OR/18/054 Motion characteristics of the wider area

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Bateson, L, and Novellino, A. 2018. Glasgow Geothermal Energy Research Field Site - Ground motion survey report. British Geological Survey Internal Report, OR/18/054.

Motions within the Sentinel 1 Glasgow data can be linked to the following processes:

  1. Compaction of superficial deposits, in particular alluvium
  2. Volume change of superficial peat deposits
  3. Anthropogenic activities:
  1. Sand and gravel quarrying
  2. Slope instability of engineered slopes associated with extractive industries

Compaction of superficial deposits in particular alluvium[edit]

Vertical motions in Glasgow highlight a small-scale trend for subsidence along the alluvium deposits of the Clyde (Figure 13). These are hard to pick out without the use of a suitable colour scale. The production of a motion cross section (Figure 13) highlights the subsidence seen across the Clyde alluvial deposits.

Figure 13    General patterns of motion in Glasgow as shown by the TRE ALTAMIRA SqueeSAR™ processed S-1 data (top). Note the predominance of pale yellow colour along the Clyde indicating subsidence probably due to the compression of alluvium (middle). A cross section of the linear InSAR velocities (bottom) across the alluvial sediments highlights the increase in average rates of subsidence associated with the river sediments. Contains © TRE ALTAMIRA 2018 data, Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL. Contains British Geological Survey materials © UKRI 2019.

Volume change of superficial peat deposits[edit]

An apparent spatial correlation exists between areas of Peat and areas of ground motion, as shown in the TRE Sentinel 1 vertical dataset. Areas of subsidence seen in the North, South and North East of the area processed all overlie areas of peat as shown in Figure 14. The mechanism for the revealed ground motions is likely to be volume changes within the peat in response to changes in its water content and/or loading.

Figure 14    (centre) — TRE ALTAMIRA SqueeSAR™ Sentinel 1 average vertical motions for (2015–2017) and (right) — GVL Sentinel 1 LOS motions compared to the superficial geology (left). Black circles indicate where motion overlies areas of superficial peat. Red box shows area of detail in Figure 15. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Contains British Geological Survey materials © UKRI 2019.

The relationships to the superficial peat are clear when the area is examined in more detail (Figure 15). For example to the east of Cumbernauld there is a clear spatial relationship between the peat and the area of vertical motion. Note the similarities between the TRE and GVL InSAR results. Comparison with Coal Authority mining data (http://mapapps2.bgs.ac.uk/coalauthority/home.html) shows that there was no coal mining activity in this area.

Figure 15    TRE ALTAMIRA SqueeSARTM (top) and GVL (bottom) S-1 average motions for (2015–2017) overlain on the superficial geology for the Cumbernauld area. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Contains British Geological Survey materials © UKRI 2019.

These areas of peat-related ground motion typically have average linear rates of subsidence of 10/15 mm per year. The trend of this subsidence is linear (Figure 16) and may be either negative or positive depending on the moisture change. Removing the linear trend reveals a variation of approximately 5–6 mm over a 2 month period, this roughly bi-monthly cyclicity may be related to moisture changes within the peat.

Figure 16    (left) Time series for a single point within the subsiding peat area (see Figure 15) showing an overall linear pattern of subsidence. (right) De-trended plot of the same time series showing the roughly bi-monthly variability in the ground motion.

The area to the east of Cumbernauld undergoing uplift has average linear rates of uplift of 10–15 mm per year and the time series shows that the character of the motion is largely linear over the time period March 2015 to November 2017. The overall pattern of uplift is linear (Figure 17), however de-trending the time series shows there is some variability as the peat contracts and responds to water inputs.

Figure 17    (left) Time series for a single point within the uplifting area (blue points in Figure 15) showing an overall linear pattern of uplift. (right) De-trended plot of the same time series showing the roughly bi-monthly variability in the ground motion.

Anthropogenic activities: sand and gravel quarrying[edit]

There are several prominent areas of subsidence shown in the Sentinel 1 InSAR results from both TRE Altamira SqueeSAR™ results and GVLs ISBAS results. Many of these relate to active and/or former sand and gravel extraction sites, subsidence associated with these is likely to be caused by settlement of infilled ground or motion of slopes produced by the quarrying process.

Figure 18    (top) TRE ALTAMIRA SqueeSAR™ Sentinel 1 average vertical motions for (2015–2017) with areas of anthropogenic induced motions highlighted by black circles. (bottom) GVL Sentinel 1 average LOS motions for (2015–2017) with areas of anthropogenic induced motions highlighted by black circles. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL.

The following figures highlight the detail of motion features highlighted in Figure 18:

Figure 19    TRE ALTAMIRA SqueeSAR™ S-1 average vertical motions for (2015–2017) for the Pickerstonhill area (area 1 on Figure 18). The OS map and aerial photography shows that the subsidence is associated with quarrying sites and remediated quarrying sites. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL. Aerial photography © UKP/Getmapping Licence No. UKP2006/01.
Figure 20    (left) and (centre) — TRE ALTAMIRA SqueeSAR™ S-1 average vertical motions for (2015–2017) for the Airdrie area (area 2 on Figure 18). The OS map and aerial photography shows that the subsidence is associated with settlement of infilled ground following landfill of former quarry sites. (right) GVL Sentinel 1 average LOS motions for the same time and location. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL. Aerial photography © UKP/Getmapping Licence No. UKP2006/01.
Figure 21    (left) and (centre) TRE Altamira SqueeSAR™ Sentinel 1 average vertical motions for (2015–2017) for the Townhead area (area 3 on Figure 18. The OS map and aerial photography shows that the subsidence is associated with settlement of infilled ground in a former extraction site, subsidence to the south relates to development of a former extraction site and subsequent settling of in-filled ground. Right: GVL Sentinel 1 average LOS motions for the same period and area. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL. Aerial photography © UKP/Getmapping Licence No. UKP2006/01.
Figure 22    (left) and (centre) TRE Altamira SqueeSAR™ Sentinel 1 average vertical motions for (2015–2017) for the Broomhouse area (area 4 on Figure 18). The OS map and aerial photography shows that the subsidence is associated with settlement of infilled ground in a former extraction site. (right) GVL Sentinel 1 average LOS motions for the same period and area. Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Ordnance Survey data © Crown copyright and database right 2018, license number 100021290 EUL. Aerial photography © UKP/Getmapping Licence No. UKP2006/01.

Anthropogenic activities: slope instability of engineered slopes associated with extractive industries[edit]

Figure 23    (left) TRE Altamira SqueeSAR™ Sentinel 1 average vertical motions for (2015–2017) for the Airdrie area (area 5 on Figure 18). The aerial photography shows the motion is associated with engineered slopes. (right) GVL average LOS motions for the Sentinel 1 (2015–2017) for the Airdrie area (area 5 on Figure 18). Contains © TRE ALTAMIRA 2018 data. Contains © Geomatic Ventures Limited 2017 data. Aerial photography © UKP/Getmapping Licence No. UKP2006/01.