Danger levels earthquakes
Earthquakes are caused by a sudden release of stress along faults in the crust. Due to continuous motion of tectonic plates, stress builds in the rock on both sides of a fault. When the stress exceeds the strength of the rock, it is released in a sudden, jerky movement. The released seismic energy propagates as waves through the earth and along its surface, and these waves cause the shaking that we feel.
The levels of danger refer to the intensity of an earthquake in a specific warning area. The intensity is a measure of the effects of an earthquake. Using a 12-point scale, it describes the consequences of an earthquake for people and buildings in a particular place. An earthquake has one value for magnitude (energy released) and usually several values for intensity. The greatest intensity is usually recorded close to where the earthquake takes place (epicenter) and decreases with distance from the epicenter.
For each warning area, the Swiss Seismological Service at ETH Zurich estimates the intensity in the center of each region and assigns a particular danger level based on this (see table below).
The danger levels described do not represent the actual seismic hazard. In principle, major damaging earthquakes may occur in Switzerland at any time and anywhere. If no danger level is displayed, this simply means that no earthquake notifications for an earthquake with a magnitude of 2.5 or greater are currently in place for the selected warning area. By contrast, the seismic hazard describes how often and with what magnitude vibrations triggered by earthquakes can be expected within a certain time in a certain location.
Danger level 1 (little to no danger)
Effects
Noticed by few people. No likelihood of damage to buildings.
These effects correspond to an intensity of III*.
This level of intensity may be reached with earthquakes with a magnitude of around 2.5 or greater.°
What to do
There is no specific advice on what to do in the event of a danger level 1 earthquake. Earthquakes capable of causing damage can occur anywhere and at any time in Switzerland. For further information see What to do during an earthquake.
Description Measurement and forecast values
- Potentially felt.
- Intensity III
Danger level 2 (moderate danger)
Effects
Felt in scattered locations outdoors and noticed by many people in buildings. Generally no likelihood of damage to buildings.
These effects correspond to an intensity of IV*. This level of intensity may be reached with earthquakes with a magnitude of around 3.5 or greater.
What to do
Take cover, be ready for further and partly strong earthquakes. For further information see What to do during an earthquake.
Description Measurement and forecast values
- Felt across a wide area, no likelihood of damage to buildings.
- Intensity IV
Danger level 3 (significant danger)
Effects
Likelihood of damage to buildings such as cracks in plaster. High likelihood of larger cracks in walls and interior wall collapse in less stable buildings. Damage is likely to be caused by falling objects in buildings. The earthquake is felt across a wide area, people are alarmed.
These effects correspond to an intensity of V or VI*. These levels of intensity may be reached with earthquakes with a magnitude of around 4 or greater.
What to do
Take cover, be ready for further and partly strong earthquakes. For further information see What to do during an earthquake.
Description Measurement and forecast values
- Felt across a wide area, likelihood of minor damage to buildings.
- Intensity V or VI
Danger level 4 (high danger)
Effects
Likelihood of severe damage to buildings. Less stable structures may have collapsed. Damage was highly likely to be caused by falling objects in buildings. The earthquake was felt strongly, people were alarmed and lost their balance.
These effects correspond to an intensity of VII*. This level of intensity may be reached with earthquakes with a magnitude of around 4.7 or greater.
What to do
Take cover, be ready for further and partly strong earthquakes. For further information see What to do during an earthquake.
Description Measurement and forecast values
- Felt strongly, likelihood of severe damage to buildings.
- Intensity VII
Danger level 5 (very high danger)
Effects
High likelihood of severe damage to buildings, even to very stable structures. Buildings may have collapsed. The earthquake was felt very strongly, people were alarmed and lost their balance.
These effects correspond to an intensity of VIII or greater*. This level of intensity may be reached with earthquakes with a magnitude of around 5.4 or greater.
What to do
Take cover, be ready for further and partly strong earthquakes. For further information see What to do during an earthquake.
Description Measurement and forecast values
- Felt strongly, high likelihood of widespread and severe damage to buildings.
- Intensity VIII or greater
Explanations:
* On the European Macroseismic Scale (EMS-98)
° Information about earthquakes of a magnitude of less than 2.5 is not publicized on naturgefahren.ch. This information can be found at http://www.seismo.ethz.ch.