Shallow mantle seismic velocity structure at the East Pacific Rise between 8-10N (investigators Doug Toomey, David Jousselin, Robert Dunn, William Wilcock, Robert Detrick)

This data set is a tomographic model of P-wave seismic velocity structure at the East Pacific Rise between the Clipperton and Siqueiros fracture zones. The model was derived from active-source data acquired during the UNDERSHOOT seismic tomography experiment conducted during Ewing cruise EW9708 in 1997 (chief scientist Doug Toomey). The model and results are described in Toomey et al. (2007). Analysis and interpolation of two-dimensional crustal velocity profiles provided a 3-D starting model for the tomographic inversions in which off-axis crustal structure and thickness were constrained using crustal refractions and Moho reflections. Using a non-linear method for imaging heterogeneous and anisotropic structures, almost 5,000 Pn mantle refraction arrival times were analysed in the tomographic inversion. The data file is in ASCII format and contains longitude, latitude and velocity. It is masked by the derivative weight sum with values provided where there is data sampling and the results are for a region that is conformal to the seafloor and at approximately 9 km beneath the seafloor. The data set was generated as part of the project called Constraining Mantle Flow, Melt Supply, and Lower Crustal Structure Between the Clipperton and Siqueiros Fracture Zones from a Seismic Undershoot Experiment. Funding was provided by NSF awards OCE01-18597, OCE96-33264, OCE01-18383, OCE96-33814, OCE01-18450, OCE02-24903, OCE96-34132 and OCE01-17715.