Examination of the severe impact of the February 6, 2023 earthquakes on Antakya district considering pulse-like ground motions, supershear rupture, and basin effects

The first earthquake of the February 6 Kahramanmaraş sequence, with its epicenter in Pazarcık, caused severe damage and destruction in the Antakya/Hatay region. In addition to human factors such as structural design, construction practices, and inspection processes, the catastrophic outcomes were influenced by extraordinary seismic characteristics tied to the region's tectonics, geographic location, geological structure, and topographic features. The Antakya region has the potential to experience phenomena such as forward directivity, fling-step, supershear rupture, basin effects, and trampoline effects. This study analyzed records from strong ground motion stations in Antakya to investigate the signatures of these phenomena, both individually and in combination, providing a broader perspective compared to existing studies in the literature. Data from each station were evaluated based on the detection and orientation of velocity pulses, the shape of acceleration response spectra, Cumulative Absolute Velocity (CAV) values, Husid plots, and geological/topographic characteristics. The results revealed that some stations exhibited combined traces of forward directivity, supershear, and basin effects, while others displayed these effects individually. Additionally, heavy damage and destruction rates in neighborhoods surrounding each station were compiled. During the damage assessment, structures were categorized based on parameters such as building age, number of stories, and soil type. The findings showed a significant increase in heavy damage and destruction in cases where potential supershear, forward directivity, and basin effects occurred simultaneously. The use of the V_s,30-based soil classification and acceleration amplification approach was found to be inadequate in scenarios where basin and trampoline effects were likely. Furthermore, the discrepancy between the response spectra of the Turkish Building Earthquake Code 2018 (TBEC-2018) and station records can be attributed to pulse-like ground motions, supershear effects, and site amplifications. Therefore, it is crucial to consider these phenomena in the design and assessment processes for both newly constructed and existing buildings in regions where such effects are likely to occur.