PSI - Issue 78

Yavuz Yadim et al. / Procedia Structural Integrity 78 (2026) 1895–1902

1896

1. Introduction Over the past six decades, Turkey and Syria have experienced rapid urbanization and population growth, significantly expanding their residential building stock. In Turkey, most residential structures are reinforced concrete (RC) buildings, with 47% built after 2000 and 31% built between 1981 and 2000. National statistics estimate 10–12 million buildings and over 25 million housing units, with around 6.5 million identified as structurally vulnerable due to outdated design, poor quality control, or lack of engineering oversight (EEFIT, 2024; TurkStat; Ministry of Environment and Urbanization, 2021; UN, 2014). On February 6, 2023, two powerful earthquakes struck southeastern Turkey and northern Syria. The first, Mw 7.8, occurred near Pazarcık in Kahramanmaras Province, followed by an event of M w 7.5 event near Elbistan. Both earthquakes ruptured the Eastern Anatolian Fault Zone, severely impacting cities, including Kahramanmaras, Adıyaman, Hatay, Osmaniye, and Gaziantep. Near the epicenter, Kahramanmaras transformed from a low-rise settlement to a dense urban area dominated by multistorey RC buildings.

Fig. 1. The city of Marash (today, Kahramanmaras) in Turkey has undergone dramatic transformation in its urban fabric. It shifted from a pattern of single-storey masonry and timber houses to reinforced concrete apartment buildings of 8 to 10 stories. Between 1910 and 2025, the population grew from approximately 50,000 to 570,000. The population remained around 50,000 inhabitants until 1960. (a) about 1910; (b) about 1995. Although the February 2023 earthquakes struck along the East Anatolian Fault Zone (EAFZ), much of Turkey's preparedness has historically focused on the North Anatolian Fault (NAF), due to the anticipated Istanbul earthquake. This sequence was particularly significant as it involved two independent high-magnitude mainshocks— Mw 7.8 and Mw 7.5, occurring less than 100 km apart within nine hours. Both events generated strong ground motions in the same urban areas, compounding the damage. Many buildings that survived the first quake collapsed during the second, including those expected to meet “life safety” or “collapse prevention” standards. Such sequential loading lies outside the standard seismic design assumptions, raising serious concerns about post-event structural performance (Bozkurt, 2001; Kaplan et al., 2008). The affected area covered a 400-km fault segment and included 10 major cities with over 15 million residents. Official reports indicate over 45,000 fatalities, more than 100,000 injuries, and 817,000 severely damaged or collapsed apartments among the 1.71 million buildings assessed, displacing an estimated 3 to 9 million people (EEFIT, 2024; AFAD, 2023). This study analyzes both earthquakes using strong-motion data from AFAD and investigates key causes of damage based on field observations from the disaster zone. Kahramanmaras Province, in southeastern Turkey, lies within a high-risk seismic zone along the East Anatolian Fault Zone (EAFZ) (Fig. 1). The region has experienced several moderate-to-strong earthquakes, and studies before the 2023 disaster warned of a large earthquake, estimating magnitudes of 6.5 or higher (Palutoglu & Sasmaz, 2017; Kalafat et al., 2021). Although these estimates underestimated the February 2023 events, they highlighted increasing vulnerability due to urban growth and aging infrastructure. Although national regulations promote earthquake-resistant design and contingency planning, their practical effectiveness has been inconsistent (Ambraseys, 2009). The EAFZ, a major left-lateral strike-slip fault marking the boundary between the Anatolian and Arabian Plates, extends 500– 700 km from the Karlıova Triple Junction to the Iskenderun Gulf. It comprises multiple fault segments with a well-documented history of seismicity, making it one of the region’s most hazardous active fault systems (Altunsu et al., 2023; Yılmaz et al., 1993, 1998). Recent studies have significantly advanced our understanding of the seismicity and hazard potential of the Kahramanmaras region and East Anatolian Fault Zone (EAFZ). Vavra et al. (2025) reported that earthquakes ruptured multiple EAFZ segments with a long history of seismicity, indicating a