SEISM is an international multi-institutional project to investigate the crust and deeper mantle beneath the Seychelles. Our aim is to gain insights into mechanisms for continental breakup. Another is a better understanding of the transition from continental to oceanic setting in and around the Seychelles plateau. Such information will lead to a better understanding of volcanic processes and basin evolution in the region and maybe of value in hydrocarbon exploration in the Seychelles.

Despite being in the Indian Ocean the Seychelles islands are made of granite, more often associated with continental crust. Nearly 60 million years ago the Seychelles micro-continent was pulled from India during an episode of continental division. This division, or rifting continues today at a rate of a couple of centimetres per year. New material is being generated at the Carlsberg ridge which lies deep beneath the northern Indian Ocean between India and the Seychelles. This separation has resulted in not only remarkable geology and tectonic setting, but highly unique and diverse flora and fauna of the Seychelles. A mechanism for such micro-continent evolution is unclear, but recent work suggest that interaction between a continental margin and a mantle plume (a hot upwelling from deep in the Earth) may initiate a jump in location of a spreading centre, thereby isolating a chunk of continent.

Continental rifting is a key feature of the plate tectonic theory which has revolutionized our understanding of earth sciences in recent years. Large continental `plates' split up over time and move across the Earth's surface; oceanic material is created at mid-ocean ridges and destroyed at subduction zones (e.g. beneath Japan). The towering cliffs on the granite islands of the Seychelles were cited as evidence for continental drift some 40 years before the eventual acceptance of the idea of plate tectonics. Nevertheless, there has been little if any investigation of the structure of the Earth's mantle (depths deeper than ~20km) beneath the Seychelles micro-continent. Very slow (cm's per year) circulation in the mantle controls the motion of the plates and continents and shapes the surface of the Earth we live on. Seismology is ideally suited to imaging the deep Earth, employing techniques similar to those used in medical imaging (e.g., ultrasound).

The project has two separate components, an active source experiment and a passive source (earthquake) experiment. The first component investigated the Seychelles margin and its conjugate equivalent near the Laxmi ridge off the coast of India. The Darwin, a British research vessel acquired controlled-source seismic data in both areas during a period between late January and the middle of February 2003. The source was a low energy but finely tuned air gun array. The signal was recorded by sensors towed behind the ship, ocean bottom instruments and equipment located on various islands. Recorders on land were deployed on Mahe and the surrounding islands, the Praslin islands and Denis. The second component of the experiment is passive and longer in duration. Seismometers have been distributed on islands spanning a distance of nearly 500 km; Coetivy and Alphonse are the most southerly islands and Bird the most northerly. This experiment will last 12 months and involved the deployment of small portable seismic stations at 25 sites. Distant earthquakes (more than 3000 km away) will be used to image the deep Earth structure beneath the plateau. It is hoped that the seismic images will illuminate boundaries between oceanic and continental domains and show the structure of mantle convection beneath the micro continent.

The project is a collaboration between scientists from the Universities of London (Imperial College), Bristol, Leeds and Southampton and German scientists from the research institute in Potsdam. This experiment is made possible only by the support and help from various Seychellois agencies. An established scientific collaboration with the Seychelles National Oil Company has helped guide the scientific program. Collaboration with the Marine Park Authority (MPA) and the Seychelles Centre for Maritime Research and Technology (SCMRT) has also been crucial to the smooth running of the experiment. Logistical support for the deployments will come from the Island Development Corporation (IDC), the Seychelles Island Foundation, and the Ministry of Tourism. Finally, the co-operation from island managers (Denis, Bird, Cousine, Ile Aride, Coetivy) has been invaluable.