The present work aims at establishing an earthquake catalog for seismic hazard assessment in Lebanon. This catalog includes two different parts: historical earthquakes and instrumental earthquakes. The first part of the article describes the work done on the period 31 B.C.E. to the end of the nineteenth century. Numerous studies published in the last 30 yr, devoted to preinstrumental earthquakes in Lebanon, had not been included in any parametric earthquake catalog. A thorough and critical review of these studies was devised to check their respective interpretations of available earthquake records in terms of seismic parameters (date, location, and size) and to select for each earthquake the most reliable interpretation. The second part provides the details on the selection of instrumental solutions for the period 1900–2015 and for magnitudes≥4. From global instrumental earthquake catalogs, we build a unified earthquake catalog for Lebanon and bordering regions. A selection scheme is applied for the choice of the best location and the best magnitude among solutions available. The number of events in the catalog is relatively small, and all earthquakes can be checked one by one. The earthquake catalog is homogenized in moment magnitude. For 89% of the events, an Mw proxy was calculated from the original magnitude, applying conversion equations. The merging of the historical and instrumental periods highlights a specificity of this zone: the instrumental seismicity (1900–2015) corresponds to a relatively quiet period for Lebanon. The historical part, covering 2000 yr, includes similar periods of quiescence, as well as much more active periods with destructive earthquakes.

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The present work develops a comprehensive probabilistic seismic hazard study for Lebanon, a country prone to a high seismic hazard since it is located along the Levant fault system. The historical seismicity has documented devastating earthquakes which have struck this area. Contrarily, the instrumental period is typical of a low-tomoderate seismicity region. The source model built is made of a smoothed seismicity earthquake forecast based on the Lebanese instrumental catalog, combined with a fault model including major and best-characterized faults in the area. Earthquake frequencies on faults are inferred from geological as well as geodetic slip rates.Uncertainties at every step are tracked and a sensitivity study is led to identify which parameters and decisions most influence hazard estimates. The results demonstrate that the choice of the recurrence model, exponential or characteristic, impacts the most the hazard, followed by the uncertainty on the slip rate, on the maximum magnitude that may break faults, and on the minimum magnitude applied to faults. At return periods larger than or equal to 475 years, the hazard in Lebanon is fully controlled by the sources on faults, and the off-fault model has a negligible contribution. We establish a source model logic tree populated with the key parameters, and combine this logic tree with three ground-motion models (GMMs) potentially adapted to the Levant region. A specific study is led in Beirut, located on the hanging-wall of the Mount Lebanon fault to understand where the contributions come from in terms of magnitudes, distances and sources. Running hazard calculations based on the logic tree, distributions of hazard estimates are obtained for selected sites, as well as seismic hazard maps at the scale of the country. Considering the PGA at 475 years of return period, mean hazard values found are larger than 0.3g for sites within a distance of 20 to 30km from the main strand of the Levant Fault, as well as in the coastal region in-between Saida and Tripoli (≥ 0.4g considering the 84 th percentile). The study provides detailed information on the hazard levels to expect in Lebanon, with the associated uncertainties, constituting a solid basis that may help taking decisions in the perspective of future updates of the Lebanese building code.

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