Final answer:
Earthquakes at continental-continental convergent boundaries are caused by plates smashing together with no subduction, leading to pressure build-up and mountain formation.
Step-by-step explanation:
During the process of mountain building at continental-continental convergent boundaries, the motion of the plates that causes earthquakes is best described by the following statement: 'The plates smash together with no subduction.' In these scenarios, there is a lot of pressure because the thick continental masses, being less dense and more buoyant, resist subduction, unlike the denser oceanic plates which can subduct more readily. Therefore, when two continental plates converge, they push against each other, leading to the formation of mountain ranges such as the Alps, through processes of buckling and folding of the Earth's crust. This intense pressure and stress build-up can lead to earthquakes along these boundaries.