Detecting and monitoring small-scale discrete ground movements across London, using Persistent Scatterer InSAR (PSI)

Abstract

The geology of London is surprisingly poorly understood and, until recently, has been accepted as that of an unfaulted subsiding intraplate basin. The detection of deformation in such quiescent intraplate regions is, however, rather difficult since the movement rates are at least an order of magnitude less than those at plate margins. Growing evidence from across the capital indicates that Londons ground conditions are considerably more complex than expected and that faulting is almost always involved. PSInSAR is a developing technique widely used to detect and monitor ground subsidence, especially in urban settings, the movements of which may be up to tens of millimetres. This work focuses on the detection of smaller scale ground movements (of a few millimetres), which we believe are caused by fault-controlled intraplate adjustments, using PSInSAR. The London PSInSAR dataset derives from an imaging SAR archive spanning 18 years (1992 - 2000 and 2001 to 2010). Our preliminary findings have revealed systematic patterns of both vertical and horizontal ground displacement. These displacements appear to be fault constrained and fit the predicted framework of Caledonian, Variscan/Alpine structures known to exist across southern Britain. More detailed analysis has revealed some surprising patterns, which hint at discrete movements rather than continuous creep over the 18 year period; we believe these are driven by basement faults beneath an inverting London basin.