The Courier & Advertiser (Angus and Dundee)
QUAKING SCOTLAND
Michael Alexander asks Fife-raised British Geological Survey seismologist Dr Brian Baptie why there has been a spate of Perthshire earthquakes and what trends might develop in the long-term future
T hey are among the most powerful natural disasters on Earth with the potential to cause devastating loss of human life, destruction of property and massive humanitarian disruption.
But while it’s been many millennia, if not millions of years, since what we now call Scotland last saw earthquakes on a scale of those now experienced in some other parts of the world, earthquakes on a much smaller scale do occur in and around the British Isles almost every day.
One such area known for its “earthquake swarms” is south Perthshire.
At the end of November, the British Geological Survey (BGS) recorded a 2.0 magnitude tremor which led some residents in the Blackford, Auchterarder, Aberuthven, Braco, Gleneagles, Glendevon and Greenloaning area to believe there had been an “explosion”.
The epicentre was near Gleneagles golf course with people reporting their “whole house shook” and “windows and doors rattled”.
It was the 20th time the area had been hit by an earthquake in just over two months following a 0.9 magnitude quake on November 21 and two tremors within six minutes of each other four days earlier, measuring 0.7 and 0.9 magnitude.
Another 0.7 magnitude quake was recorded on November 11.
But while seismic activity on this scale rarely causes damage and mostly passes unnoticed, from the perspective of the BGS, which measures seismic activity via 80 sensors deployed across the UK, it gives a fascinating insight into ancient fault lines and ever-changing geological pressures deep within the Earth’s crust.
“We can’t be specific about which faults are responsible for these earthquakes in Perthshire,” says Kirkcaldy-raised BGS head seismologist Dr Brian Baptie.
“But we know there are historic observations of earthquakes in Scotland that date back hundreds of years – back to the 14th Century – and there are lots and lots of accounts of earthquakes that have been felt by people.
“Similarly when we first started deploying sensors to measure earthquakes across the UK from the 1970s onwards, the first of those sensors were in and around the Midland Valley in Scotland up into Perthshire and those started to reveal lots of small earthquakes as well as these more frequent larger ones.”
Geological faults are the main reasons for earthquakes, says Dr Baptie, who first became hooked on science while watching the infamous eruption of Mount St Helens in the USA on TV in 1980.
Even though we are far from any of the world’s earthquake hotspots, the earth under our feet is still being slowly squeezed and that leads to the stress that builds up on these faults.
After a period of time the stress overcomes resistance, the rocks slide past each other and that releases energy in the form of these seismic waves, or vibrations, that travel through the Earth and make the ground shake.
Scotland’s largest recorded earthquake was in 1880 when a 5.2 magnitude quake centred on Loch Awe in Argyll was widely felt all over the country. Fortunately the epicentre was in a relatively remote area where population density is quite low.
In 1894 there was a magnitude 5 in Fort William and in 1901 there was another magnitude 5.1/5.2 earthquake in Inverness that caused quite a lot of mainly superficial damage to buildings. Chimney pots came down, plaster cracked and roofing materials were dislodged.
In August 1974, a 4.4 magnitude earthquake which had its epicentre in Kintail in the north west Highlands was part of a “swarm” of 20 seismic events that followed.
However, for an earthquake to be felt, the threshold is round about magnitude 2. Anything smaller than that is unlikely to be noticed. Yet the incredible sensitivity of BGS sensors means that today they can measure very small vibrations down to something like 1/1000th of a micron or a millionth of a millimetre.
Dr Brian Baptie obtained his PHD in Seismology from Edinburgh University in 1995.
He joined the British Geological Survey in 1996 as a member of the multi-disciplinary team monitoring the eruption of the Soufriere Hills Volcano in Montserrat, West Indies, where he was responsible for all aspects of the seismic monitoring intended to improve understanding of volcanoes and earthquakes.
While working on Montserrat he collaborated widely with colleagues both within the UK and overseas on work that has helped to gain key insights into the nature of volcanic earthquakes.
In 1999 Brian joined the Seismology and Geomagnetism Programme to work mainly on improving understanding of natural seismic activity in the UK and offshore areas.
In 2008 he became team leader of the Earthquake Seismology Team.
He has also continued to study active volcanoes, including the ongoing eruption of the Soufriere Hills and Eyjafjallajokull.
Looking back through history, some of the most devastating earthquakes ever recorded were in China, causing more than half a million casualties.
One of them was in the 1550s in an area with high concentrations of people and buildings.
More recently, the 1976 Tangshan quake resulted in more than 242,000 deaths.
“Generally, places where you get big earthquakes and places where population densities are high, like Japan, Indonesia, China, those are the places that you can get the devastating earthquakes,” he says.
“Smaller earthquakes can also cause devastation. They don’t need to be magnitude nine earthquakes – you can get 7/7.5 earthquakes that are capable of devastating cities.
“The 2004 Boxing Day earthquake and tsunami resulted in something like 200,000 deaths not just in Indonesia but across the wider area – Sri Lanka, Thailand.”
Brian says science has certainly “moved forward” in terms of predicting earthquakes worldwide.
However, scientists are still not very good at making one-off predictions.
“We may never be able to predict oneoff earthquakes just because they are quite random,” he says.
“But we are much better at making longerterm forecasts.
“Over time periods of say 50 years or 100 years, we can work out probabilities of earthquakes happening and probabilities of how strong those ground motions will be.
“That means within those time scales we can start to engineer buildings properly and take measures to prepare people so they know what to do in the event of an earthquake. The buildings should at least be resistant.
“But obviously that preparation is quite a costly process as well.
“The countries that are well prepared for earthquakes like the US or Japan – or even countries in South America like Chile – are relatively rich while much poorer countries they have much fewer resources for that kind of thing.”
While residential housing stock in Scotland is not designed with earthquakes in mind due to the risk being so low, sensitive structures like nuclear power stations and dams are constructed with earthquake engineering resistance.
But given enough geological time, is it possible Scotland could again be struck by massive earthquakes at some point in the distant future as it was millions of years ago?
“That’s possible,” says Brian. “If we think about plate tectonics and movements of the plates in those kind of time scales and where we are now, if a plate boundary was to form close to Scotland or close to the UK then sure we could start to experience many more earthquakes.
“The most likely scenario for that is what we call a subduction zone opening up on the edge of the Atlantic – the Atlantic Oceanic plate being pushed down underneath the European plate – so something like that is not impossible over those kind of time scales.
“The other interesting thing possibly is if there was to be another ice age.
“If there were to be an ice cap over the UK or over Scotland like there was round about one million years ago or so, that can change seismic activity because of loading.
“Especially if the ice cap forms and melts again, you can actually, in theory, see much higher levels of earthquake activity as a result of this isostatic rebound or glacial rebound process.”
WE MAY NEVER BE ABLE TO PREDICT ONE-OFF QUAKES