How do subduction zones initiate, develop and end: Imaging the Reversal of Subduction in the Solomon Islands

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Plate tectonics is a fundamental theory for explaining earthquakes, volcanoes, crustal deformation and therefore the motion at the Earth's surface. However very little is known about how destructive plate boundaries initiate, evolve and end. This is central to plate tectonics, as it is thought that the dominant driving force of plate motions is the gravitational pull of subducting plates.
In the Solomon Islands and Papua New Guinea, the Pacific and Australian plates are converging. In the north one subduction zone is nearing the end of its life cycle as anomalously buoyant oceanic plate is stalling subduction. To the south in the San Cristobal Trench, a new subduction zone has initiated in response to continued convergence of the Pacific and Australian plates, making this the perfect place to understand subduction initiation and cessation.

In this urgency proposal we will deploy seismometers for 1 year to record aftershocks from sequence of 4 major earthquakes with magnitudes between 7.1-7.6. These recordings and other recordings of earthquakes from around the globe will allow us to delineate with high accuracy the plate interfaces of the new and old subducting slabs and image the slab structures at depth. The structure of the old and new subduction zones will illuminate the processes occurring at depth which are shifting the force balance in the region to reverse the sense of subduction.
The proposed experiment will be enhanced by concurrent studies scheduled to be deployed in Fall of 2014, which includes a multimillion pound ocean bottom seismic deployment by colleagues in Japan. The combined array will allow us to image the Pacific plate which is stalling the subduction, allowing us to investigate what conditions are necessary for a plate to halt the descent of the slab into the mantle. Thus we will be able to understand how subduction stops and starts.

Planned Impact

This research will have direct societal impact for seismic and tsumami hazards particularly with the local people and governments of Papua New Guinea and the Solomon Islands. In addition, subduction of large igneous provinces has been suggested as a major means of concentrating economic deposits in the resulting volcanic arcs. We will be working with local and regional governments for siting our seismic instruments as well as national government authorities charged with hazard assessment and mining rights. We have three research expeditions planned to the region for the seismic deployments, service runs and recovery legs. During each of these trips we will give presentations to local and national authorities and to inform them of our research goals, findings and make suggestions for further work. We will also engage with them at regular intervals for planning and logistical purposes.

Publications

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Armitage J (2015) Upper mantle temperature and the onset of extension and break-up in Afar, Africa in Earth and Planetary Science Letters

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Marcuson R (2014) Seismic anisotropy predicted for 2-D plate-driven flow in the Lau back-arc basin in Physics of the Earth and Planetary Interiors

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Tharimena S (2016) Seismic imaging of a mid-lithospheric discontinuity beneath Ontong Java Plateau in Earth and Planetary Science Letters