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