The 1908 Messina Tsunami: New Understanding of Coastal Impact Through Numerical Modeling of Dual Coseismic-Landslide Sources

In the morning of December 28, 1908, a Mw 7.1 earthquake struck southern Italy along the Messina Straits, killing 60,000 people. Within a few minutes, a tsunami struck the coasts of Sicily and Calabria causing further loss of life and property damage. Immediately following the event, measurements and survivor accounts of the tsunami were acquired, providing a valuable resource for future research. Attempts to reproduce the tsunami from coseismic mechanisms always underpredicted recorded and observed tsunami inundation and runups. Recently, a submarine landslide, triggered by the earthquake, was proposed as an alternative tsunami mechanism. Using backward wave ray tracing, based on reported tsunami arrival times, the landslide was located north east of Mount Etna. Numerical tsunami simulations based on various, often assumed, landslide volumes together with the earthquake, resulted in improved agreement with observed runups at some locations, but not all. Agreement on the precise mechanism of the tsunami, earthquake or landslide, has yet to be reached. Based on new dual source, earthquake and submarine landslide scenarios, using higher-resolution bathymetric and topographic data, we present new tsunami simulations. New ray tracing, based on the tsunami arrival times, including a realistic time delay, provides a revised location for the landslide; a location confirmed by re-interpretation of the bathymetric data. Our analyses identify an area on the NE flank of Mt. Etna where there is evidence for a ~2 km3 underwater slump. We first simulate tsunami impact with the Boussinesq model FUNWAVE, for four different coseismic sources, which confirms that these all cause low elevation runups, which do not reproduce recorded observations. We then include the slump in dual source simulations, using the nonhydrostatic model NHWAVE to simulate tsunami generation (in a 120 m resolution grid). We perform tsunami propagation simulations in 30 m resolution nested coastal grids using FUNWAVE. The result is an improved agreement with the recorded runups directly onshore of the slump. Elsewhere, runups are still underestimated. Based on our new research we conjecture that there are additional submarine mass failures farther north of our slump. Simulations of these are ongoing, results of which will be presented at the conference.