Geological Fault

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Dear British Geological Survey,

Please can you provide all information you have on the Hunterston-Largs Fault line in Ayrshire Scotland.
Information requested, is length of fault, depth of fault, width of fault, age of fault and all earthquakes caused by this fault, moments of the fault, exact co-ordinates of the fault line and any other data you have.

Yours faithfully,

Peter

enquiries, British Geological Survey

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enquiries, British Geological Survey

Dear Peter

Our ref: IDA 258347

Thank you for your request made under the Freedom of Information Act 2000. Since your request concerns environmental information we will be handling it under the terms of the Environmental Information Regulations 2004. We normally expect to reply within the standard time period of twenty working days but under complex circumstances it could take up to forty working days. We will let you know if this is the case as soon as possible.

Please do not hesitate to contact me if you have any queries about this request and please quote the reference number above in any future communications.

Rachel Cartwright MSc MCLIP
Enquiry Service Manager
British Geological Survey
Keyworth
Nottingham
NG12 5GG

Tel: 0115 936 3143
[British Geological Survey request email]
www.bgs.ac.uk

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enquiries, British Geological Survey

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Dear Peter

 

Our ref: IDA 258347

 

Thank you for your request made under the Freedom of Information Act. 
Since your enquiry concerns environmental information it has been
considered under the terms of the Environmental Information Regulations
2004.

 

The Largs-Hunterston Fault Zone, in the Hunterston Peninsula area of
Ayrshire

 

The fault system in the Hunterston Peninsula area as it is shown on the
published 1:10,000 scale geological map (NS14NE) is referred to in the
geological literature as the “Largs-Hunterston Fault Zone”. In this area
the fault zone forms the boundary between the Upper Devonian Seamill
Sandstone Formation and Lower Devonian Portencross Beds. Further to the
north-northwest the fault juxtaposes the Seamill Sandstone Formation
against the Kelly Burn Sandstone Formation; both formations are Upper
Devonian in age.

 

At Farland Head the fault zone has been mapped as comprising three
essentially NNE-SSW-trending brittle faults. The eastern-most fault occurs
on the eastern side of Farland Head where the headland meets Ardneil Bay.
On the geological map (sheet NS14NE) this fault shown as being cut by an
east-west-trending tholeiitic dolerite dyke of Permo-Carboniferous age.
There is no obvious offset shown of this dyke shown (either on the map or
accompanying reports) as it crosses this fault strand, indicating that
there has been no significant movement on the eastern strand of the fault
system since Permo-Carboniferous times. The western most faults form the
margins of a small inlet known as Sandy’s Creek. The projection of these
faults inland of the coast on map sheet NS14NE indicates that these
brittle structures merge to form a single fault the east of Portencross.
In this area the fault is cut by an approximately northwest to
southeast-trending quartz-dolerite dyke of Permo-Carboniferous age. There
is no mapped offset of this igneous intrusion, indicating that there has
been no significant movement on the western strand of the Largs-Hunterston
Fault Zone since Permo-Carboniferous times.

 

The presence of dykes cutting through the strands of the Largs-Hunterston
Fault Zone in the Hunterston Peninsula area provide clear evidence that
this fault has encountered very little or no significant movement since
Permo-Carboniferous times. As noted above the fault zone is responsible
for the juxtaposition of Lower and Upper Devonian strata (downthrow to the
west/northwest), but this movement predated late Carboniferous-Permian
times and probably occurred during or immediately after the deposition of
the Devonian Old Red Sandstone Succession.

 

On the published 1:10,000 scale geological map sheet NS15SE the line of
the westernmost fault strand of the curves slightly towards the north as
it is projected to the north. This fault is shown as terminating
immediately offshore within Hunterston Sands and has a total mapped strike
length of c. 4 km. The eastern strand of the Largs-Hunterston Fault Zone
is projected north-eastwards across the sheet and into the adjoining
1:10,000 geological map sheets NS25SW and NS25NW where it curves into a
more north-south orientated structure; resulting in a total strike length
of 9 to 10 km. On sheet NS25NW this fault is shown to terminate
immediately north of Fairlie. However an apparently separate approximately
north-south trending fault, labelled at the Largs-Hunterston Fault Zone is
shown further to the north at Bowen Crags. However, there is a marked
break of c. 1.5 km separating these two faults, consequently their exact
relationship is unknown. This break in the southern and northern
extensions of what has been referred to as the Largs-Hunterston Fault Zone
is also shown on the published 1:50,000 scale geological map of the Irvine
district and the accompanying memoir.

 

In the IGS report describing the geology of the Hunterston Peninsula the
structure of the area is described as, “The dominant faults of the
Hunterston Peninsula are those delimiting the east and west margins of the
belt of steeply dipping strata and extending north-east from Farland Head
to Poteath and beyond.”. No detailed description of the deformation
associated with these fault strand or estimates of the amount of
displacement on this fault system are published in this report. This
suggests that this fault system has very little surface expression at
Farland Head and is not exposed inland. Consequently quantifying the depth
of penetration of this fault zone and its significance in terms of its
impact on the regional structure of this part of Ayrshire is speculative.

 

Further to the above geological information, the BGS Seismology Team has
searched for earthquakes that affected the area within a 25x25km square
centred on the fault. Please note BGS never attributes any earthquake with
a particular fault in the UK, as we do not have enough events to clearly
indicate major fault lineations. Earthquakes of limited size in the UK,
due to the geological conditions, can be generated by very small faults,
only 1- 2 km long. Location uncertainties in earthquake epicentres are
typically 1- 3 km currently, and larger before 1980. Since faults are very
common in the rocks underlying the UK there may be quite a number of
candidate faults within this radius of uncertainly for those small
earthquakes.  Yet, as stated above, the Largs-Hunterston Fault has not
been active since Permo-Carboniferous times (359-252 million years ago)
and therefore none of the recorded earthquakes (first one in 1836) in the
area are likely to have been caused by this fault (see attached map and
associated data).   

 

Published geological maps

1:50 000 scale geological maps: sheet 22W (Irvine)

1:10 000 scale geological maps: NS14NE, NS15SE, NS25SW and NS25NW

 

Published reports and memoirs

Davies, A. 1972. A description of the geology of the Hunterston Peninsula,
Ayrshire. Rep. No. 72/1, Inst. geol. Sci. 6 pp.

Monro, S K. 1999. Geology of the Irvine district. Memoir of the British
Geological Survey, Sheet 22W and part of Sheet 21E (Scotland).

McLean, A.C. & Deegan, C.E. (Editors). The solid geology of the Clyde
Sheet (55°N/6°W). IGS Report 78/9.

 

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Regards

 

Rachel

 

Rachel Cartwright MSc MCLIP

Enquiry Service Manager

British Geological Survey

Keyworth

Nottingham

NG12 5GG

 

Tel: 0115 936 3143

[British Geological Survey request email]

www.bgs.ac.uk

 

 

 

 

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