Extreme value analysis of design events

Design events are used in avalanche engineering applications like hazard zone mapping, di- mensioning of protection measures or the optimization and calibration of computational simulation software. A design event is defined by its return period that is related to a certain magnitude. It is often determined by the run out length of single historically documented avalanche events accompanied with subjective period estimates. Avalanche paths with detailed, continuous records are rare and therefore statistical analysis can hardly be realized for most avalanche paths. In this work we perform design event estimates for the Arzler-Alm avalanche situated above the Tyrolean capital Innsbruck, Austria. Avalanches in urban areas raise special attention, due to of their constant threat to life. Consequently several historical avalanche records articles exist since the year 1859. Refinement of protection measures around the avalanche path led to continuous observations of the avalanche activity be- tween 1945 and 1970. Due to the number of good quality observations extreme value statistics is an adequate method to combine the information of frequent and historical sources. Based on the methods of extreme value theory, employing observations of frequent avalanche run out distances, we discuss an approach to improve the estimation of (1) return periods of historical events and (2) the design event intensities. For avalanches of high return periods the analysis shows that extreme run outs can be limited to a specified range, while return period estimates are subject to high uncertainties.