Research Student 2013
Geophysics, Geodynamics and Tectonics
Research: Deep Earth Seismology
PhD: Transition zone structure beneath Iceland
My PhD research aims to investigate deep Earth structure beneath Iceland.
Seismic tomographic models observe a slow wave speed anomaly located beneath Iceland, which is generally interpreted as a region of higher temperature, causing the large amounts of volcanic activity observed in Iceland. The real question is how deep does this seismic anomaly extend? Does the anomaly exist only within the upper few hundred kilometres, or is it caused by a deep sourced mantle plume rising from the core-mantle boundary? Inherent problems with seismic tomography mean that narrow hot plumes are very difficult to observe at great depth, even if they are present.
The mantle transition zone from 410 to 660km depth separates the Earth's upper and lower mantle, defined by mineral phase transitions (olivine-to-spinel at 410km and spinel-to-perovskite at 660km). Discontinuities defined by these phase transitions can be observed using seismic data, and the inferred depth of the discontinuity varies laterally as a function of temperature and composition. Therefore, the depths of transition zone discontinuities beneath Iceland provide a way to investigate the depth extent and location of deep mantle temperature anomalies. In my research I use receiver functions generated from P-to-S wave conversions at discontinuities within the Earth, to investigate discontinuity depth variations across the Iceland region.
Receiver function analysis can also be used to investigate shallower features, revealing information on the structure of the Icelandic crust, and deeper structure, such has interesting midmantle signals suggestive of small scale chemical heterogeneity in the mantle. Both of these are research areas I am currently exploring.
Field Work: The University of Cambridge Icelandic Seismic Network
An important part of my work involves assisting in the running and maintenance of the University of Cambridge's large network of seismometers, which are deployed across Iceland, many of which are on loan from the government instrument pool SEIS-UK. A host of PhD students, technicians and professors regularly looking after these instruments, downloading the data they record, moving them to better locations, and fixing them when the sometimes extreme Icelandic weather takes it's toll.
These instruments are mainly used to record small magnitude local seismicity that happens in Iceland and is often linked to volcanoes and magma movement underground. However they can also record large magnitude distant earthquakes that happen on the other side of the world. These earthquakes travel deep within the earth through the mantle beneath Iceland. Careful analysis of the earthquake signal can give us information about the material they travel through. That's why these instruments and the data they record are so important for my research and for understanding what's going on deep beneath our feet.
Geophysics ; Seismology
Jenkins, J., Cottaar, S., White, R. S., and Deuss, A. (2016). Depressed mantle discontinuities beneath Iceland: Evidence of a garnet controlled 660 km discontinuity?, Earth and Planetary Science Letters 433, p.159-168