studies in the region have used a variety of methods, such as geological observation, boreholes, seismic reflection and microtemors, to reveal the structural geology of the Eskisehir Basin [4; 11; 27; 28].