As a rule, it takes measurement data from several seismic stations to ascertain exactly when and where an earthquake occurred. For this reason, more than 100 such stations spread across the country, set up and run by the Swiss Seismological Service (SED), monitor earthquake activity around the clock in Switzerland and its neighbours. The data they record are gathered, almost in real time, by the SED's data centre in Zurich and automatically analysed. As soon as at least six stations register signals indicating potential seismic waves, the system tries to pinpoint where the earthquake originated (see the question "What's a hypocentre and what's an epicentre?") and when it occurred, based on the times at which the signals were received.

The key here is that stations located close to an earthquake's place of origin register the seismic waves earlier than more distant stations. Furthermore, earthquakes cause different kinds of waves, which spread through the ground and across the surface of the planet at different spreads (see the question "What are P, S, Love and Rayleigh waves?"). Based on these timing differences and a velocity model specially devised for Switzerland (seismic waves pass faster through dense Alpine rock and deep layers of the Swiss plateau than through the plateau's sedimentary basin), an earthquake's time of occurrence and place of origin can be very precisely determined. Moreover, the SED’s 24-hour on-call service manually analyses and recalculates the location of every earthquake, taking account of other properties of the various types of earthquake waves as well.