Figure F12. Estimated plate coupling length change since 20 Ma. The two horizontal lines represent the surface and Moho. Numbers are depths in kilometers. The thickened zone indicates a coupled zone. A. 20 Ma: steep subduction resembling the present subduction in the Marianas. B. 20-14 Ma: dip angle decreases. C. 10-6 Ma: subduction erosion proceeds. D. 6-4 Ma: stiffening of mantle wedge nose proceeds. E. 4-0 Ma: downdip end of coupled zone becomes shallower as hydration proceeds.

Figure F12. Estimated plate coupling length change since 20 Ma. The two horizontal lines represent the surface and Moho. Numbers are depths in kilometers. The thickened zone indicates a coupled zone. A. 20 Ma: steep subduction resembling the present subduction in the Marianas. B. 20-14 Ma: dip angle decreases. C. 10-6 Ma: subduction erosion proceeds. D. 6-4 Ma: stiffening of mantle wedge nose proceeds. E. 4-0 Ma: downdip end of coupled zone becomes shallower as hydration proceeds.