Figure 7.

(a) Velocity gradient plot for the standard model. The high gradient contour of 0.5 s⁻¹ is marked by black thick dashed curve, defining the Layer 2/3 boundary, which approximately corresponds to the base of the crustal turning rays Pg. (b) Crustal thickness (green) and Layer 2 (red), Layer 3(blue) thicknesses. The Layer 2/3 thickness values at the ridge‐axis (∼75 km) are anomalous due to the low velocities and are not considered in the discussion. The dashed lines are polynomial fits. The edges of the model with less ray coverage are not shown. See the text for discussion.