Seismic risk scenarios for Beirut, Lebanon

Lebanon is an earthquake-prone country along the Levant Fault System, with three branches within 35 km of Beirut. Thus, this study focused on establishing seismic risk scenarios for Beirut, Lebanon, through the Deterministic Seismic Hazard Analysis (DSHA) approach considering lithological site effects. Three seismic scenarios were studied on the Mount Lebanon Thrust fault, Roum Fault, and Yammouneh Fault. Seismic hazard determination was done through the estimation of the Peak Ground Acceleration (PGA) using the Ground Motion Models (GMM) of Akkar et al. (2014), Chiou and Youngs (2014), and Kotha et al. (2020) and then converting these values to macroseismic intensities. In all models and scenarios, lower PGA and intensities were found, located along the Achrafieh and Ras Beyrouth hills. PGA of up to 1.50 g was obtained for Mount Lebanon Thrust fault, resulting in an intensity of up to XI. Meanwhile, both Roum and Yammouneh Faults generated a maximum PGA of 0.25 g and a maximum intensity of VIII. Mean damage grade and damage grade distribution prediction in Beirut were determined based on the vulnerability indices of the buildings that are based on the RISK-UE methodology. Beirut consists mainly of masonry and reinforced concrete buildings with a maximum plausible vulnerability index of 0.953 and 0.800, respectively. Beirut was found to have the highest mean damage grade of 4.53 due to the seismic scenario of the Mount Lebanon Thrust fault. Earthquakes on both Roum and Yammouneh Faults generated similar mean damage grades at 1.71. For the damage grade distribution, 30 – 40% of the buildings in Beirut were expected to experience moderate to very heavy damage. However, the impact of site effect on the damage grade distribution in Beirut was not observed, suggesting that lithologic site effects play no significant role in damage grade prediction in the Beirut context. The results of this study can serve as a basis for improving the building code of Beirut and Lebanese seismic design, to strengthen and regulate earthquake safety and conditions. Potential improvements in policies related to these results are essential economically and help in preserving cultural heritage, as historical buildings are among the most vulnerable structures to earthquakes.