The number of earthquakes recorded depends not only on seismic activity, but also on the density and distribution of monitoring stations. Regions where many seismic stations have been set up, such as the canton of Valais or Eastern Switzerland, record comparatively higher numbers of quakes, because even very small events can be recorded and analysed. Moreover, in principle there is more small-scale than large-scale seismic activity. For example, more than 700 of the 1,230 earthquakes registered by the SED in 2017 had a magnitude of less than 1.0. In recent years, the number of recorded microquakes has greatly increased, due to the steady expansion of the measuring network and improved analytic methods. It is important to record such events because this allows geoscientists to learn more about the structure of the subsurface and to draw conclusions about the seismic hazard.
Compared to other European countries, Switzerland has a moderate seismic hazard, but displays regional differences, the canton of Valais having the highest hazard, followed by Basel, Grisons, the St. Gallen Rhine Valley, Central Switzerland and then the rest of the country. Every region of Switzerland is exposed to some degree of seismic hazard.
Most of the earthquakes occurring in Switzerland are caused by collisions between the European and the African lithospheric plates.