Investigating tsunami hazard in Switzerland

Tsunamis are not limited to the ocean. On rare occasions, large flood waves also occur in lakes, including those in Switzerland. According to historical reports and investigations of lake sediments, a wave up to 8 m high swept across Lake Lucerne in 1601, resulting in widespread flooding. It was triggered by a magnitude 5.9 earthquake in the canton of Nidwalden, whose tremors caused several underwater landslides in Lake Lucerne and a rock avalanche on the Bürgenstock, which in turn triggered the tsunami. Tsunamis have also been recorded on Lake Geneva, Lake Brienz and Lake Lauerz .

A research project recently approved by the Swiss National Science Foundation aims to determine the risks posed by these rare events, what it takes to trigger lake tsunamis, how often they have occurred in the past, and the impact they create. As part of the project, scientists from ETH Zurich, the University of Bern and the University of Bremen's Centre for Marine Environmental Sciences (Marum) are planning to install nine ocean-bottom seismometers on the bed of Lake Lucerne. They will be the core equipment used to take seismic and geotechnical measurements of the lake sediments. Applications were also submitted to the Cantons of Lucerne, Nidwalden and Schwyz, but Lake Lucerne was chosen because of its location in a region of comparatively high seismic hazard and also because a lot is known about the lake bottom from previous research projects.

The plan is to place the measuring devices at various locations in the lake for a period of 22 months. The seismic data collected, combined with other measurement results, will be used to characterise the internal structure of slope instabilities, to better understand their slide mechanics and to model the generation and propagation of tsunami waves. Such a comprehensive investigation of hazard processes beneath the water surface is the first of its kind in Switzerland and its findings will help to improve the understanding of such processes around the world. The total cost of the project is CHF 2 million, much of which will be spent on the complex process of collecting the measurements.