Earthquake risk in reinforced concrete buildings during aftershock sequences based on period elongation and operational earthquake forecasting

Rapid post-earthquake damage assessment is critical to short-term earthquake crisis management. Reinforced concrete buildings may accumulate damage during an aftershock sequence, and short-term damage forecasts after the mainshock can aid in decision-making (in particular, on whether to allow immediate occupancy) before further damage actually occurs. This paper presents an operative damage forecasting and building tagging procedure for reinforced concrete buildings during synthetic aftershock sequences near Thessaloniki, Greece, for two hypothetical earthquake scenarios. The synthetic aftershock sequences are simulated, and the time-variant seismic vulnerability is modeled based on fragility curves for the damage state thresholds in terms of period elongation. Period elongation is chosen as a damage proxy because it is available for rapid damage assessment in buildings with permanent monitoring systems or for city-scale post-earthquake surveys. Time-variable damage state probabilities owing to aftershocks are estimated, and a building tagging scheme is proposed based on a traffic-light concept (red-orange-green) to assist in seismic crisis management during aftershock sequences.