2 Answers

The plates of the earth shift causing friction  you have an earthquake

Basically the tremors felt are the result to one of  earths tectonic plates moving against another.

The continents float on the earth molten core and for billions of years are in constant, but very slow, movement.

There are jammed together, mostly under the worlds oceans, where the crust is thinner because if the weight of the oceans.   When one breaks loose we have an earthquake and one slips below an ocean we get a tsunami, as happened in Japan that killed over 17,000 people

Others are on land, some of which can be seen, like those in Iceland that are currently rapidly melting the Glaciers there, that the global warming theorist would have us believe is caused by man.