Did you feel that?
Dr Georgios S. Papavasileiou, Lecturer in Civil and Construction blogs about the latest Earthquake that shook the Black Country.
The term 'earthquake' refers to the sudden shaking of the surface of the earth. Earthquakes occur naturally around the world - this is because the Earth’s crust while solid it is not uniform. It comprises a number of plates which are in contact with each other, but also tend to move in different directions and so they interact with each other. This contact prevents the relative movement and so energy is accumulated in the contact surfaces referred to as faults. When the amount of accumulated energy surpasses the capacity of the fault, it will result in local failure which will allow the sudden relative movement of the two plates, releasing energy and creating the seismic waves. The plates will stabilise again at a different position where the process will repeat. In principle, contact surfaces between the largest plates, also referred to as ‘major plates’ would have the ability to accumulate significant amounts of energy and so when released this will result in strong earthquakes. Of course, there are faults that would typically produce weaker earthquakes as well.
The UK mainland is not very close to one of the faults that can produce very strong earthquakes, and therefore the recorded seismic activity comprises low to medium intensity seismic events with the latter being quite rare.
Earthquakes can also take place due to human activity. This is what we refer to as ‘induced seismicity.’ Such activities which would affect big areas could be related to natural gas extraction through hydraulic fracturing, mining operations, waste disposal wells, groundwater extraction and geothermal energy harvesting. In the UK such events would typically take place more often than natural earthquakes and, while there have been strong earthquakes related to human activity worldwide, it is predominantly responsible for low-intensity earthquakes.
According to the British Geological Survey, the earthquake that took place in the West Midlands last night was of a magnitude of 2.8, which would categorise it as a ‘minor’ earthquake.
So, why did many people feel the earthquake? The reason is that, as significant seismic events are very rare in the UK, we do not design our typical residential buildings against earthquake. This should not be alarming, though, as our structures, provided that the construction quality is good, have an inherent ability to withstand minor seismic events even without developing any damage at all. However, minor earthquakes could on some occasions result in damage of brittle non-structural components or cause objects to fall and potentially cause injury (e.g. unsecured objects, or overloaded bookcases). Nevertheless, in the UK we have the codes to design buildings against earthquake, while for buildings of increased significance this is a hazard considered in their design.
Overall, the event last night is not a frequent occurrence in the mainland of the UK and certainly not a reason of concern. It is a reminder though of the need for good quality in construction and our responsibility to ensure that there are no unsecured objects in our homes that could fall and cause injury.
Dr Georgios S. Papavasileiou is a Lecturer in Civil and Construction Engineering at the University of Wolverhampton. His expertise is in structural engineering with a focus on multi-hazard design of structures, sustainable structural design and retrofit, and structural optimisation. His publication record comprises numerous works in international peer-reviewed journals, most of which are in the field of earthquake engineering.
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