Amplification can occur in a graben as a result of strong earthquake-induced ground motion. Thus, in seismic hazard and seismic site response studies, it is of the utmost importance to determine the geometry of the bedrock depth. The main objectives of this study were to determine the bedrock depth and map the depth-to-bedrock ratio for use in land use planning in regard to the mitigation of earthquake hazards in the Eskişehir Basin. The fundamental resonance frequencies (f_r) of 318 investigation sites in the Eskişehir Basin were determined through case studies, and the 2-D S-wave velocity structure down to the bedrock depth was explored. Single-station microtremor data were collected from the 318 sites, as well as microtremor array data from nine sites, seismic reflection data from six sites, deep-drilling log data from three sites and shallow drilling log data from ten sites in the Eskişehir Graben. The fundamental resonance frequencies of the Eskişehir Basin sites were obtained from the microtremor data using the horizontal-to vertical (H/V) spectral ratio (HVSR) method. The phase velocities of the Rayleigh waves were estimated from the microtremor data using the spatial autocorrelation (SPAC) method. The fundamental resonance frequency range at the deepest point of the Eskişehir Basin was found to be 0.23–0.35 Hz. Based on the microtremor array measurements and the 2-D S-wave velocity profiles obtained using the SPAC method, a bedrock level with an average velocity of 1300 m s⁻¹ was accepted as the bedrock depth limit in the region. The log data from a deep borehole and a seismic reflection cross-section of the basement rocks of the Eskişehir Basin were obtained and permitted a comparison of bedrock levels. Tests carried out using a multichannel walk-away technique permitted a seismic reflection cross-section to be obtained up to a depth of 1500–2000 m using an explosive energy source. The relationship between the fundamental resonance frequency in the Eskişehir Basin and the results of deep drilling, shallow drilling, shear wave velocity measurement and sedimentary cover depth measurement obtained from the seismic reflection section was expressed in the form of a nonlinear regression equation. An empirical relationship between f_r, the thickness of sediments and the bedrock depth is suggested for use in future microzonation studies of sites in the region. The results revealed a maximum basin depth of 1000 m, located in the northeast of the Eskişehir Basin, and the SPAC and HVSR results indicated that within the study area the basin is characterized by a thin local sedimentary cover with low shear wave velocity overlying stiff materials, resulting in a sharp velocity contrast. The thicknesses of the old Quaternary and Tertiary fluvial sediments within the basin serve as the primary data sources in seismic hazard and seismic site response studies, and these results add to the body of available seismic hazard data contributing to a seismic microzonation of the Eskişehir Graben in advance of the severe earthquakes expected in the Anatolian Region.

The Eskişehir Fault Zone is one of the major neotectonic structures of Turkey, extending from İnegöl (Bursa) to Cihanbeyli (Konya). The fault zone presents a considerable seismic risk for the city of Eskişehir but the exact locations of active segments and the source of the major seismic event, the 1956 earthquake (M = 6.5) that occurred in the instrumental period (from 1900 to 2013), have been debated in recent literature. The structural data obtained from field studies indicate an approximately N60W-trending main strand of the right lateral strike-slip Eskişehir Fault Zone. This trend corresponds to the en echelon bends on the course of the Sarısu River. Using this concurrence, the positions of Bahçehisar and the Çukurhisar-Sultandere segments are proposed and checked by seismic reflection studies. The seismic sections disclosing positive flower structures confirm the hypothesized position of the Çukurhisar-Sultandere segment. The relocation of epicenters and focal mechanism solutions of seismic events in 1956, 1990, 2010, and 2013 indicate that the Çukurhisar-Sultandere segment might be the rupture source of the 1956 event and is a possible potential seismic source for an earthquake that could seriously affect the Eskişehir settlement.

A large part of the residential areas in Turkey are at risk from earthquakes. The main factors that threaten residential areas during an earthquake are poor quality building stock and soil problems. Liquefaction, loss of bearing capacity, amplification, slope failure, and landslide hazards must be taken into account for residential areas that are close to fault zones and covered with younger sediments. Analyzing these hazards separately and then combining the analyses would ensure a more realistic risk evaluation according to population density than analyzing several risks based on a single parameter. In this study, an integrated seismic risk analysis of central Eskişehir was performed based on two earthquake related parameters, liquefaction and amplification. The analysis used a simple weighting method. Other earthquake-related problems such as loss of bearing capacity, landslides, and slope failures are not significant for Eskişehir because of the geological and the topographical conditions of the region. According to the integrated seismic risk analysis of the Eskişehir residential area, the populated area is found to be generally at medium to high risk during a potential earthquake.

On 06 February 2023, two strong earthquakes occurred in Kahramanmaraş, Türkiye. The first earthquake with a moment magnitude (Mw) of 7.7 and an epicenter in Pazarcık, was followed by a second earthquake with a moment magnitude of (Mw) 7.6 and an epicenter in Elbistan. These earthquakes have caused catastrophic life and structural loss in ten cities where more than 15 million people permanently live. Concentrating on the epicenter of the second earthquake, Elbistan, this study investigates the main characteristics of the earthquakes and the failure of the reinforced concrete buildings. Acceleration records from both earthquakes were analyzed and site surveys were conducted to evaluate the caused damages. The high number of completely collapsed buildings highlighted the vulnerability of the general old building stock constructed before 2000. Notably, unlike previous earthquakes in Türkiye, these earthquakes also affected new buildings constructed according to the recent Turkish Earthquake Code. In that respect, seismic damages seen in these buildings are presented and interpreted in this paper. To validate the observed deficiencies, a damaged building whose construction had just been completed but not yet occupied was both surveyed on site and subjected to non-linear performance analyses. The analysis results demonstrated that the damage distribution and locations in the models closely matched the observed damage after the earthquakes. In addition, the analyses also revealed the effect of brick infill walls on the building’s seismic behavior.