Ground motion simulation in Beirut from a large earthquake on the Mount Lebanon Thrust fault

Ground motion simulation is crucial for seismic risk assessment in cities with limited recorded strong ground motion data. Lebanon is located along the Dead Sea Transform fault system, which previously generated large earthquakes, but has recently experienced only low to moderate instrumental seismicity. Beirut, the capital of Lebanon, was destroyed in 551 AD due to a large magnitude earthquake (M_S7.3) offshore Lebanon that was attributed to the Mount Lebanon Thrust fault (MLT). In addition, Beirut is densely populated nowadays, and seismic design requirements were only recently introduced in Lebanon. Thus, seismic risk assessment studies for Beirut should consider large-magnitude earthquake scenarios on the MLT, e.g., similar to the 551 AD historical earthquake. The lack of strong motion records from the MLT source underscores the need for ground motion simulation. In this work, we first identify the plausible earthquake scenarios on the MLT by fitting radiocarbon-dating and uplift data at the Lebanese coast to simulated static deformations from scenarios on the MLT. Next, we develop a improved hybrid ground motion simulation method, which combines deterministic simulations at low-frequency (LF) (<0.5 Hz) and a stochastic approach at high-frequency (HF). The LF part is based on pseudo-dynamic rupture models and a recently developed one-dimensional velocity model of Lebanon. On the other hand, the HF part consists of an improved version of a near-fault site-based stochastic model that accounts for specific features of near-fault ground motions, such as directivity velocity pulses, conditioned on the LF ground motion properties. Using this model, we simulate ground motions at a grid of virtual stations in Beirut. These simulations will be used in future works for a city-scale comprehensive structural damage estimation in Beirut for the selected scenarios.