What Could Have Caused the Quakes in South America, New Zealand, and Italy?

It was October 27 when a terrifying quake hit Italy. This was the second event that followed another deadly quake earlier this year. Then, the world was surprised when an earthquake hit Christchurch in New Zealand, sending people to alarm when it was estimated to be followed by a tsunami. Just hours after the quake in New Zealand, another very strong tremor was felt in South America. The question in everyone's minds is: what could have caused these tremors? And the most important of all is, are they all related?