Final answer:
Clay intensifies the effects of earthquakes and can trigger landslides due to its water-absorbing, expanding properties, which weaken it. Earthquakes are caused by the sudden release of stress along plate boundaries, as predicted by the theory of plate tectonics.
Step-by-step explanation:
One sub-surface material which intensifies the process of earthquakes and mass movement is B) clay. Clay can absorb water and expand, which reduces its strength and increases its susceptibility to movement. When an earthquake occurs, these properties can lead to more significant ground displacement and can trigger landslides.
Earthquakes are a natural phenomenon related to the theory of plate tectonics. The Earth's crust is broken into various plates that float on the semi-fluid asthenosphere beneath them. These plates move, and when they interact at plate boundaries, they can cause intense geological activity, including earthquakes. Earthquakes happen when the stress on rock at plate boundaries overcomes the friction holding them together, causing sudden release of energy and seismic waves that shake the ground.