Earth and Planetary Science : Geophysical Research
Geophysics forms a major theme-based grouping within the Subsurface Research area. A variety of field, laboratory, analytical, numerical and computational methods are used to determine the structure and elucidate the dynamics of the Earth and other planets at a range of scales. Academic staff contribute to teaching the undergraduate geophysics degree, and many to the geology and environmental geoscience streams. A regular series of research seminars provides a focus for the use of quantitative mathematics and physics for the study of the Earth.
: Earthquake Seismology
: Glacial Geophysics
: Physical Geodesy
: Rock Magnetism
: Rock Physics
: Marine Geophysics
Industrial Imaging & Modelling of the Earth's Subsurface : Andrew Curtis
University of Edinburgh scientists develop new ways to create clearer seismic images of the Earth's subsurface. Mathematics and Physics are key disciplines used to optimise the design of surveys, and to simulate and analyse recorded wavefields in order to extract subsurface information. Using interferometry, we also use background 'noise' in the Earth to image the subsurface. Knowledge of geology and rock physics then guides the construction of static models of current subsurface geology, and dynamic models of its geological evolution.
Edinburgh Seismic Research - ESR - is the UK's largest group of academic scientists in Exploration Geophysics. It spans all parts of the exploration seismology processing and interpretation chain, and provides a world-class, one-stop shop for expertise and research in interrogation, exploration and monitoring of the Earth's subsurface.
We develop and test new methods in our state-of-theart seismic processing lab. Results from joint industrial projects are transferred directly to partners' R&D under tried and tested modes of collaboration. These include sponsored research projects, Ph.D. studentships, Knowledge Transfer Partnerships, and industry scientists may pursue research under the Industrial Hosting Program.
On going work also includes:
Surface waves provide key information about the lithospheric structure of the Earth. They are dominantly sensitive to shear velocity variations down to sub-lithospheric depths, and hence are a good data source for exploring regions of anomalously high or low velocities, or for mapping variations in crustal thickness (since the base of the seismological crust is in part defined by a large jump in shear velocity with depth). The technique used is called tomography, and involves applying inverse theory to infer the velocity structure given data about the surface wave group or phase velocities.
We have applied these methods to explore beneath the Tibetan Plateau and surrounding regions using inter-earthquake surface wave phase velocities, to map the velocity structure beneath the Eurasian continent, and our current work is devoted to producing global crustal thickness and average crustal shear velocity maps.
A key feature of almost all current earthquake tomography is that the inverse theory applied is linearised. This means that the relationships between the (surface wave) data that we measure, and the Earth model that we wish to estimate, are approximated by a linear function. This is an approximation, and particularly for geophysical problems which are all nonlinear in reality, it can be a very poor approximation causing bias and error in the Earth models
found. As a result, all estimates of uncertainty in Earth models given to-date are likely to be in significant error.
For the first time ever, we have produced a global tomographic model of the crust that employs no linearised methods. The inverse theory used is fully nonlinear (it involves using neural networks to embody the full, nonlinear relationships) and produces full probability distributions that describe the uncertainty in the result of the inversion. This is a paradigm shift in the field of seismology as it shows that nonlinear methods can be made
sufficiently efficient to be applied on to large scale problems (against popular opinion!)
Some published work:
- Tomography under Tibet and Eurasia using surface waves (Curtis and Woodhouse, 1997; Curtis et al., 1998; Devilee et al., 1999; Curtis and Snieder, 2002)
- Application of neural networks to invert surface wave velocities for Moho depth (crustal thickness) and other sub-surface discontinuities (Devilee et al., 1999; current work with Ueli Meier and Jeannot Trampert)
- Modelling and inverting for crustal deformation associated with large earthquakes (Curtis and England, 1997)
Geophysical Exploration of Lake Ellsworth
The geophysical survey of Lake Ellsworth has recently been funded by the Natural Environment Research Council's Antarctic Funding Initiative.
The NERC geophysical survey will involve a 2-year campaign, which will comprise ground-based radio-echo sounding (to reveal the lake surface extent, the ice thickness over the lake and the subglacial morphology of the lake's locale), seismic sounding (to determine the lake's bathymetry and, possibly, the thickness and structure of lake-floor sediments), and a series of surface measurements to reveal surface accumulation and strain rates.
In the first season (probably in 2007-8), the seismic and RES surveys will be conducted. The second season is simply to resurvey GPS stations and accumulation instruments (to reveal ice flow and surface accumulation).
The term complex system formally refers to a system of many parts which are coupled in a nonlinear fashion.
When there are many non-linearities in a system (many components), behaviour can be highly unpredictable.
Complex systems research studies such behaviour.
Complex systems research overlaps substantially with nonlinear dynamics research, but complex systems specifically consist of a large number of mutually interacting dynamical parts.
In general, complex behaviour cannot be predicted by considering one elementary component of the system. The behaviour is emergent. For example, sine wave pulses of car velocities in traffic jams or the Gutenberg-Richter Law.
Processes controlling carbonate deposition and erosion are complex, yet are important if we wish to be able to predict properties and geometries of fossilized carbonate strata observed in nature. This ability is particularly important in situations where pores in carbonate rocks hold extensive reservoirs of fluids. For example, more than 60% of the remaining recoverable world-wide reserves of hydrocarbons are held within carbonate reservoirs; the ability to predict the lateral variability in rock properties
in these reservoirs greatly affects the efficiency with which the hydrocarbons can be extracted from the ground.
Modelling complexity in carbonates
. Proceedings of Mathematical Geology (doc)
Research themes include all aspects of the Earth's gravity field, including (i) physical geodesy, geoid computation and the theory of height systems; applications to oceanography; (ii) very high precision absolute and relative gravity measurement, with applications to recent crustal movements and engineering geology; (iii) compilation and analysis of regional and satellite based global gravity databases with applications to isostasy, deep Earth and regional geological structure, including applications to ther planets; (iv) theoretical studies of potential field transfromation and spectral analysis.
Geomagnetic Earth Observation from Space (GEOSPACE)
GEOSPACE is a new NERC 5 year Consortium Grant exploiting data from the new generation of vector magnetic field satellites. Our scientific aims are to unravel and model the various sources contributing to the measured magnetic field and its time variation to a much higher degree of accuracy than previous achieved. This involves studying external magnetic fields in the magnetosphere and ionosphere, the internal fields they induce in the crust and mantle, the static field locked in lithospheric rocks, magnetic fields generated by ocean tides (owing to motional induction in electrically conducting seawater), and the field generated by dynamo action in the liquid outer core.
The GEOSPACE group is seeking applications for a vacancy at the postdoctoral level
The Electrical Resistivity Structure of the Crust Beneath the Northern Main Ethiopian Rift
Magnetotelluric surveys measure the variations of the natural electromagnetic field on the Earth's surface. The induced part of the electromagnetic field provides information on the distribution of the electrical resistivity to a depth of a few kilometres. The method is passive and capable of revealing previously hidden structures that are invisible to traditional seismic techniques. MT surveys have successfully been used to image beneath basalt deposits on the Isle of Skye and Lake Tana in Ethiopia.
The Tana basin is covered with extensive Eocene-Oligocene continental flood basalts which mask underlying formations. The MT survey confirmed the existence of a Mesozoic sedimentary basin between lava flows and the Precambrian basement. The MT data assists exploration companies target activity more precisely at potential hydro carbon deposits, minimising risk and significantly reducing project costs.
2D model of the resistivity structure across the main Ethiopian rift, from an inversion of both the TE and TM mode data on a finite difference grid. The Adama basin terminates to the SE against the Arboye rift border fault.
We are interested in fundamental magnetisation processes of natural magnetic minerals in order to assess the reliability and fidelity of the magnetic information contained in rocks. For this purpose we are using both micromagnetic calculations run on high-performance computers as well as experimental techniques to characterise synthetic and natural magnetic minerals and their behaviour.
In the figure below, you see a model of two arrays of 3x3 magnetite cubes with identical properties and edge length of approximately 200nm, the only difference being the spacing of individual cubes. The coloured arrows mark the magnetic microstructure of these magnetite cubes. As you can see, only a slight change in cube spacing changes the magnetic microstructure dramatically. With such micromagnetic models, we can explain magnetisation processes in natural rocks.
Picture taken from: Evans, M. E., Krasa, D., Williams, W., Winklhofer, M., Magnetostatic interactions in a natural magnetite/ulvöspinel system, submitted to Journal of Geophysical research.
We study rock deformation, fluid flow, tracer transport, and fluid-rock interactions under stress in the brittle field. We specialise in coupled physico-chemical processes, particularly their time-dependence. We use a variety of experimental, analytical, and numerical techniques to elucidate the fundamental processes at work, or to characterise constitutive rules that can be input into larger-scale models. Our unique equipment pool has recently allowed us to produce realistic deformation bands in the laboratory, and to investigate primary diagenesis in carbonate and sandstone samples.
Other areas of research :