Evaluation of tsunami risk from regional earthquakes at Pisco, Peru

We evaluate tsunami risk for the port city of Pisco, Peru, where major liquefied natural gas facilities are planned. We use a compilation of instrumental and historical seismicity data to quantify the sources of six earthquakes that generated tsunamis resulting in minor inundation (1974) to catastrophic destruction (1687, 1746, 1868) in Pisco. For each of these case scenarios, the seismic models are validated through hydrodynamic simulations using the MOST code, which compute both flow depth on virtual offshore gauges located in Pisco harbor and the distribution of runup in the port and along the nearby beach. Space-time histories of major earthquakes along central and southern Peru are used to estimate recurrence times of tsunamigenic earthquakes. We conclude that Pisco can expect a metric tsunami, capable of inflicting substantial damage every ∼53 years, and a dekametric tsunami resulting in catastrophic destruction of infrastructures every ∼140 years. The last such event occurred 138 years ago. An important result of our study is that total destruction of the city of Pisco during the famous 1868 Arica tsunami requires an earthquake rupture straddling the Nazca Ridge, which thus constitutes at best an imperfect "barrier" for the propagation of rupture during megathrust events. This gives a truly gigantic size to the 1868 Arica earthquake, with a probable seismic moment reaching 10³⁰ dyne cm.