Geological interpretation of current subsidence and uplift in the London area, UK, as shown by high precision satellite-based surveying

Abstract

Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatterer interferometry (PSI), aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100,000 years' duration.During the period 1997 to 2005, most of the region around the Thames estuary subsided between 0.9 and 1.5 mm a -1 on average, with subsidence of thick Holocene deposits being as fast as 2.1 mm a -1 . By contrast, parts of west and north London on the Midlands Microcraton subsided by less than 0.7 mm a -1 , and in places appear to have risen by about 0.3 mm a -1 . These rates of subsidence are close to values determined previously by studies of Quaternary sequences, but the combined GPS, AG and PSI land level change data demonstrate a new level of local geological control that was not previously resolvable.

Natural and Anthropogenic Geohazards in Greater London Observed from Geological and ERS-1/2 and ENVISAT Persistent Scatterers Ground Motion Data: Results from the EC FP7-SPACE PanGeo Project

“…It is also noteworthy that the width of the Thames floodplain increases markedly downstream of the Wimbledon Fault, as shown by the outcrop of the Holocene deposits. Our PSI data confirm the observations for domain '5A' identified by ALDISS et al (2014), who found velocities of -1.55 ± 0.83 mm/year for this area during 1997-2005, with the largest subsidence rates centred close to the Merton Abbey public water supply well. Ground motions in this area were attributed to groundwater abstraction from the above water well, and were investigated further in the framework of the ESA Terrafirma project, via the production of the Terrafirma-London H3 Modelled Product (BATESON et al 2009).…”

“…3.2.2). This geohazard polygon also corresponds well with domain '6C' identified by ALDISS et al (2014).…”

“…Subsidence is recorded by the ENVISAT PS results, with -0.18 ± 0.69 mm/year for the PS within the polygon, and -7.74 mm/year observed peak velocities, due to either an inversion of the motion trend or, more likely, the presence of another geohazard type, overlapped onto (and thus masking) the existing uplift. Comparison with ground motion domains from ALDISS et al (2014) suggests that the unstable area corresponds with domain '1' identified from AG- Table 2 for detailed information and PSI ground motion statistics, and Fig. 3 …”

“…Within the pre-Mesozoic basement, the Midlands Microcraton underlies the geohazard polygon. This terrane is characterised by the occurrence of Proterozoic rocks at relatively shallow depths, recorded recent isostatic uplift, and was delineated in terms of the generalised domain 'G1' by ALDISS et al (2014). Gravity data that were processed using gravity stripping to the base of the Mesozoic succession, enhanced variations in the regional Bouguer gravity anomaly field, which largely relates to Palaeozoic or Proterozoic age geological formations beneath the Chalk Group .…”

Monitoring the Response of Roads and Railways to Seasonal Soil Movement with Persistent Scatterers Interferometry over Six UK Sites

“…The rates of deformation in this study are aligned to previous investigations which have used PSI to monitor earth surface movement in the UK [18]. Apart from [20,25], there is limited work reporting investigation of the relationships between major soil group type and infrastructure movement using PSI, particularly in the UK, so limited direct comparisons can be made.…”