How clearly an earthquake is felt depends not only on its strength, but also on the depth of its seismic focus (hypocentre) and on the local subsoil.
Earthquakes in soft ground (e.g. in valley sediments, lake deposits) are felt more than earthquakes in rocky subsoil. The type of subsoil in the locality also affects the resulting damage: earthquake waves in sediment-filled valleys (like the Rhone Valley) are 10 times stronger than in solid bedrock and cause correspondingly greater damage. As a rule, the more solid the subsoil beneath a building is, the less damage earthquake waves can cause.
Watch the video to see how the waves in a simulated earthquake in the Rhone Valley spread and how long they remain 'trapped' in the valley floor.
In principle, near the epicentre, earthquakes with a magnitude of 2.5 or above can be felt. Only rarely do we receive earthquake notifications for events with a magnitude of just under 2. Earthquakes with magnitudes of 3 or higher are felt by large numbers of people; at magnitudes of between 4 and 5 they can be felt within a radius of up to 200 kilometres; and at magnitudes of 5 or more they can be felt up to several hundred kilometres away under some circumstances.
These increasing radii are due to the fact that the energy released by an earthquake increases by a factor of 30 per level of magnitude, making a magnitude 5 earthquake 30 times stronger than a magnitude 4 earthquake.
You can see how the energy released increases exponentially in the video.
The impact of an earthquake on the surface (i.e. on buildings, people, the environment and infrastructure) is described according to a 12-level intensity scale (see EMS-98 below).
Damage to buildings can be expected starting from an intensity of around VI, which corresponds to a magnitude of approximately 5. Destructive damage is to be expected after an earthquake with an intensity of IX or above. Minor cracks or damage caused by falling objects can even occur at lower intensities.
The table on the Federal Authorities' National Hazards Portal shows the anticipated impact of earthquakes of various sizes in Switzerland.