Gurnis 9417645 The time has come to more fully understand the flow and rheology of slabs from initial descent of the oceanic lithosphere as it slides by the over-riding plate down through its complex passage into the mantle transition zone. This will require that a new generation of dynamic models be simultaneously tested against both observations at intermediate scales (10-100 km) and at larger scales (100-100000km). This lime of research has been made possible by recent incorporation of faults between subducted and over-riding plates in dynamic slab models. When faults are incorporated between plates, oceanic trenches naturally arise and the essential trends of all relevant observations are reproducible. ****
