OR/14/050 Modelled faults

Monaghan, A A. 2014. Model metadata report for BGS - DECC shale study model, central and eastern Midland Valley of Scotland. British Geological Survey Internal Report, OR/14/050.

The DECC model contains only the 19 largest, regional-scale faults with throw greater than approximately 200–400 m, and/or length greater than 8 km, in the central and eastern Midland Valley of Scotland (Table 2). These are predominantly the largest, basin-bounding structures with throws up to 1800 m. Some of the modelled faults with the smallest throws such as the Comedie and Abbey Craig faults (see Figure 1) occur within the Carboniferous basin, and were included as they were well constrained by seismic and mining data. Other faults with similar throws may be present, but have not been included in the model due to lack of data constraint. Numerous faults with throws less than 200–400 m are known but have been excluded from the regional-scale model. An additional 7 faults, such as the Highland Boundary and Southern Upland faults, that are not within the DECC area of interest have been included in the model files (Table 2) as they provide a useful context for the overall basin structure.

Fault extents are taken largely from DiGMap 1:50 000 scale with dips taken from a variety of seismic interpretation, mine plan data and BGS memoir descriptions (Table 2).

Table 2    Summary of fault information and dips used to create modelled faults
along with inclusion and exclusion criteria

Fault name	Source	Outside DECC AOI
Highland Boundary	MVS2012/13 model (Monaghan, 2013).	x
Southern Upland	MVS2012/13 model (Monaghan, 2013).	x
West and East Ochil	MVS2012/13 model (Monaghan, 2013). Where these faults are picked on seismic lines it is consistent with the existing, simplified modelled fault.
Campsie	MVS2012/13 model (Monaghan, 2013) with an edit — deleted east end where not proven or the fault is proven with much shallower dips in mining/seismic data and small offset, possibly a different structure.
Dura Den	MVS2012/13 model (Monaghan, 2013).
Dusk/Lugton Water	MVS2012/13 model (Monaghan, 2013).
Inchgotrick	MVS2012/13 model (Monaghan, 2013).	x
Kerse Loch	MVS2012/13 model (Monaghan, 2013).	x
Revised Dechmont	Extended to greater depth (-5000 m) than in previous versions, dip of 75° (previous version had the northern segment at 90°). Suggestions from seismic picks of an extension to north or an extension and splay to the south have not been incorporated, as there is no map/mine evidence for this in the higher resolution Glasgow models.
Milngavie-Kilsyth	MVS2012/13 model (Monaghan, 2013).
Pentland	MVS2012/13 model (Monaghan, 2013).
Lammermuir	MVS2012/13 model (Monaghan, 2013).	x
Archerfield	Forth Approaches and MVS2012/13 model (Monaghan, 2013). Only the far eastern end of the fault is within the AOI but there is no seismic evidence to constrain it here, so it has been excluded.	x
Crossgatehall	CASSEM (Monaghan, 2012). The DECC seismic interpretation has steeper dip on this fault than previously modelled but as the seismic data quality is poor the existing modelled fault has been used.
Firth of Forth	CASSEM (Monaghan, 2012). The fault is only interpreted below the horizons modelled here and so does not affect the modelled horizons.	x
Roslin-Vogrie	CASSEM (Monaghan, 2012). The current seismic line interpreted position is slightly different than the mapped position, though with similar dip. The well-constrained mapped position is taken in preference as the seismic data are poor quality.
Dunbar-Gifford	CASSEM (Monaghan, 2012).
Rosyth	New interpretation, dip assumed 60° to north. From +1000 to -5000 m. Eastward extension of this structure was examined but not supported by seismic interpretations in the Forth Estuary.
Abbey Craig	New interpretation constrained by map and mining data with a 55° dip. Seismic picks not wholly honoured as they indicate a complex non-planar structure, without enough constraining data to adequately define such a structure.
Colinton-Murieston	New interpretation combining the Colinton and Murieston mapped faults for the purpose of a simplified structure for modelling. Dip assumed 60°.
Banknock	Modified existing interpretation to produce a simplistic structure with 80° dip using the map trace. Seismic interpretations indicate a non-planar structure but without enough data constraint to define such a structure. (the southerly bounding fault of the small ‘Forth Graben’ was not included as the throw appears to die out quickly laterally and was not consistent with the seismic interpretation).
Wilstontown	New interpretation from map and seismic data, dip of 50°. Seismic picks suggested the western end of this fault was offset by a NW-trending structure and continued further west than currently modelled. This local complexity was not included in the regional model, the fault was terminated where truncated by the NW-trending fault.
Comedie	Modified the dip of the existing modelled Comedie Fault to 50° based on seismic interpretation. This does not quite fit all mining/seismic data but is the best planar fit.
Bothwell	New interpretation, modified the mapped ‘Bothwell Fault’ trace (Forsyth et al., 1996) to match the well-constrained seismic interpretation trending slightly more to the ENE. Dip of 60°.
Clarkston-Castlemilk	New interpretation to bound the Clyde Plateau Volcanic Formation south of Glasgow. Dip 60°. ‘Gleniffer Fault’ western segment subsequently not included due to this being a very complex fault system (though the modelled fault name is still called Gleniffer-Castlemilk).

Faults which were considered but excluded due to poor or inconsistent constraining datasets, or having only short segments with throws of a few hundred metres, include the Middleton Hall and Ochiltree Fault in West Lothian, the Leven Fault in Fife and the Slammanan Fault in the Central Coalfield.