- Department of Earth and Ocean Sciences, University of Liverpool, U.K.
Dr Susan Cole
“SKS shear-wave splitting analyses beneath Germany and the Mediterranean and its implications for tectonic evolution.”
Purpose/Aims and Results:
Seismic anisotropy gives us a method to study the motions, and deformations, within the mantle due to its relationship with the preferred orientations of minerals, such as the highly anisotropic olivine. As seismic waves will travel through an anisotropic medium at different velocities, depending on their propagation direction and the fast axis direction of the anisotropic medium, analyses of the waves recorded at a receiver can indicate the orientations and structures of the ordered mediums. In the upper mantle, an ordered medium could be the result of the finite strain on minerals, due to deformation and drag forces caused by the motion of the plates above. Hence, seismic anisotropy is an important method of modelling mantle influences in orogenic formations and lithosphere-asthenosphere coupling.
My study analysed data from events recorded between 1992 and 2001 in the German Regional Seismic Network (GRSN), the Czech Regional Network (CZRN), and the Mediterranean Network (MEDNET). The results at each station were modelled as the data showed a more complicated structure to the anisotropy than can be explained by a single, horizontal layer; instead, it was thought that at least two layers would be necessary to produce the results because of the variation in the splitting parameters with backazimuth. The results of the modelling suggest a more complicated structure than a [relatively] simple two layer model across the entire region, and may be due to lateral changes in the thickness of the lithosphere. A possible structure may be a profile of the lithosphere which thins much faster to the south of the Alps than towards the north.
The anisotropy was most likely formed by the complex and dynamic history of the Eurasian, African, and Adrian plates, and their interaction with one another. The results found in this study are unable to be explained by models of excessive dilatancy, fault-parallel fast axis directions or drag flow anisotropy from extension and plate motions. Fossil anisotropy may account for a small proportion of the whole anisotropy seen, but would be constrained to a depth within the lithosphere; the main contribution to the anisotropy must come from depths within the asthenosphere. Plate motion-related shear flow appears to be the most likely model for the presence of the majority of the anisotropy.
“Understanding the internal dynamics of lahars with geophysical techniques”
- To develop new methods and techniques which will be adapted to test hypotheses derived from past studies.
- To characterise changes in a flow channel using scales from a few square metres up to 50km leading to new dynamical models for mass flows
- Collect data, pre- and post-event, to calibrate simulations
- Use digital topographic data to make quantitative assessment of sediment volumes eroded / deposited in order to derive functions for predicting lahar erosion / sedimentation in any catchment
The methods used to determine and develop the above will include:
- Remote Sensing
- Load cell-pressure transducers
- Clast marking
- Passive magnetic induction
- Overbank deposit traps
- Numerical modelling calibration, testing and development
- Observation and sampling programme
- Standard sedimentology methods will also be used to interpret the deposits
Research will be carried out at Mt Ruapehu, New Zealand, and Mt Semeru, Indonesia. Possible other sites include Mt Pinatubo, Philippines.
Commonwealth Scholarship 2006-2008
Funding for research from Marsden Grant…