Exploring the Earth's Subsurface

What's really happening beneath our feet? Physicists and Environmental Scientists at UEA are using ingenious methods to work out exactly what's flowing under the Earth's surface, helping us to better understand earthquakes, volcanoes and the complex engine at the heart of our planet. 

Dr Jessica Johnson, a geophysicist at UEA, is using physics to explore the processes which take place below the surface of the Earth, particularly the varying movements and pressures of fluids like gas, magma and water. As these fluids flow through underground channels, they can lead to the kind of geophysical hazards that devastate communities, including volcanic eruptions and large earthquakes.

The techniques that Dr Johnson has researched has helped create a clearer understanding of how this ‘subsurface fluid movement’ contributes to the generation of these destructive phenomena, giving us a better chance of monitoring, forecasting and mitigating them.

Johnson uses advanced technology, including supercomputers, satellites and sensitive motion sensors to study seismic activity and ground deformation at active sites. This research has taken her across the world to volcanoes in Hawai`i, New Zealand and Ecuador, where she works with teams of researchers to build accurate models of the volatile underground terrain. 

All rocks in the Earth’s crust have microscopic cracks and pores in them, which contain some sort of fluid (usually air or water). When rocks are put under stress, for example from a pressurising magma chamber in a volcano, some of the cracks and forced to close and some get opened. The open cracks tend to be aligned, causing earthquake waves to travel faster along the cracks than across them. This phenomenon is called seismic anisotropy. Johnson uses the signals from small earthquakes around active volcanoes to detect this anisotropy and so can determine what sorts of fluids are filling the cracks, and how pressurised the magma chambers are. One of the uses of this technique has been to detect increased sulphur dioxide emission from Kilauea Volcano in Hawai`i before a major eruption.

Since a complex interaction of various processes is responsible for natural disasters, future work for Johnson and her collaborators around the world will be to bring together multiple numerical models to generate ‘super models’ that synthesise different data streams into a unified picture. These models will be used to assess what might be happening in places that we can’t directly observe, and also to forecast future activity.

This pioneering work is deepening our understanding of these subterranean physical processes. This understanding is crucial to mitigating risk from natural hazards as the knowledge can be fed into monitoring efforts and disaster planning strategies. For example, Dr Johnson’s work has altered the way some volcano monitoring data in Hawaii is assessed and interpreted. 

Additionally, the fundamental physics that these models elucidate can be applied to other environments where subsurface fluid monitoring is important such as conventional, unconventional and renewable energy resources.

Dr Johnson’s work forms part of a huge range of ground-breaking research that takes place at UEA, working at the interface of Environmental Science and Physics. We want to understand all aspects of our global environment, from the land and oceans to the atmosphere and the Earth’s core.

Publications

Johnson, J. H., D. A. Swanson, D. C. Roman, M. P. Poland, and W. A. Thelen (2015), Crustal stress and structure at Kīlauea Volcano inferred from seismic anisotropy, chap 12 of Carey, R. J., V. Cayol, M. P. Poland, and D. Weis (eds.), Hawaiian Volcanoes: From Source to Surface, American Geophysical Union Monograph 208, pp 251–268, doi:10.1002/9781118872079.ch12.

Johnson, J. H. (2014). Seismic Anisotropy in Volcanic Regions. In M. Beer, I. A. Kougioumtzoglou, E. Patelli, & I. S.-K. Au (Eds.), Encyclopedia of Earthquake Engineering (pp. 1–16). Springer Berlin Heidelberg. doi:10.1007/978-3-642-36197-5_44-1

Johnson, J. H. and M. P. Poland (2013) Seismic detection of increased degassing prior to Kīlauea's 2008 summit explosion. Nat. Commun. 4:1668, doi:10.1038/ncomms2703

Johnson, J. H. and M. K. Savage (2012) Tracking volcanic and geothermal activity with shear wave splitting tomography. J. Volcanol. Geoth. Res., 223-224, 1–10, doi:10.1016/j.jvolgeores.2012.01.017