Many earthquake faults remain to be discovered around the world, sometimes because they are hidden in the landscape, covered by sediments in basins. Cities are built on these basins because they offer fertile ground for agriculture and sources of water contained within the ground. However, groundwater extraction can induce significant land subsidence. Whilst a problem for housing and water supply, it provides an important opportunity to find faults beneath the city that may pose a future earthquake risk.
We can detect these faults as they preferentially control how ground water flows in the subsurface and within aquifers, and consequently exhibit a structural control on how the ground surface sinks. Using the latest Earth Observation satellites, such as Sentinel-1, this project will detect these subsidence patterns to find the hidden faults beneath major cities around the world using the technique of InSAR (Elliott, 2020). We anticipate that including horizontal as well as vertical motion will improve detection of subsidence and fault locations. This work is important because seismic hazard and hidden faults potentially affect many people in growing cities (Crowley & Elliott, 2012). Many major faults lie along the edge of mountains and basins, and accommodate the relative motion between these two tectonic domains. However, faults also form within basins as the deformation migrates through time and the fault may be hidden within the basin (Elliott et al., 2020). This research will be interdisciplinary and engage directly with disaster risk and humanitarian practitioners to tailor relevant science-based outputs for integration within disaster risk assessment and emergency scenario planning. This will therefore support the realisation of UN development goal of sustainable cities and reduced loss of life from hazards.
An improved understanding of the geomechanical effects of groundwater withdrawal and the control of faults of the flow of fluids will be gained through poro-elastic modelling (Gambolati & Teatini, 2015) placing constraints on the patterns of anthropogenic land subsidence. A step change in observing spatial and temporal patterns of deformation over regional areas is now possible with satellite radar such as Sentinel-1, with accuracies better than a few millimetres per year using InSAR. This project will use these space-based measurements of differential subsidence rates to test methods that reveal these concealed faults beneath cities in actively deforming regions. It will test the hypothesis that fault detection is greatly enhanced with the use of horizontal deformation in addition to vertical rates, both through direct imagery and computer vision analysis of the observations and in numerical models of aquifer flow. By quantifying the spatial and temporal pattern of subsidence, using such data analysis techniques as Independent Component Analysis, identification of potential hidden faults within the sediments will be possible. By comparing this to predictions of surface deformation from basin-wide compaction modelling of subsidence, the faults acting as barriers or conduits to fluid flow will be detected as these will alter the first-order subsidence signal. Once identified, the locations and sizes of faults relative to exposed urban populations will be co-designed with key stakeholders to produce applied seismic hazard and risk analyses using a scenario-based approach (Hussain et al., 2020).
The student will work under the supervision of Dr. John Elliott, within the Active Tectonics group of the Institute of Geophysics & Tectonics in the School of Earth & Environment at Leeds. The project will be co-supervised by Dr Mark Thomas (also in IGT, SEE) and Dr Kate Crowley (University of Edinburgh). The Institute of Geophysics & Tectonics at Leeds also hosts the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) which provides a large group of researchers engaged in active tectonics research with whom the student can interact. The student will also have the opportunity to engage with a wider range of scientists within COMET at a number of other UK institutions who have a broad interest in problems of active tectonics.
Crowley, K., & Elliott, J. R. (2012). Earthquake disasters and resilience in the global North: lessons from New Zealand and Japan. The Geographical Journal, 178(3), 208-215. doi:10.1111/j.1475-4959.2011.00453.x
Elliott, J. R. (2020). Earth Observation for the assessment of earthquake hazard, risk and disaster management. Surveys in Geophysics, 1-32. doi:10.1007/s10712-020-09606-4.
Elliott, J. R., M. de Michele & H. K. Gupta (2020), Earth Observations for Crustal Tectonics and Earthquake Hazards, Surveys in Geophysics, doi:10.1007/s10712-020-09608-2.
Gambolati, G., and P. Teatini (2015), Geomechanics of subsurface water withdrawal and injection, Water Resour. Res., 51, 3922–3955, doi:10.1002/2014WR016841.
Hussain, E., J. R. Elliott, V. Silva, M. Vilar-Vega & D. Kane (2020), Contrasting seismic risk for Santiago, Chile, from near-field and distant earthquake sources, Natural Hazards and Earth Systems Science, 20, 1533-1555, doi:10.5194/nhess-20-1533-2020.