Subsidence in Developing Cities

Lead Supervisor: Dr Luke Bateson

Location: British Geological Survey, Shallow Geohazards and Earth Observation: Geodesy and Remote Sensing

Duration: 6 weeks

Suitable undergraduate degrees: Earth Science / Environmental Science

Project background

Multihazard and resilience science within the new British Geological Survey strategy focuses on “Risk mitigation and adaption through monitoring, characterisation and forecasting of hazardous processes and their impacts.” There is a need to understand the contribution that the lowering of the ground surface, through natural geological phenomena, can potentially make to estimates of sea level change. This is especially relevant to these coastal lowland areas, which tend to be highly populated and will experience the largest impact of sea level rise, but are also the most geologically susceptible to subsidence. With climate change forecasts indicating an increase in the frequency and intensity of winter storms and other adverse weather events these more susceptible, lower lying, coastal areas are more at risk of coastal flooding and inundation. It has been estimated that 23% of the world’s population lives both within 100 km distance of the coast and at <100m above sea level, population in coastal regions is about three times higher than the global average and include some of the most rapidly expanding cities on Earth..

Interferometric Satellite Aperture Radar (InSAR) is an Earth Observation technique which uses repeat satellite radar images of the same area to derive very precise (1-2mm/yr) measurements of ground displacements for a period of time. Typically, millions of measurement points are derived for a city each with an associated time series of motion. Analysis of this data in conjunction with geological, high resolution optical and other ancillary data enable an understanding of the likely mechanisms of motion.

As part of our International Geoscience Research and Development (IGRD) programme we aim to understand and characterise the mechanisms of subsidence in the worlds most rapidly developing cities. Such cities are often low lying and build upon poorly consolidated sediments; the combination of these factors and anthropogenic processes means they are subject to the combined effects of sea level rise and rapid subsidence. It is therefore important to not only understand what is causing the subsidence but also to quantify the rates of subsidence related to each mechanism; such understanding will enable forecasting of subsidence as the city grows and therefore enable mitigation measures to be put in place.

Within this project the student will study rapidly developing cities (most likely in SE Asia, although the city is yet to be decided) they will focus on finding areas of subsidence relating to the building of the city (typically related to the loading of the soft sediments).  For these areas of subsidence, the following will be studied: possible mechanisms for observed ground motions, areas where the ground motion relates to the construction of the city, rates of motion for each year following the growth of the city will be extracted. Extracted rates of subsidence will then be added to the database of development related subsidence being established within the Subsiding Cities IGRD project.

Programme of work:

• Literature review of subsidence mechanism for the city/surrounding area
• Introduction to satellite InSAR ground motion data, how it is produced and what to consider when interpreting it.
• Source input data and create project GIS
• Interpretation of InSAR ground motions to identify subsidence mechanisms
• Extraction of statistics of building loading related ground motions