Extending the Lau Imaging Experiment to Study the Deep Tonga Seismic Zone

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In this project, researchers will install an array of 8 land broadband seismographs in Fiji for one year to complement an array of 55 ocean bottom seismographs that is already funded by NSF-Ocean Sciences for different objectives. The additional stations will expand the aperture of the seismic deployment to encompass the Tonga deep seismic zone, which contains ~ 66 % of the worlds deep earthquakes, allowing optimal raypath coverage for study of deep earthquakes and imaging mantle processes associated with the interaction of the slab and the transition zone.Slab processes at depths of 200-700 km, including deep earthquakes, mineralogical phase changes, and volatile transport and release into the surrounding mantle, are of great importance for understanding the dynamics of the earth. The goals of the study include placing constraints on the mechanism of deep earthquakes by mapping the configuration and studying the characteristics of individual faults in the Tonga deep slab. They will use high precision earthquake relocation methods for this task. They will study systematic patterns in deep earthquake rupture parameters in the subduction zone to see if they fit with global trends. They will place constraints on termperature and composition analmalies in the mantle wedge above the slab using seismic tomography, and using receiver functions, they will study the implications of reflectors in the mantle wedge.The researchers and students supported by this work will assemble a unique high density combined land-sea dataset from broadband seismographs immediately over the most prolific deep seismic zone in the world. They will also be working closely with seismologists from the Fiji Mineral Resources, thus facilitating scientific exchange and the training of younger scientists from a 3rd world country.