The British Dam Society
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About Dams

Back to safetySafety - Earthquakes

Every year, between 200 and 300 earthquakes are detected in Britain. The majority of them are very small, but about every eight years at least a Magnitude 5 earthquake occurs. It is thought that a Magnitude 6 earthquake is about the biggest that could ever occur in Britain, but the chance of that happening is very small. A Magnitude 6 earthquake can damage structures that are poorly constructed or that have not been designed to resist earthquakes.

The consequences of a dam failing during an earthquake are very serious, because the water released from the reservoir could cause severe flooding downstream. For this reason, new and existing dams in Britain are checked for the effects of earthquakes.

There are a few dams in Britain which are believed to have been affected by earthquakes. The most significant case was in 1957 when Blackbrook Dam, in Leicestershire, was affected by a Magnitude 5.3 earthquake. The tremors caused heavy coping stones to shift and cracks appeared in the faces of this gravity dam constructed from concrete and masonry.

Damaged bridge to outlet tower

Damaged bridge to outlet tower

Los Angeles Dam

Los Angeles Dam

 

These pictures show the Los Angeles Dam and outlet tower, in California, in the United States. During the Magnitude 6.8 Northridge earthquake of 1994, the bridge to the tower was damaged when the central section was dislodged from its supports and thrown sideways.

Find out more about earthquakes in Britain from the British Geological Survey