Quantifying the Contribution of Multiple Earthquakes to Seismic Damage in RC Buildings: Analysis of the Kahramanmaras Earthquake Sequence

The consideration of consecutive seismic events remains a notable deficiency within current seismic design practices for engineering structures. The progressive accumulation of damage from an earthquake sequence poses a significant risk to the structural integrity of buildings, even those designed to exhibit ductile seismic behavior. The Kahramanmaras earthquake sequence in 2023 presented a unique opportunity to evaluate the contribution of multiple earthquakes on seismic damage in reinforced concrete (RC) buildings. The primary objective of this research is to quantify the variation in structural damage within low- to mid-rise RC buildings as a result of consecutive seismic events occurring within a short time period. Utilizing recorded ground motions and representative numerical models for RC buildings, the incremental damage sustained by RC building typologies subjected to the Kahramanmaras earthquake sequence is analyzed. This study examines the incremental increase in the probability of reaching predefined damage levels, comparing the effects of the first event alone with those of the complete earthquake sequence. The results demonstrate a significant contribution of subsequent events to structural damage accumulation, increasing overall collapse rates by approximately 2% on average, with the most severe impact observed in low code-compliant buildings where up to 9.2% of moderately damaged structures progress to collapse. Furthermore, conditional damage transition probabilities are derived, establishing a Bayesian updating framework to recalibrate post-sequence empirical fragility curves for single-event assessments.