The primary goal of permanent stations is to monitor seismicity, the activity of earthquakes with time. Therefore the longer we measure, the more we know about the behaviour of the underground.
Two kinds of sensors are used at seismic stations:
- Broadband sensors that are designed to detect even the smallest ground vibrations from very small nearby earthquakes (magnitude M<1) as well as regional and teleseismic (distant) events. Earthquakes of Magnitude 5 and more can even be recorded from the other side of the globe.
- Strong motion sensors (“accelerometers”) record strong ground motion from nearby large earthquakes.
In Switzerland, the SED operates about 45 broadband stations located at remote and quiet sites with little background noise. The approximately 60 strong motion stations are mostly placed within cities in order to characterise the motions in the areas of high risk from rare large earthquakes. More on this as well as on the SED’s permanent networks can be read here.
The locations of the permanent stations are chosen from a scientific point of view. It is not only important to place a station close to the expected region of seismicity; it is at least as important to construct a network of stations that covers well the sources of seismicity, from all directions. Earthquakes can only be accurately located if they are recorded by many stations, some close to the epicentre, with good distribution in all directions.
Watch a short film showing the installation of a seismic station at the Mont Terri Rock Laboratory by the Swiss Seismological Service in early 2014: