Here's why:
* Mid-ocean ridges are areas of divergent plate boundaries. This means the tectonic plates are pulling apart, creating space for magma to rise from the mantle.
* The asthenosphere is a partially molten layer within the upper mantle. The heat from the rising magma melts the rock in the asthenosphere, making it less dense and causing it to rise.
* This upward movement of hot, less dense asthenosphere brings it closer to the surface at mid-ocean ridges.
Therefore, the top of the asthenosphere is found at a shallower depth beneath mid-ocean ridges compared to other areas of the Earth's surface.
