This large collaborative project involves researchers from Wash U., LDEO, U. Hawaii, SIO  and LDEO. The Eastern Lau Spreading center (ELSC) is a back arc spreading center lying close by the Tonga trench. Fluids expelled from the subducting slab cause melting of the upper mantle above the slab, producing the volcanos of the Tonga Ridge, and strongly influencing the structure of the southern ELSC. The ELSC seismic experiment will use two large deployments of ocean bottom seismometers to image the oceanic crust near the spreading center and the structures connecting the ELSC to the down going slab.

1. 1)The “passive” component of the experiment will use the abundant earthquakes in the down going slab recorded by 55 ocean bottom seismometers (OBS) during a year long deployment starting in Nov. 2009 to image the structure in the upper mantle. I will be working with my colleague Bill Menke, and with students and postdocs (TBD) and our collaborators on various components of this large data set. We will be using measurements of seismic anisotropy and seismic tomography to investigate structure and mantle flow beneath the spreading center. The OBS array data will also be used to locate the abundant seismicity expected in the shallow crust near the spreading center to investigate the tectonics and hydrothermal systems of the ridge. The OBSs for this component of the experiment will be deployed in November 2009 using the R/V Revelle and recovered one year later using the R/V Kilo Moana.                                                                                        
   

2. 2)The “active source” component of the experiment was conducted during early 2009  by Columbia’s ship the R/V Langseth.  Seismic arrivals from pneumatic sound sources were recorded by a large number of OBSs to image in glorious detail the structure of the crust and uppermost mantle beneath the spreading center.