Simplify the following text for a Grade 6 native English-speaking person.
Original: The 2011 Christchurch earthquake was a 6.3-magnitude earthquake that struck the Canterbury region in New Zealand 's South Island at on local time ( 23:51 UTC ) , causing widespread damage and multiple fatalities .
Simplified: The 2011 Christchurch earthquake was a 6.3 magnitude earthquake which struck the South Island of New Zealand at on NZT . ( This is 23:51 UTC ) .