During the earlier ages of a new world, earthquakes are frequent, and they are all characterized by great physical disturbances; especially is this true of the gas-contraction spheres, the worlds born of the immense nebular rings which are left behind in the wake of the early condensation and contraction of certain individual suns. 
The isthmus of Gibraltar, protecting the western basin of the Mediterranean, gave way as the result of an earthquake, quickly raising this inland lake to the level of the Atlantic Ocean.  Earthquakes are caused by sliding and shifting of the solid outer crust and not by volcanoes.  For millions upon millions of years earthquakes have diminished, but Urantia still has an average of fifteen daily. 
Andon and Fonta, the first parents of the human race, died in an earthquake.  Jesus was surprised when as a child he asked his father Joseph the cause of earthquakes and he did not know how to tell him.  Jesus advised his disciples not to worry about famines or earthquakes. 
See also: UB 59:3.6.