[S08-2] Paleoseismology and paleotsunami studies: Their potential and limitation II

[S08-2-01] Large earthquakes in historical and pre-historical times in Switzerland: An overview of earthquake induced effects

^○Donat Faeh¹, Gabriela Gassner-Stamm¹, Michael Strasser², Remo Grolimund¹, Stephanie Wirth³, Katrina Kremer¹ (1.Swiss Seismological Service, ETH Zurich, 2.Geological Institute, University of Innsbruck, 3.Centre for Hydrogeology and Geothermics, University de Neuchatel)

invited

During the last years, many studies have investigated pre-historical and historical earthquakes from traces left in sediments and the environment. The goal of this study is to gather and systematize available data potentially relevant for understanding seismic activity in Switzerland before the start of reliable historical records and to analyze it for the first time all together. The Earthquake Catalogue of Switzerland (ECOS-09) covers the period from 250 to 2009 AD and is only scarcely populated with events before 1100 AD. The new database extend back 0.5 Ma years, but is more rich in information for the time since 20'000 BP. Primary data for this new data collection come from recent paleoseismic studies and from studies from other disciplines (Sedimentology, archaeology, speleology, geomorphology and historical research) that focused on other goals, but include observations of potential relevance for understanding past strong ground shaking. Considering the combined data set, we identify 23 periods with an increased number of possible earthquake-induced effects. While all these effects could belong to various small earthquakes, or have a totally different, earthquake-independent origin, one admissible hypothesis we want to follow up in this study is also, to cluster these effects within time periods of increased number of observations, and to assign them to single earthquakes. For events after 1600 AD, highly reliable historical records are available, and earthquake induced effects can be assigned to known historical earthquakes. For the older period, eight events can be identified with paleoseismological evidence distributed over a wider area, possibly indicating a strong earthquake or a period of overall increased seismicity throughout Switzerland. The most prominent event occurred in the period 1900-2270 cal years BP. If assumed to be one single earthquake, it would be the strongest earthquake in the last 5'000 years in Switzerland.