Why are there so many earth quakes?

On my opinion , there are so many quakes because of so many unstable foundations on earth. If things that are bearing on these structures gets so heavy, naturally it will seek to move to a more stabler foundation /structure. Occurring calamities like volcanic eruptions, movement of the earth crust/plates are some causes of instablity. How I would wish to study natural science and learn more... Bye, and have a nice day.