13 Apr 2012

Sumatra quakes were aftershocks from 2004 - seismologist

10:01 am on 13 April 2012

Victoria University seismologist John Townend says Wednesday's earthquakes off the coast of northern Sumatra were very late aftershocks.

There have been at least 34 aftershocks, following the magnitude 8.6 quake, one of which was magnitude 8.2.

Mr Townend says 1300km of faultline was ruptured in the 2004 earthquake, which relieved a lot of tension but caused the plate beneath Indonesia to buckle in response.

Earthquakes in the past days are part of the response to that.

However, Mr Townend says the very late aftershocks do not have implications for Christchurch, which has had 18 months of aftershocks.

He said the Indonesian quake is in a completely different class and the aftershocks happening now are known as 'triggered' earthquakes, which occur as the techtonic plates re-position themselves.