RESEARCH
In the Department, currently, some 40 academic and research staff and 44 research students are actively involved in research. The full range of our activities is best seen on the Department website. Here, for the newsletter, are a few snippets of what we are doing. Cindy Ebinger is heading up a major new project, EAGLE, based in Ethiopia, to investigate the transition between rifting and seafloor spreading. Mike Cottam tells about his experience at Syracuse University. Andrew Scott realises his dreams in China.
EAGLE Update
Cindy Ebinger
Project EAGLE (Ethiopia–Afar Geoscientific Lithosphere Experiment), a 3-year NERC funded project to study the crust and upper mantle beneath a continental rift in the transition between rifting and seafloor spreading, began in October 2001. The work is shared between Leeds, Leicester and RHUL in the UK, Addis Ababa University Science Faculty, the Geological Survey of Ethiopia, and Petroleum Promotion Unit . Although EAGLE funds are provided for seismic work, RHUL staff have raised additional funding to conduct field studies linking seismicity and faulting, and to ground truth upper crustal structure along the reflection/refraction profile of the rift zone (Leicester).
Project EAGLE is going well. Phase 1, which invloved deploying seismometers to record teleseismic earthquakes, started in autumn 2001 and is led by Graham Stuart from Leeds University. Phase 2, the Royal Holloway project, led by Cindy Ebinger, started in autumn 2002 and involved deploying 50 Guralp 6TD seismometers in an array over the rift valley to record local seismicity. In January, phase 3, the University of Leicester project led by Peter Maguire, shot two 400 km long wide-angle reflection lines along and across the Ethipian Rift. Twenty-two teams deployed 1,000 Texan geophones (about 1 every kilometre). In addition there were 150 6TDs recording. Seven teams fired 19 shots – 2 in lakes and 17 in boreholes, up to 2 tons in size, between 10 and 16 January.
The project has attracted quite a lot of media attention –newspapers, local TV and the BBC. So our Ethiopian colleagues definitely gained the publicity they desreved for hosting EAGLE, which is the largest ever seismic experiment in Africa.
Probe of Africa's break-up blasts
off
14 January 2003 – NewScientist.com news service
Natasha McDowell (NewScientist.com)
A remarkable seismic survey to probe how the African continent is splitting apart will collect its final data on Tuesday, when geophysicists set off their last controlled explosion. Since Saturday, over 70 scientists from Europe, the US and Ethiopia have detonated 19 explosions across and along Ethiopia's Rift Valley. Project EAGLE is Africa's largest ever seismic survey, and the world's biggest ever three-dimensional seismic survey.
Tectonic forces are in the process of slowly pulling the African plate apart. "It is the only place on Earth where molten rock bubbles to the surface and a continental split is actively taking place," says Peter Maguire, at Leicester University, UK, who is leading the study. A new ocean will form if, in several million years' time, the continent splits completely.
The seismic waves produced by the explosions will travel tens of kilometres down before being reflected back to the surface and detected by the 1000 instruments deployed. The data collected will help the geophysicists better understand better the roles that earthquakes and volcanic eruptions play in the fundamental tectonic transition from continent to ocean. However, the work will also bring benefits for one of Africa's most densely populated countries by mapping the seismic and volcanic hazards in the area. "The Rift Valley is the bread basket of Ethiopia, so a major earthquake or volcano would have a big effect," says Cindy Ebinger of Royal Holloway, University of London, also an EAGLE participant.
"When a continent is breaking apart, it does not just crack and go, but slowly stretches," says Ebinger. The strain is accommodated either by rocks sliding past one another, causing earthquakes, or by molten rocks welling up from deep underground to fill the opening space, ultimately leading to volcanic eruptions. In the transitional phase seen in the Rift Valley, "we do not know which of the two processes are more important," says Ebinger.
Monitoring the seismic waves generated by natural earthquakes has produced some data. But setting off controlled detonations of up to two tonnes of explosive is more informative because the exact time and place of the event is known. "We can therefore determine the velocities of the waves and so tell the difference between one rock and another and whether or not the rock is molten," says Ebinger. "Finding mainly molten rock beneath the Valley's floor would suggest magmatism is the dominant process in the transition." It would also suggest that the area is at high risk from volcanic eruptions.
The explosions have been detonated in two 400 kilometre long lines, one along the length of the Valley and the other across it. This gives 3D images which may help answer another fundamental question. Oceanic plates are generally made up of roughly 60-km long broken segments. "Break-up is a 3D process so we need 3D images to be able to ask whether segmentation starts before continental break-up or after," says Ebinger.
EAGLE is also gathering other geophysical data, including electrical conductivity measurements, which can detect rock type and magma.
"It's rare in geophysics for a single technique to give an authoritative answer," says Kathy Whaler, at Edinburgh University, Scotland, who is leaving for Ethiopia on Friday to take the conductivity measurements. "But putting together the data will enable us to test our models."
