Seafloor compliance will be measured at more than 50 sites on the axis and flanks of the East Pacific Rise between 9 20 north and 10 20 north. The melt distribution in the lower crust and uppermost mantle will be mapped. The primary scientific problems to be addressed include: How and why do morphological melt starved segments differ from robust segments ? Does melt pool at the crust-mantle boundary before percolating through the lower crust ? How does lower crustal melt decrease toward segment ends ?