## 3 Earthquake Distribution in the Study Area  
The aim of this section is to review all of the historical and instrumental earthquakes in the Eskisehir region, between 1900 and 2019, to determine the earthquake density within the Eskisehir Province and also to delineate the regions characterized by earthquakes of different depths. A map was generated for that purpose using ArcGIS 10.5; An Earthquake Density Map of Eskisehir (1900-2019) (Figure 2a). Earthquake data from the years 1900-2019 were downloaded from the KOERI (Kandilli Observatory and Earthquake Research Institute) web portal (url-1: [[http://www.koeri.boun.edu.tr/sismo/zeqdb/](http://www.koeri.boun.edu.tr/sismo/zeqdb/)]([http://www.koeri.boun.edu.tr/sismo/zeqdb/](http://www.koeri.boun.edu.tr/sismo/zeqdb/)) accessed on 8 March 2022). During the downloading, all of the parameters were selected as accurately as possible with coordinated boundaries to cover the Eskisehir Province for earthquakes with magnitudes greater than 3. There were 161 earthquakes in total with magnitudes of greater than 3 that occurred within the study area within the selected time span. The result of the analysis shows that most of the earthquakes with magnitudes between 3 and 6.4 occurred in the southern part of the Tepebasq District and the northern part of the Odunpazam District. The earthquake occurrence is attributed to faults, because most of the earthquake epicenters are distributed between active faults. Generally, the northwest regions of the Eskisehir Province are characterized by a high density of earthquakes, and the center and southwest regions are accompanied by moderate numbers of earthquakes, while the northeast and east parts are characterized by a low density of earthquakes. This distribution has a high correlation with active faults, as the regions with high earthquake density are also occupied by active faults (Figure 2a). As shown in Figure 2, the EFZ trends from northwest to southeast, and most of the earthquake epicenters are located within that zone. The faults have parallel distribution to the fault zone orientation. To find the dip of the Eskisehir Fault Zone, the earthquake hypocenters first were located by finding the distance of the earthquake epicenters from the fault zone and their depths below the surface. The average distance between the earthquake points and the zone was calculated and found to be about 9 km. The average depth of  
Figure 2: (**a**) An earthquake density map showing the distribution of earthquakes from 1900–2019. (**b**) Schematic graphics of earthquake focal points along the EFZ in the Eskisehir Graben [36] ( datum: WGS84 UTM Zone 36 N). earthquakes that have occurred around the fault is between 5 and 10 km. The dip of the EFZ was calculated graphically and is shown in Figure 2b. The result of the calculation shows the EFZ to be dipping about 35\({}^{\circ}\) to the northeast. The seismicity map of the study area and its surroundings and the location of the 20 February 1956 (Ms 6.4) Eskisehir earthquake are presented in Figure 2a. In all, 3499 houses, 10 schools, 15 mosques, and 3 official buildings were demolished, along with 1303 barns and haystacks in that particular earthquake in Eskisehir city center. In the 17 August 1999 Kocaeli (Mw 7.4) earthquake, which was centered approximately 250 km from Eskisehir city center, 86 people lost their lives in the city of Eskisehir, and 95 people were injured. In addition, 70 houses/workplaces suffered severe damage, 1 building collapsed during the earthquake, and 4 buildings collapsed after the earthquake [37]. According to the AFAD (Disaster and Emergency Management Authority) 2018 Earthquake Hazard Map of Turkey, the highest ground acceleration that can be encountered in the study area, with a 10% probability of exceedance within 50 years (return period of 475 years), is determined to be 0.29 G (url-2: [[https://tdth.afad.gov.tr/](https://tdth.afad.gov.tr/)]([https://tdth.afad.gov.tr/](https://tdth.afad.gov.tr/)) accessed on 8 March 2022).