Low magnitude earthquakes in Scotland, Highlands and Inner Hebrides

[Astronuc]

An earthquake measuring 2.1ML on the Richter scale has hit parts of the Highlands.

The event was felt just before 15:30 on Saturday in Mallaig and Morar and by islanders on Lismore in the Inner Hebrides.

Morvern, Inverness (postal town Oban) in on a peninsula overlooking the Sound of Mull to the south and Loch Linnhe to the east.

https://www.msn.com/en-us/news/world/loud-rumbling-sound-as-earthquake-hits-highlands/ar-AA1lgStT
https://www.heraldscotland.com/news/23979845.scotland-earthquake-morvern-highlands-hit-quake/
https://en.wikipedia.org/wiki/Morvern

Since 10 October, Morvern has been hit by 10 earthquakes.

On 3 December, a quake measuring 1.1ML was recorded, and all the previous ones were smaller.

I wonder if stress is building up, which would mean stronger earthquakes in the future and/or increased seismic activity.

Scotland's largest known earthquake came 64 years later (from an earthquake in 1816), in November 1880.

The 5.2 local magnitude (ML) quake in Argyll was felt along the west coast of Scotland and out east as far as Perthshire.

https://www.bbc.com/news/uk-scotland-highlands-islands-55144501

August 1974 saw a 4.4ML earthquake which had its epicentre in Kintail in the north west Highlands.

British Geological Survey (BGS), which records seismic activity across the world, detects up 300 quakes every year in the UK.

Only about three of these events are usually felt by people or are heard as a deep rumbling sound or a loud bang.

In August last year, people reported windows rattling and house beams creaking during a small earthquake on the Isle of Skye.

In the UK, the most recent of these was a 5.2 magnitude earthquake was in February 2008 which was felt across England and parts of Wales. A man suffered a broken pelvis when a chimney collapsed in South Yorkshire.

I did not know this.

Developing new seismic hazard maps for the UK​

https://www.bgs.ac.uk/news/developing-new-seismic-hazard-maps-for-the-uk/
S snd SE Wales has the highest hazard potential. The rest of Wales and Inverness (maybe parts of Argyll too) & Inner Hebrides, Scotland have about the same potential.See also - https://www.bgs.ac.uk/

 

[Baluncore]

Maybe it has something to do with an unloading reaction to Aggregate Industries' Glensanda Quarry.
56.587817°, -5.565124°

 

[Astronuc]

Maybe it has something to do with an unloading reaction to Aggregate Industries' Glensanda Quarry.
56.587817°, -5.565124°

Maybe.

I found a source of information which gives the epicenter and depth.
https://www.volcanodiscovery.com/ea...4664/mag2quake-Dec-9-2023-United-Kingdom.html

Date & time	Dec 9, 2023 15:18:19 UTC - 1 day 3 hours ago
Local time at epicenter	Saturday, Dec 9, 2023 03:18 pm (GMT +0)
Status	Confirmed
Magnitude	2.1
Depth	7.0 km
Epicenter latitude / longitude	56.616°N / 5.591°W Highland, Scotland, United Kingdom

That's very close to Glensanda Quarry - a difference of 0.02812° lat, 0.026° long, which puts the epicenter slightly NW of the quarry at about 3-4 km (~2-2.5 miles).It seems the quake was much larger, or felt more widely, than a local unloading. The news mentions Mallaig and Morar, which is much further north, and not even in Morvern. Lismore, which sits in Loch Linnhe, is much closer (Clachan, Lismore about 5 miles or 8 km from Glensanda on the coast). Morar is about 40 miles (64 km) NNW from Glensanda.

 

[Baluncore]

The earthquake was quite deep at 7 km, but the epicentre was only 3.5 km from the Glensanda Quarry.

There is another contender, a new dam, 2 km from the epicentre, that was filled with water by 2007. Earthquakes can be expected to occur following the filling of new reservoirs.

New UK dam granted preliminary certificate. 11 February 2005.
Loch Uisge dam, built by main contractor Amco for Scottish & Southern Energy, has a capacity of over 700M litres and will act as the headpond storage for the Kingairloch hydro power scheme.
https://www.waterpowermagazine.com/news/newsnew-uk-dam-granted-preliminary-certificate

The reduction in mass at the quarry, is on the opposite side of the epicentre, to the increase in mass due to the dam. That makes for an interesting change in shear, following the unloading at the end of the last glaciation.

The earthquake was well below sea level, so it is hard to see how water from the new dam could have been a trigger, other than simply as a local mass.