How accurate is your model between boreholes? Using shallow geophysics to test the best method to model buried tunnel valleys in Scotland, UK

Kearsey, Timothy; Whitbread, Katie; Arkley, Sarah; Morgan, Dave; Boon, David; Raines, Michael. 2018 How accurate is your model between boreholes? Using shallow geophysics to test the best method to model buried tunnel valleys in Scotland, UK. In: Three-Dimensional Geological Mapping - Workshop Extended Abstracts. Vancouver, Illinois State Geological Survey, 39pp. (Three-Dimensional Geological Mapping Workshops).

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The accuracy and uncertainty of geological models is becoming increasingly of interest as more and more end users rely on them for subsurface prediction. Since 2001 the British Geological Survey has published a National Superficial Deposit Thickness Model (SDTM) derived by interpolation of borehole data. It includes all deposits of fluvial, glacial, marine, residual, aeolian or anthropogenic in origin. It is know that this model is poor at identifying features such as buried tunnel valleys and overfilled bedrock depressions. Here we explore the characterisation of these features using an example from central Scotland, and test whether alternative modelling methodologies enhance our ability to predict the geometry of these features. This study we focus on the Ochil’s buried tunnel valley, east of Stirling in central Scotland. In the UK Superficial Thickness model, the Ochil’s trough is not completely resolved; there are apparent gaps in the longitudinal continuity in areas with no borehole data. To examine the degree to which the method of interpolation has affected the surface morphology, two additional interpolation methods were applied to the SDTM borehole dataset: Direct Triangulation and Implicit Geological Gridding. To test the accuracy of the different interpolation methods we used a TROMINO® passive seismic instrument to provide geophysical constraint on the bedrock surface. The results reveal that in the apparent gaps the SDTM and Direct Triangulation methods underestimated the thickness of superficial deposits by between 50-60 m. The Implicit Geological Grid, however, overestimated the thickness of superficial deposits by only 16 m. This raises the question should we consider using different gridding methods for different buried surfaces?

Item Type: Publication - Book Section
Programmes: BGS Programmes 2009 > Geology and Landscape Scotland
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Date made live: 12 Jul 2018 14:04 +0 (UTC)

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