Historical seismicity in Central Switzerland

An overview of seismic activity in Central Switzerland is presented. As earthquake activity has been very low for the time period of modern instrumental observation, we focus on the largest known earthquakes in the historical past (September 18, 1601, September 10, 1774, January 23, 1775, and the swarms of 1777 and 1964). The epicenters of these events indicate a concentration of activity around Altdorf (1774, 1775) and Sarnen (1601, 1777, 1964), whereas recent instrumentally observed microearthquakes are distributed more evenly over the whole area. Moreover, earthquake activity was extraordinarily low since the beginning of modern instrumental observations. The irregular episodes of strong earthquakes, both in space and time, characterize the seismicity of Central Switzerland. The results of the study make it evident that earthquake activity is not necessarily stationary. As earthquake recurrence intervals are important factors in seismic hazard assessment, well-documented information on historical earthquakes are particularly important.