Offshore Tsunami Deposits: Evidence from Sediment Cores and Numerical
Wave Propagation of the 1601 CE Lake Lucerne Event
Abstract
The 1601 Common Era earthquake (Mw ca. 5.9) in “Unterwalden”, Central
Switzerland triggered multiple subaqueous mass movements and a subaerial
rockfall that generated tsunami waves with devastating run-up heights of
up to 4 m and several hundred meters of inundation along the coastal
lowland plain of Lake Lucerne. In the shallow Lucerne Bay at the outlet
of the perialpine lake, historical chronicles reported a seiche with an
initial amplitude of ~1–2 m and a period of 10 min that
decreased with time but persisted for several days after the event. The
impact and erosion potential of the tsunami wave on the Lucerne Bay is
assessed with sediment core analysis and numerical simulation of wave
propagation. A 60 cm thick offshore event deposit was recovered and
radiocarbon dated along a sediment-core transect. The event deposit has
a sharp basal contact with carbonate shell fragments and a normal graded
succession of siliciclastic sand to silt with high amount of
terrestrial-derived horizontally bedded wooden particles. The simulated
tsunami waves have a water-surface displacement of up to 1.5 m and bed
shear-stresses that are likely capable of remobilizing large amounts of
sediment in the Lucerne Bay area. Our study thus successfully links the
sedimentology of event deposits with physical principles of sediment
mobilization derived from numerical wave modeling, providing a tool to
improve the identification and interpretation of potential tsunami
deposits.