Not Mapped yet
While you're worrying about this, 90% of the earth's seabed has not been imaged EVER at any resolution.
Our best maps of the seabed ( http://topex.ucsd.edu/marine_topo/ ) come from mathematical inversions of satellite sea-surface altimetry data and assume density and physical properties of the rocks. They're OK as far as they go, but hopeless below 25 km spatial resolution and contain numerous glaring errors.
A mission to image the 70% of planet earth that is below the seas is not so sexy as a space mission, but IS important for scientific and commercial reasons...