Original: The 2011 TÅ hoku earthquake and tsunami was caused by a 9.0-magnitude undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST ( 05:46 UTC ) on Friday , 11 March 2011 .
Simplified: The 2011 TÅ hoku earthquake and tsunami was an 9.0-magnitude earthquake followed by tsunami waves .