Almost all earthquakes occur in the outer layer of our planet, i.e. in the Earth's crust. In the foothills of northern Switzerland the crust is roughly 30 kilometres thick, whereas in the Alps it is up to 50 kilometres thick. Beneath it lies the Earth's mantle. The transition between the crust and the mantle is referred to as the Moho. In the northern foothills of Switzerland, earthquakes occur right the way down to the Moho, whereas in the Alps seismic activity is limited to roughly the upper 15 to 20 kilometres of the Earth's crust.
In Switzerland, we talk of a shallow earthquake when the hypocentre lies less than 10 kilometres beneath the surface. As a rule, such near-surface earthquakes tend to be felt by people and cause more damage than deeper quakes.
