Seafloor Spreading and Subduction

Continental drift was largely ignored until the 1950s…

• When the USA started mapping the ocean floor properly, using new techniques

• Scientists such as Marie Tharp produced the first detail ocean floor maps

They discovered mountains and valleys they had not expected

This lead to the idea of seafloor spreading

• Scientists such as Harry Hess and Robert Dietz looked at the maps of the ocean floor and developed the idea of seafloor spreading.

Seafloor spreading

Evidence 4 – Magnetic Reversals

Sea-Floor Spreading

Discovery of Sea-Floor Spreading

Sediment thickness

Patterns of Earthquakes

Where does old crust go?

Earthquakes

Depths of earthquake foci

Where Does Ocean Crust Go?

Hugo Benioff, 1954

Benioff’s Interpretation Updated