British Geophysical Association Postgraduate Research in Progress Meeting 2013

Five PhD students from the Geology and Geophysics research group presented their work at the annual British Geophysical Association Postgraduate Research in Progress Meeting, hosted by the University of Cambridge. Seismologists, Ryan Gallacher, Thomas Hall and Saikiran Tharimena, and exploration geophysicists Kelvin Amalokwu and Melis Cevatoglu presented a broad range of work from imaging deep earth structures and evolution of volcanic chains using earthquake seismic data, laboratory experiments to study elastic wave anisotropy to use of Carbon Capture and Storage of atmospheric CO2.

Understanding the processes generating the Cameroon Volcanic Line (CVL) was the basis of Ryan’s research work. This involved receiver function study of bulk crustal structure using earthquakes recorded by the Cameroon Broadband Seismic Experiment, together with results from a SkS shear wave splitting study of seismic anisotropy and local seismicity around Mt. Cameroon. The three methods indicate an absence of magmatic intrusion/partial melt in the crust with a vertical anisotropic fabric in the lithosphere.  These results suggest that hypotheses for the formation of the CVL should not include markedly elevated upper-mantle potential temperatures, or large volumes of melt production and intrusion, both of which can explain observations at hot spots and rifts worldwide.

On a deeper note, Saikiran’s research focussed on seismically imaging the Ontong-Java Plateau (OJP), the largest of the Large Igneous Provinces (LIP), using SS precursors to constrain the physical and chemical properties beneath OJP. The anomalous thick crust of OJP together with its low subsidence history, thermal stability and buoyancy has led to OJP being hypothesised to represent a modern day analogue for continental craton formation. Modelling the structure beneath OJP and understanding its evolution will provide a better insight into the mantle dynamics beneath OJP. A very distinct deeper, ~280 Km, velocity decrease was observed, which is believed to be the base of the seismic root of OJP. Various geodynamic models are being tested to explain the true nature of this discontinuity.

Laboratory experiments were conducted by Kelvin to study the elastic wave anisotropy in partially saturated fractured rocks. High global demand for natural gas has led to an increased focus on unconventional gas reservoirs such as tight gas and shale gas reservoirs both of which rely on fractures for fluid flow. Aligned fractures in rocks cause seismic anisotropy and can be detected using seismic methods. Elastic wave attenuation is more sensitive to the physical state of rocks than velocity, for example, changes in fluid saturation (eg. gas saturation) and the presence of fractures. As a result, understanding relationship between elastic wave attenuation and saturation in fractured rocks could be useful in identifying economic gas reserves (hydrocarbon & geothermal) in unconventional reservoirs.

Melis is looking at Carbon Capture and Storage (CCS), a promising technology, to deal with increasing atmospheric CO2 levels. To broaden its usage as a reliable climate mitigation option, understanding the fate of injected CO2 and its potential environmental impact in case of leakage is essential. To that aim, QICS project took place in Ardmucknish Bay, Oban in spring-summer 2012. CO2 was injected into unconsolidated shallow marine sediments over 36 days. High resolution seismic reflection data collected during pre-release and release stages of CO2 gave insights into CO2 related acoustic anomalies, as well as gas migration pattern within sediments. In addition, variation in the reflection coefficient and seismic attenuation emphasize CO2’s impact on physical properties of sediments.