SNES: Codes For:Zelda III: Link To The PastZelda III: Link To The Past   

Location Of Third Magic: 
To get the elusive Quake Magic, first travel towards the waterfall region. On 
your travel there you will come across a ring of wooden posts. On the nearby 
shore there is a skull. Take the skull and throw it into the middle of the ring 
of posts. You will now be granted the Quake Magic. This will allow you to enter 
the Seventh Palace.