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.