What do we see on the risk map?
Areas where there are possible earthquake risks are indicated on the risk map by a line (fault lines) or surface (cavern or Mercalli zone). The possible effects of an earthquake are shown on the risk map according to the Mercalli intensity scale.
The possible effects of an earthquake are shown on the risk map according to the Mercalli intensity scale. The scale runs from I (instrumental) to XII (catastrophic). The Richter scale is the most common measure of an earthquake’s force. However, the Richter scale only measures the underground force of the quake at the source, which may be very deep and far away (‘the epicentre was…’). The Mercalli scale measures the earthquake at a specific location.
Earthquakes are often linked to fault lines in the subsurface. The areas on either side of fault lines may slowly start to shift. Sometimes they do so in jolts, causing an earthquake. Major fault lines are indicated on the map with a line symbol. The same symbol is used to indicate where the land elevation may suddenly drop owing to drilling or mining activities (natural gas, salt).
A cavern is an underground space created by the extraction of minerals. An example is salt mining. Gas drilling does not lead to caverns. Caverns are shown on the risk map only if they are capable of causing noticeable earthquakes.
What can you do yourself?
The website of the Royal Netherlands Meteorological Institute [KNMI] contains more information about aardbevingen in Nederland [earthquakes in the Netherlands].
What is the risk?
In the Netherlands, earthquakes could reach an intensity of between V and VIII on the Mercalli scale:
- V. quite strong: felt by nearly everyone, suspended objects sway, clocks stop;
- VI. strong: many frightened, objects in home overturned, trees move, poorly constructed houses are damaged;
- VII. very strong: many buildings damaged, chimneys broken, waves in ponds, church bells sound;
- VIII. destructive: general damage to buildings, poorly built structures partially destroyed.