3. why do earthquakes occur at plate boundaries?

usually, the rock is moving along large cracks in earth's crust called faults. most earthquakes happen at or near the boundaries between earth's tectonic plates because that's where there is usually a large concentration of faults.movement along those faults can cause earthquakes too.

explanation:

answer: due to the convection current in mantle.

explanation: when the convection current occurs in mantle then, it impacts to the plate boundaries and mostly it's edges.