Why are deep earthquakes uncommon beneath oceanic ridges?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

Deep earthquakes are uncommon beneath oceanic ridges primarily because of the high heat flow in the underlying mantle rock.1

While earthquakes are common at these divergent plate boundaries, they are restricted to the shallow crust where rocks are brittle and prone to fracturing as the crust rifts. In contrast, the intense heat present at these spreading centers prevents the buildup of the stresses required for deep-focus earthquakes, as the mantle material is too warm and plastic to behave in a brittle manner.12

Deep-focus earthquakes are instead characteristic of subduction zones, where cooler, rigid lithospheric plates descend into the Earth's interior.23