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

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

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

SummaryBackground Azithromycin has been proposed as a treatment for COVID-19 on the basis of its immunomodulatoryactions. We aimed to evaluate the safety and efficacy of azithromycin in patients admitted to hospital with COVID-19.Methods In this randomised, controlled, open-label, adaptive platform trial (Randomised Evaluation of COVID-19Therapy [RECOVERY]), several possible treatments were compared with usual care in patients admitted to hospitalwith COVID-19 in the UK. The trial is underway at 176 hospitals in the UK. Eligible and consenting patients wererandomly allocated to either usual standard of care alone or usual standard of care plus azithromycin 500 mg once perday by mouth or intravenously for 10 days or until discharge (or allocation to one of the other RECOVERY treatmentgroups). Patients were assigned via web-based simple (unstratified) randomisation with allocation concealment andwere twice as likely to be randomly assigned to usual care than to any of the active treatment groups. Participants andlocal study staff were not masked to the allocated treatment, but all others involved in the trial were masked to theoutcome data during the trial. The primary outcome was 28-day all-cause mortality, assessed in the intention-to-treatpopulation. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.Findings Between April 7 and Nov 27, 2020, of 16 442 patients enrolled in the RECOVERY trial, 9433 (57%) wereeligible and 7763 were included in the assessment of azithromycin. The mean age of these study participants was65·3 years (SD 15·7) and approximately a third were women (2944 [38%] of 7763). 2582 patients were randomlyallocated to receive azithromycin and 5181 patients were randomly allocated to usual care alone. Overall,561 (22%) patients allocated to azithromycin and 1162 (22%) patients allocated to usual care died within 28 days(rate ratio 0·97, 95% CI 0·87–1·07; p=0·50). No significant difference was seen in duration of hospital stay (median10 days [IQR 5 to >28] vs 11 days [5 to >28]) or the proportion of patients discharged from hospital alive within 28 days(rate ratio 1·04, 95% CI 0·98–1·10; p=0·19). Among those not on invasive mechanical ventilation at baseline, nosignificant difference was seen in the proportion meeting the composite endpoint of invasive mechanical ventilationor death (risk ratio 0·95, 95% CI 0·87–1·03; p=0·24).Interpretation In patients admitted to hospital with COVID-19, azithromycin did not improve survival or otherprespecified clinical outcomes. Azithromycin use in patients admitted to hospital with COVID-19 should be restrictedto patients in whom there is a clear antimicrobial indication

West Lothian leads in Scotland

Scotland’s first Local Geodiversity Action Plan – the West Lothian Geodiversity Framework – is nearing completion. With help from West Lothian Council, Scottish Natural Heritage and the Lothian and Borders RIGS Group, the British Geological Survey (BGS) has finished the geodiversity audit and the associated report; the GIS & database and outline action plan are well advanced. The project, funded by the Scottish Executive Aggregates Levy Fund and BGS, assesses the state of geodiversity in the area in its local to national context, and its relevance to biodiversity, soil conservation and other protection designations. The audit will inform sustainable planning and development, management, conservation and interpretation of the Earth heritage of the area

Moray Firth 3D onshore-offshore modelling

Improved 3D visualisation and interpretation of the geology of the Inner Moray Firth in North East Scotland has been achieved as a result of collaborative investigations by a team of BGS land and marine surveyors feeding combined data sets into GSI3D models. A calculated regional fault network, has been generated, incorporating data from the Great Glen-Moray Firth tectonic model, informed by detailed bedrock survey data from the coastal zone. This network has been amalgamated with cross-sections, based upon those generated for the GB3D model and by numerous additional helper sections, to produce a fully calculated model of the onshore and off shore cover sequence of the Inner Moray Firth between Inverness, Helmsdale and Portsoy (c. 8,500 km2)

Empirical assessment of the uncertainty in a 3-D geological framework model

form that can be used to support planning and decision making. However, there is little information on the uncertainty of such framework models. We report a statistically-designed experiment in which each of five geologists independently produced a framework model of a single region in the east of England. Each geologist used a unique set of borehole observations from which to make their model. Each set was made by withholding five unique validation boreholes from the set of all available boreholes. The models were then compared with the validation observations. Between-modeller differences were not a significant source of variation in framework model error. There was no evidence of systematic bias in the modelled depth for any unit, but there was a statistically significant but small tendency for the mean error to increase with depth below the surface. The confidence interval for the predicted height of a surface at a point ranged from �5.6 m to �6.4 m. There was some evidence that the variance of the model error increased with depth, but no evidence that it differed between modellers or varied with the number of close-neighbouring boreholes or distance to the outcrop. These results are specific to the area that has been modelled, with relatively simple geology, and they must also reflect the relatively dense set of boreholes available for modelling. The method should be applied under a range of conditions to derive more general conclusions, and benchmark quality measures for three-dimensional models of contrasting terranes

The 3D geological model for the Forres groundwater flood risk area [abstract only]

In recent years, the urban areas of Elgin, Nairn and Forres have been threatened by severe river flooding events leading to the expenditure of millons of pounds on the design and installation of new flood prevention measures. The most severe catastrophic flood in modern British history occurred on August 3rd 1829, along the course of the River Findhorn, which reaches the coast near Forres. Reconstructions suggest that more than 100mm of rain fell in 24 hours and peak flows exceeded 1,400 cubic metres per second in parts of the catchment. BGS studies around Forres, commissioned by Moray Council, indicate that groundwater has a significant impact on flooding particularly in the lower reaches of this ‘flashy’catchment. Targeted work has now been completed, that included detailed Quaternary mapping and geotechnical testing to supplement ground water measurements from boreholes and trial pits, to establish the permeability of the shallow geology of the catchment around Forres. A GSI3D model has been constructed of the shallow geology that has 43 separate layers. This will be demonstrated during the workshop. The model has also been reattributed with permeability values and this is now being linked to a ZOOM ground water model to produce the most detailed evaluation of shallow groundwater movements in any part of Scotland

Modelling Scottish peat stratigraphy using integrated electrical geophysics

The British Geological Survey is undertaking a holistic investigation of an upland catchment near Talla Linnfoots Reservoir in the Southern Uplands. The main aim of the study is to develop an integrated earth model of the site to aid the understanding of landscape evolution and environmental change in response to climate change over the past 12.000 years. To do this we are building an attributed 3D geological model of the site. One advantage of a 3D geological model over a conventional paper based or 2D GIS approach is the ability to generate volumetric data, for example the total thickness of peat deposits. This type of data could be useful when making landslide hazard assessments of large blanket peat bogs prior to electricity generation developments, as recognised in the recent Best Practice Guide produced by the Scottish Executive in 20061. To build the 3D geological model of the site we used traditional site investigation data, including geological and soil surveying. Initial auguring proved a variable thickness of peat over the site. Trial pits, boreholes and light-weight penetrometer techniques did not provide sufficient data density for the resolution required. Shallow geophysical techniques were applied to provide information between borings. Terrestrial LiDAR techniques were used to create a high resolution (1m cell size) Digital Terrain Model (DTM) to provide the ground surface layer to the 3D geological model. Ground investigation data was assembled in the GSI3D software package enabling the visualisation of all observations and measurements in their true 3D spatial positions. We used a combination of shallow geophysical techniques, including Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT). One great advantage of these techniques is that they provided a continuous linear dataset, which could be imported into the modelling software. Borehole and penetrometer control was used to validate and interpret the geophysical model. This study showed that the application of geophysical techniques to assessment of peatland stratigraphy enables rapid and accurate data collection with minimal environmental impact. Future work at Talla site will involve constraining the lithostratigraphic model using absolute dating techniques including C14 and cosmogenic methods. This will provide insight into the timing of de-glaciation and the onset of peat growth since the Late Glacial in the Scottish Lowlands