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Structure of the Azores plateau from earthquake seismology


   Department of Earth and Environmental Sciences

   Applications accepted all year round  Self-Funded PhD Students Only

About the Project

The Azores Plateau is considered to have grown somewhat like Iceland, by excess volcanism at the Mid-Atlantic Ridge, and by volcanism continuing to historical times on the islands and in submarine areas around them. There are ample geochemical data indicating an anomalous source in the mantle beneath the plateau. Variations in thickness of the crust, representing total volume of melt from the mantle, are likely to reflect how these two sources have varied spatially and temporally. Although crustal thickness is known under the islands from seismological recordings, much less is known of crustal thickness and structure between the island stations, which is important for us to assess how the melt supply from the mantle has fluctuated.

Recordings of earthquakes with an array of five ocean bottom seismometers (OBSs) deployed in a NERC-funded project in 2020 have provided accurate locations and times of events up to magnitude Mb~4.0 for an area west of Faial Island. In this PhD project, those events will be identified in seismometer records from the islands, which is densely instrumented as part of efforts to identify seismic hazards to the population. The array of land-based records will be used effectively to carry out a giant seismic refraction experiment, allowing the resolution of key velocity interfaces, in particular the Moho. The structure would be compared with results of tomography and other methods applied to the land station data, as well as structure from gravity, geochemical modelling and mineral fluid inclusion studies.

The OBSs were deployed in response to an earthquake swarm at the western edge of Condor Seamount, an elongate volcano. The travel times to the land stations and assessment of potential shadow zones will be used to assess whether a melt body exists under the seamount and hence whether it poses a risk of future eruption. Evidence for other bodies underlying Faial and Pico islands can also be investigated.

The ideal candidate for this project would be a student with experience of geophysics and computing. It would involve collaborating with Dr Nuno Dias of the Instituto Politécnico de Lisboa, Lisbon, Portugal, who has studied data from an array of permanent and temporary seismometers installed on the islands. It will also involve working with Drs Ingo Grevemeyer and Dietrich Lange at the GEOMAR, Germany, who have identified many micro-earthquake events in the OBS data using algorithms based on artificial intelligence and have many years of experience in seismic refraction.

For enquiries please contact Dr Neil Mitchell,


Funding Notes

This is a self funded project for a September 22/23 start. Fee's for home students TBC (standard UKRI) for EU and International £25,500.

References

Dias, N.A., Matias, L., Lourenço, N., Madeira, J., Carrilho, F. and Gaspar, J.L., 2007. Crustal seismic velocity structure near Faial and Pico Islands (Azores), from local earthquake tomography. Tectonophys., 445: 301-317.
Dias, N.A., Téllez, J. and Matias, L., 2020. Insight on the crustal stress state in Faial and Pico Islands (Azores), from analysis of aftershocks of the 1998 earthquake. Pure Appl. Geophys., 177: 5169-5187.
Mitchell, N.C., Quartau, R. and Madeira, J., 2012. Assessing landslide movements in volcanic islands using near-shore marine geophysical data: south Pico island, Azores. Bull. Volcanol., 74: 483-496.
Mitchell, N.C., Stretch, R., Tempera, F. and Ligi, M., 2018. Volcanism in the Azores: A marine geophysical perspective. In: C. Beier and U. Küppers (Editors), Volcanoes of the Azores. Springer Publications, doi:10.1007/1978-1003-1642-32226-32226_32227.
Mitchell, N.C. and Stewart, I.C.F., 2018. The modest seismicity of the northern Red Sea rift. Geophys. J. Int., 214: 1507-1523.

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