Fife geologist explains the “earthquake swarms” that shake Perthshire towns and villages

Michael Alexander the head of the British Geological Survey who grew up in Fife asks Dr Brian Baptie about why a wave of earthquakes has occurred in Perthshire in recent months and what trends may develop in the future.

It is among the most powerful natural disasters on Earth with the potential to cause devastating loss of human life, destruction of property and massive human disruption.

But even though thousands of years if not millions of years have passed, since what we now call Scotland the last earthquakes on the scale of those we are seeing now in some other parts of the world, earthquakes on a much smaller scale occur in and around the British Isles almost every day.

One such area, known as “earthquake swarms”, is South Perthshire.

At the end of November, the British Geological Survey (BGS) recorded a magnitude 2.0 tremor that caused some residents in Blackford, Ochterarder, Aberothven, Bracko, Gleneagles, Glendefon and Greenling to believe there was an “explosion”.

The epicenter was near the Gleneagles golf course where people reported that “their whole house shook,” “windows and doors shook” and that “looked like an explosion”.

It was the 20th time the region had experienced an earthquake in just over two months after a 0.9-magnitude earthquake on November 21 and rocked within six minutes of each other four days earlier, with a magnitude of 0.7 and 0.9.

Another earthquake of magnitude 0.7 was recorded on November 11th.

But while seismic activity at this scale rarely causes damage and often goes unnoticed, from the perspective of BGS measuring seismic activity across 80 sensors spread across the UK, it gives a great look at ancient fault lines and changing geological pressures. Constantly deep in the earth’s crust.

Historical notes

“We cannot be specific about the faults responsible for these earthquakes in Perthshire,” says Dr Brian Baptie, a chief seismologist at BGS, who grew up in Kirkcaldy.

“But we do know that there are historical observations of earthquakes in Scotland going back hundreds of years – dating back to the fourteenth century – and there are many, many accounts of earthquakes that people have felt.

Likewise, when we first started deploying seismograph sensors across the UK from the 1970s onwards, the first of those sensors were in and around the Midland Valley in and around Scotland up to Perthshire and those sensors began to detect a lot of small earthquakes in addition to these in shape. Greater frequent. “

© Submitted by BGS Dr. Brian Baptie, Head of the Seismology Division, British Geological Survey, photographed by the eruption of Mount St. Helens in 1980

Dr. Baptist, who first became addicted to science while watching the eruption of the famous Mount St. Helens volcano in the United States on television in 1980, says that geological faults are the main causes of earthquakes.

Even though we are far from any of the world’s earthquake hotspots, the ground beneath our feet is still slowly being compressed and this leads to stress that builds up on these faults.

After a period of time, the stress overcomes the resistance to faults.

The side of the rocks slide together, which releases energy in the form of these seismic waves, or vibrations, that travel across the ground and make the earth vibrate.

What is the largest earthquake recorded in Scotland?

The largest earthquake ever recorded in Scotland was in 1880 when a 5.2 magnitude earthquake in Loch Argyle was felt on a large scale across Scotland.

Fortunately, the epicenter was in a relatively remote area with very low population density.

1894 – there was a 5 on the Richter scale at Fort William and in 1901 there was another 5.1 / 5.2 earthquake in Inverness that caused a lot of surface damage to buildings. Chimney pots fell, plaster cracked, and roofing material was thrown out.

In August 1974, an earthquake measuring 4.4 on the Richter scale with its epicenter at Kintail in the Northwest Highlands was part of a “swarm” of 20 seismic events that followed.

© Provided by the BGS British Geological Survey

However, in order to feel an earthquake, the threshold is close to degree II.

It’s unlikely to notice anything smaller than this, but the amazing sensitivity of BGS sensors means that today they can measure very small vibrations down to roughly 1/1000 of a micron or a million of a millimeter.

Seismic profession

Dr. Baptist obtained his PhD. He received his Ph.D. in seismology from the University of Edinburgh in 1995, after studying the behavior of seismic waves in anisotropic waveforms and using them in determining fractured layers.

He joined the British Geological Survey in 1996 as a member of the multidisciplinary team monitoring the eruption of Soufriere Hills volcano in Montserrat, West Indies, where he was responsible for all aspects of seismic monitoring, from data acquisition to volcano interpretation. Pay attention to local radio interviews, aimed at improving understanding of volcanoes and earthquakes.

While working in Montserrat, he collaborated extensively with colleagues inside and outside the UK on work that helped gain basic insights into the nature of volcanic earthquakes.

In 1999, Brian joined the Seismology and Geomagnetism Program to work primarily to improve understanding of natural seismic activity in the UK and marine areas.

In 2008 he became the Earthquake Team Leader, the Earthquake Team.

He also continued to study active volcanoes, including the ongoing eruption of the Soufriere and Eyjafjallajokull Hills in Iceland.

Looking back through history, some of the most destructive earthquakes ever recorded were in China, causing more than half a million victims.

One of them was in the 1550s in an area with a lot of people and buildings constructed not to withstand earthquakes.

Most recently, the Tangshan earthquake of 1976 killed more than 242,000 people.

“In general, places where major earthquakes occur and places with high population density, such as Japan, Indonesia, and China,” he says, “these are the places where you can experience devastating earthquakes.”

“Small earthquakes can cause devastation too. They don’t need their strength to be nine earthquakes – you can have 7 / 7.5 earthquakes capable of destroying cities.

“The 2004 Boxing Day earthquake and tsunami also killed nearly 200,000 not only in Indonesia but throughout the wider region – Sri Lanka and Thailand.”

Dr Bapti says science has definitely “moved forward” in terms of predicting earthquakes.

However, we are still not good at making one-off predictions.

Long term outlook

“We couldn’t say, for example, that there will be a magnitude 7 earthquake in Los Angeles on March 3, 2021,” he says.

“These kind of one-time predictions for either volcanoes or earthquakes, we are not very good at and we may not be able to predict earthquakes just because they are completely random.

But we are much better at making long-term forecasts.

“Over time periods of 50 years or 100 years – those time periods – we can determine the probabilities of earthquakes and the probabilities of how strong those ground movements will be.

This means that within these time scales, we can begin to properly engineer buildings and take measures to prepare people so that people know what to do in the event of an earthquake.

Buildings must be at least resistant. You can only get average over longer periods of time and preparation.

“Preparation is clearly a very expensive process as well.

“Countries that are well prepared for earthquakes like the United States or Japan or even South American countries like Chile – they are relatively rich countries while the poorest countries have a lot fewer resources to put into this kind of thing. There are a lot of economic and social reasons that make people not well prepared for earthquakes. “.

Do major earthquakes return to Scotland?

While typical residential housing in Scotland is not designed with earthquakes in mind due to the risk of it decreasing over the life of a residence, sensitive structures such as nuclear power plants and dams are built with earthquake resistance in mind.

But given enough geological time, could what we call Scotland again be struck by massive earthquakes at some point in the distant future?

It is possible, and there are a number of reasons why we might have it, says Dr Bapti.

“If we think about plate tectonics and plate motions at this type of time scale and where we are now, if plate boundaries are to form near Scotland or near the United Kingdom, then surely we could begin to experience many earthquakes.

The most likely scenario for this is what we call a subduction zone opening up at the edge of the Atlantic Ocean – the Atlantic plate being pushed down under the European plate – so something like this isn’t impossible on this kind of time scale.

“ The other interesting thing maybe is if there’s another Ice Age.

“If there was an ice sheet over the United Kingdom or over Scotland like there was about a million years or so, that could alter the seismic activity due to the loading.

“Especially if the ice sheet forms and melts again, you could in theory actually see much higher levels of earthquake activity as a result of this equilibrium rebound or the process of ice retreat.”

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