Seismic Performance of Idealised RC Buildings Under Topographically Amplified Ground Motion: Site-Specific Evidence from the 2023 Kahramanmaraş Earthquake in Adana

The Mw7.7 Pazarcık–Kahramanmaraş and Mw7.5 Elbistan–Kahramanmaraş earthquakes on 6 February 2023 caused the collapse of 11 buildings in Adana’s city centre—predominantly 15-storey RC structures in a narrow zone—despite peak ground accelerations of only 0.05 g; most collapses occurred during the Mw7.7 event. Two-dimensional seismic site response analyses at the site of interest with bedrock input from station TK0118 yielded topographic amplification factors of 2.37 (EW) and 2.09 (NS) for homogeneous conditions; with stratigraphic heterogeneity, NS increased to 2.66 and EW remained at 2.27, reaching above 3.0 at the slope crest. Spectral amplification factors reached 4.53 (NS, T = 0.90 s) and 3.21 (EW, T = 0.68 s), indicating amplification in the short-to-intermediate period range. These amplified records were applied to idealised 15-storey RC models—from code-compliant to deliberately deficient—with C16 and C8 concrete classes through nonlinear performance analyses. Under unamplified TK0118 records, no model reached collapse-level damage. Under amplified records, only the most deficient model exhibited widespread shear and strain failures in the lower storeys. A detected velocity pulse (Tp = 13.496 s) was excluded as a collapse mechanism, as its period far exceeds structural periods (1.2–1.9 s). The collapses are attributable to the compounding of topographic and stratigraphic amplification with pre-existing structural deficiencies.