No cells beneath continents. Tension at ridges, compression at trenches. Mechanism Top of convection cell is the oceanic lithosphere. Thermal boundary layer is the lithosphere. Ridge push from asthenospheric upwelling.
Slab pull at trenches, with denser phases deeper.
Better heat transfer from mantle. Compression at ridges, tension at trenches. Plate velocity is independent of plate area. Mantle drag suggests larger plates should be faster. Plates with more downgoing slabs move faster.