It's not entirely accurate to say that few earthquakes happen in the mantle. While most earthquakes occur in the Earth's crust, deep earthquakes do happen within the mantle, specifically in the subducting slabs of tectonic plates.

Here's why:

* Crust is brittle: The Earth's crust is relatively cold and rigid, making it prone to breaking and generating seismic waves when stress builds up.

* Mantle is ductile: The mantle, while solid, is under immense pressure and heat, making it more ductile (like taffy). This means it deforms slowly rather than breaking abruptly, leading to fewer earthquakes.

* Subduction zones: At subduction zones, where one tectonic plate slides beneath another, the descending slab (the subducted plate) is forced deeper into the mantle. This slab is still relatively cold and brittle, making it susceptible to fracturing and generating earthquakes at depths of up to 700 kilometers (435 miles).

Therefore, while earthquakes are rarer in the mantle compared to the crust, they do occur, particularly within subducting slabs. This is because the descending slab retains its brittle nature at depth, despite being in the mantle.