Implementation of an interconnected fault system in probabilistic seismic hazard assessment (PSHA): the Levant fault system

Abstract

The Levant fault system (LFS), a 1200 km long left-lateral strike-slip fault connecting the Red Sea to the East Anatolian fault, is a major source of seismic hazard in the Middle East. In this study, we focus on improving regional probabilistic seismic hazard assessment (PSHA) models by considering the interconnected nature of the LFS, which challenges the traditional approach of treating faults as isolated segments. We analyze the segmentation of the fault system and identify 43 sections with lengths varying from 5 to 39 km along the main and secondary strands. Applying the SHERIFS (Seismic Hazard and Earthquake Rate In Fault Systems) algorithm, we develop an interconnected fault model that allows for complex ruptures, making assumptions about which sections can break together. At first, using a maximum magnitude of 7.5 for the system and considering that ruptures cannot pass major discontinuities, we compare the classical and interconnected fault models through the seismic rates and associated hazard results. We show that the interconnected fault model leads on average to increased hazard along the branch faults and to lower hazard along the main strand, with respect to the classical implementation. Next, we show that in order for the maximum-magnitude earthquake to be more realistic (∼ 7.9), the connectivity of the LFS fault system must be fully released. At a 475-year return period, hazard levels obtained at the peak ground acceleration (PGA) are above 0.3 g for all sites within ∼ 20 km of faults, with peak values around 0.5 g along specific sections. At 0.2 s spectral acceleration, hazard values exceed 0.8 g along all fault segments. This study highlights the importance of incorporating complex fault interactions into seismic hazard models.