What activity within the earth causes earthquakes?
Within the earth, radioactive atoms decay producing vast amounts of energy.
This heats up molten minerals in the mantle which then expand.They become less dense and rise towards the surface.Cooler material sinks to take their place.
Forces created by these convection currents move the tectonic plates slowly over the earth.
When the boundaries (edges) of the plates meet, huge stresses build up. These forces make the plates deform and mountains may be formed.
The plates may also suddenly slip past each other.
These movements cause earthquakes.
Scientists find it hard to predict when and where an earthquake will happen because we don't know when the tectonic plates will suddenly slip past each other.