Earthquakes in the Inverness Area, 1995

I have left a previous post with a little conundrum, what could explain the time discrepancies and frequency surrounds the Earthquakes of the 19th century.

Well the answers are simple, the “great shake” was the initial shock in February 1818, and the area had suffered numerous aftershocks since.  The following fascinating report sheds light on this and other seismic events around Inverness.  It can be found at: http://www.invernessroyal.highland.sch.uk/resources/earthquakes.html.

Earthquakes in the Inverness Area

by Robert Preece
Ex Principal Teacher of Geography

The following is summarised from an article in the Scottish Association of Geography Teachers’ Journal, No. 24, 1995. Copyright: Robert Preece.

Although most people would admit to knowledge that Inverness lies on the Great Glen Fault, few, even local, people would admit to any possibility of experiencing earthquakes in or around the town. In some ways this is not surprising as the last earthquake centered close to Inverness was in 1934. But information from historical sources provides us with considerable evidence of earthquakes in the l9th and first half of the 20th century.

Before turning to the reports of the earthquakes themselves, it is worthwhile looking at evidence of the nature of the faulting along the Great Glen.

The Great Glen Fault

Every Scottish geographer (and almost every geography pupil) is aware of this fault as one of the three major faults on the Scottish mainland.

The fault is in fact much longer than just from Inverness to Fort William, and it is obvious even from an examination of the coastlines, that the fault continues a long distance south-westwards towards Nothern Ireland, and a distance northeastwards along the Caithness coast, but probably not as far as Shetland.

However, when looking at seismic activity along the Great Glen fault, it is important to remember two other things:

i. the present form of the Great Glen owes at least as much to the Pleistocene glaciation as it does to the wrench faulting; and
ii. there are several other, although less well-known, faults running roughly parallel to the Great Glen. Far to the north-west is the Moine Thrust, but much nearer to the Great Glen, in two nearby river valleys, the first to the north-west in Strathglass, the second to the south-east in Strathdearn, are other major faults which may still be seismically active at least in some minor way.

Earthquakes felt in the Inverness area since about 1750

Date Intensity (MSK) Notes
24 August 1768 5 only caused very minor damage; epicentre doubtful
13 August 1816 7 also minor shocks over 2 years; epicentre could have been well west of Inverness
2 February 1888 5-6 originally epicentre thought to be near Inverness, but now thought to be in Glen Garry (west of Fort Augustus); at least 47 aftershocks
15 November 1890 6 18 aftershocks in next month; epicentre in the hills west of Inverness
18 September 1901 7 3 foreshocks and about 50 aftershocks over next 2 months, one reaching intensity 5; epicentre at Dochgarroch (7 km SW of Inverness town centre)
16 August 1934 5+ epicentre now thought to be west of Dingwall in Wester Ross

The 1768 earthquake

As there was no Inverness newspaper at that time, the report, taken for the Aberdeen Journal from the Edinburgh Advertiser, says “two shocks of an earthquake were felt over the whole town of Inverness, which did no other damage than breaking a few empty bottles, and shaking the pewter plates from the shelves”. This clearly was a relatively minor earthquake. It is not possible with such limited evidence to determine an accurate location for an epicentre.

The 1816 earthquake

This is in many ways the earthquake with the most interesting reports, partly in view of the nature of the language of the time, and partly for the type of information supplied. The earthquake was probably the second most severe on record, falling only slightly behind the intensity of the 1901 earthquake.

The Caledonian Mercury reports that two men walking near to Carnoch (NGR NH 2551) at the head of Strathmeig fell over due to the shock. Quite why two men should be walking the hills at 10.40 pm – presumably GMT – even on an August evening, is not explained. As they fell on their backs, it is claimed that the shock came from the west. If the shock had come from the east, i.e. from the Great Glen area, it is claimed that they would have fallen forward. However, this means that there is an interesting possibility that the epicentre was not in the Great Glen but much farther west, where population is so sparse that there were few reports of the earthquake.

The top of the steeple of the Inverness jail was damaged, and was not repaired until 1828.

The 1888 earthquake

This earthquake took place at about 5 am on 2nd February, but even in 1888 the Inverness Courier reporter comments on the difficulty of giving an accurate time “unless the relation of clocks and watches to Greenwich time were accurately determined”. There are no reports of damage. There were two foreshocks and at least 47 aftershocks, lasting until December 1889. Browitt et al thought that the epicentre of this event was at Invergarry, some distance south-west of the southern end of Loch Ness, and about 50 km south-west of Inverness town, although obviously still on the Great Glen Fault. This would account for the effects in Fort William being recorded as relatively severe. However, Musson et al now propose an epicentre in the upper reaches of Glen Moriston, near Loch Cluanie.

The 1890 earthquake

This earthquake also seems to have had a significant number of aftershocks, with the main shock and the first four of the aftershocks occuring in the first thirty hours on l5th and 16th November, the first aftershock being only 25 minutes after the main shock. There are reports of minor damage. As with many other reports over the years, the general claim is that the movement occured from south-west to north-east, or the reverse way. This of course is the same as the orientation of the Great Glen, but also suggests an epicentre to the south-west of the town. The epicentre, based on mapping of the intensity of both the main shock and the aftershocks, would appear to have been in the hills south-west of Inverness, possibly on one of two minor faults in this area.

The captain of a schooner in Inverness harbour reported that at the time the tide was out and the vessel aground, meaning that the shock was felt quite strongly. The ferryman of the Kessock Ferry (from Inverness to the Black Isle) reported that they found their boat suddenly driven along toward the shore. A correspondent from Beauly, some 15 km to the west of Inverness, reported the awful screeching of the pheasants in the woods. “Many dogs, too, shook with fear, and howled piteously, refusing to be comforted”.

The 1901 earthquake

Although there is a report of a minor earthquake in November 1893 (which was linked with earthquakes at the same time in Canada and the United States), the next major event was September 1901. This is probably the most severe of the earthquakes to affect Inverness.

Due to publication dates of the Inverness Courier, the Edinburgh papers carried the first news of the event. The seismograph at the Royal Observatory in Edinburgh failed to pick up the shock, apparently due to the orientation of the boom of the instrument. However Musson et al think it is more likely that the instrument was not sufficiently sensitive to the particular frequency of the vibrations. Nevertheless the shock was distinctly felt as far south as Fife. As the event took place at 1.24 am, most people were in bed. A lot of minor damage was done to buildings, and a couple of minor buildings collapsed, in one case injuring a horse.

However, the most interesting report comes from Dochgarroch, some 8 km south-west of Inverness and lying very close to what was probably the epicentre of the main shock.

Mr Munro, schoolmaster at Dochgarroch, is reported as saying:

“The earthquake left its mark both on the Schoolhouse and on Dochgarroch Lodge, tenanted by Colonel Mackinnon. In both some of the cans were thrown down and the stonework of the chimneys cracked. In the walls of the schoolhouse there are perceptible cracks from top to bottom. In the gable of the classroom there are two distinct cracks, and nearly every ceiling in the house is cracked . . . Most peculiar of all is a crack on the north side of the (Caledonian) Canal bank, extending 200 yards to the east of the Locks and 400 yards to the west. It is in the middle of the towing-path, in the hard-packed surface, and is nearly half-an-inch wide.”

Enquiries to the current occupants of the schoolhouse, and to the school itself, concerning the damage to the buildings brought surprise and total ignorance of the 1901 earthquake.

The 1934 earthquake

This earthquake, on 16th August, was one of the less severe events, and attracted relatively little press attention in Inverness, even though it was felt throughout a very large area in northern Scotland and the Outer Hebrides.

Re-examination of the evidence by Musson et al now relocates the epicentre of this earthquake somewhere in Wester Ross, some considerable distance west or north-west of Inverness. The drawing of isoseismal maps, based on newspaper evidence of the effects in different communities, suggests a Great Glen epicentre to be unlikely. Also there is some fairly reliable evidence of aftershocks felt in Inverasdale, near Poolewe.

The shocks appear to have been particularly felt in the Inverness area by the night-shift workers at the Foyers aluminium smelter beside Loch Ness. No damage seems to have been reported from anywhere in the district, although the shock was felt as far away as Badenoch to the south-east, and the Isle of Skye and beyond to the west. According to a report in The Times several women in Dingwall fainted and one had to receive medical attention.

Other reports of earthquakes in Inverness district

One event which is always recalled is that, at the time of the great earthquake in Lisbon in 1755 which destroyed the city, Loch Ness rose and fell. Simpson, in his review of earthquakes after the 1934 shock, writes as follows:

“. . . There is no record of anything in the nature of an earthquake having been felt at Inverness at that time, but there is no doubt that at the moment of the great disaster at Lisbon, when a great part of the city was destroyed, with 20,000 of the inhabitants, the waters of Loch-Ness underwent an extraordinary upheaval, rising three feet above their highest point in spring floods, almost covering the glacis (part of the fortifications) at Fort-Augustus, and throwing a boat laden with wood far on the shore. The lake in a short time assumed its usual level.”

The Lisbon earthquake was probably one of the most severe in historic times. Modern interpretation of the evidence suggests a shock of perhaps 8.9 on the Richter scale. The effects on Loch Ness were an example of a seiche, and these usually take place along the longest diameter of a lake. Loch Ness is of course ideal for this sort of event, being long and narrow, and also being roughly aligned with the direction from which the shock waves would have come. Loch Lomond was affected at the same time.

Causes of earthquakes

In Inverness there is still a very real possibility of an earthquake, possibly in the very near future. The Kessock Bridge, opened in 1982 and taking the A9(T) road north from Inverness, crosses the line of the Great Glen fault under the Moray / Beauly Firth. In consequence it has been built with seismic buffers, and these were planned during the design stage of the bridge.

These buffers are at the north abutment, nearly over the line of the fault, and they supplement longitudinal restraint at Pier 7, the south main pier. Each buffer is just over 3 metres long and weighs about 2.5 tonnes. Under slowly applied loads the buffer is easily extended or retracted, whereas under suddenly applied shock (such as during an earthquake) there is high resistance to movement. Basically the buffers are large hydraulic pistons.

Conclusion

Modern theory on the causes of earthquakes will be known to most readers of this article, but it is clear that Inverness will never experience major earthquakes on the lines of the activity on, for example, the San Andreas Fault. Only three events, namely 1816, 1890 and 1901, can be regarded as earthquakes taking place near Inverness, and there is even doubt concerning the 1816 event. However, there is still a real possibility of an earthquake to the order of 5 or 6 on the MSK scale in the area. As to the practical consequences of this, there is no need to incorporate any major specialised design features into normal buildings in the area, and it is very unlikely that there will be any immediate need to build any major bridges, along the lines of the Kessock Bridge, across the line of the Great Glen Fault, although a possible crossing of the Caledonian Canal on the southern outskirts of Inverness to complete the town ring road in the future will require to give consideration to possible seismic activity. Inverness earthquakes will in consequence be a matter of ignorance to the average citizen, until the next shock, whenever that may be.

Earthquakes in the Inverness Area, Robert Preece, Inverness Royal Academy, 1995

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