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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.
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