It is devoted to the detailed monitoring of the earthquake activity in northern and central Switzerland. The main objective of this study is to provide information about the locations of active deformation and the state of stress in the Earth's crust and to relate these to the geological features visible at the surface. Here we review the seismic activity and earthquake focal mechanisms of the last 10 years and subsequently derive a comprehensive picture of the deformation and stress in the Earth's crust of northern Switzerland, based on all data available up to the end of 1999. Concerning the seismotectonics of central Switzerland, this publication constitutes the first publicly available report. A remarkable feature visible on recent epicenter maps is the concentration of seismicity in clusters of closely spaced epicenters, which in most cases correspond to individual earthquake sequences of limited duration.
Focal depths range from the near-surface sediments down to the base of the crust.
The strongest earthquake of the past 10 years, attained a magnitude of 4.0 and occurred in 1996 at a depth of 30 km near Kirchberg in the Untertoggenburg. The others either are normal faulting mechanisms or cannot be associated uniquely to a distinct faulting type. The overall deformation and stress field of the Earth's crust in northern Switzerland is characterized by subhorizontal ENE-WSW oriented axes of maximum extension and of minimum stress. About 10 earthquakes with epicentral intensity of at least VII are known to have occurred in central Switzerland since the 14th century. Half of these took place between 1774 - 1777 around Altdorf and Sarnen.