Strong earthquakes on the French-Italian Mediterranean Riviera

We present a joint analysis of all available seismological, geodetic and geological data to assess seismic hazard along the vulnerable French-Italian Riviera. This is achieved by discussing the most likely scenario and quantifying recurrence times for strong earthquakes. The most destructive earthquake known in the area (1887, Mw ~ 6.8) occurred offshore on the Ligurian Fault. This event is typical of strong but sporadic earthquakes that can provide valuable insights into the behavior of low-slip-rate faults. Given the uncertainties on each type of data, the results of the different approaches indicate a wide range of recurrence times for such an earthquake, from 607 to 15,969 yr. Considering the most probable values refines this range to 2353-9484 yr. Variations in seismicity rate associated with changes in geodynamic and environmental conditions are also discussed. Since the 1887 earthquake only ruptured the central part of the Ligurian Fault, the largest future hazard is posed by the adjacent fault segments, which could generate an event of similar magnitude. A joint analysis of seismological, geodetic and geological data constrains the recurrence time of large, potentially tsunamigenic and destructive earthquakes on the Ligurian Fault on the Mediterranean French-Italian border to between 2,353 and 9,484 years