Earthquakes are caused by a sudden release of stress along faults in the earth's crust. The continuous motion of tectonic plates causes a steady build-up of pressure in the rock strata on both sides of a fault until the stress is sufficiently great that it is released in a sudden, jerky movement. The resulting waves of seismic energy propagate through the ground and over its surface, causing the shaking we perceive as earthquakes. The magnitude is a measure of earthquake size in terms of the energy released at the source. It is calculated from the amplitude of the instrumentally measured ground motion (seismograms). Magnitude is a logarithmic value, and an increase of one magnitude signifies a roughly 30-fold increase in energy.

On average, the Swiss Seismological Service (SED) registers two earthquakes per day in Switzerland and its neighboring countries, making a total of between 500 and 800 earthquakes a year. Approximately 10 to 15 of these events are strong enough to be felt by the population (i.e. have a magnitude of approximately 2.5 or above). Earthquakes with a magnitude of at least 5 occur every 8 to 15 years. Larger earthquakes, with a magnitude of 6 or more, occur only every 50 to 150 years. Though rare, they can occur anywhere and at any time in Switzerland. The strongest historically documented earthquake in Switzerland, with a magnitude of approximately 6.6, occurred in Basel in 1356. Such events should be expected to happen roughly once every 1,500 years.

As a result of plate collision, strong earthquakes have occurred in the Alps and their surroundings time and time again in the past. Information from historical sources and modern earthquake catalogs show that there were at least 12 earthquakes with a magnitude of 6 or more in the past thousand years. The last major earthquake took place in 1976 in northern Italy (M6.5) followed by two aftershocks with magnitudes greater than 6 within a few months. This Friuli quake claimed 989 lives and injured 2,400 people; about 45,000 were left homeless as a result. Although the extent of damage for historical events can sometimes be difficult to estimate, it is likely that at least three of the quakes caused more than 10,000 deaths.