Wednesday, February 23, 2011

New Zealand Quake

A couple of days ago (February 21 at 23:51 UTC or February 22 at 12:51 pm NZDT), the city of Christchurch, on the South Island of New Zealand, experienced a large 6.3 magnitude earthquake.  It was particularly damaging because it was quite shallow at only 5 km of depth (by comparison, there was a 6.4 magnitude earthquake the same day south of the Fiji Islands at 562 km of depth!).  The official death toll at the moment is 76 but well over 200 people are missing and the death toll will certainly rise.  The images coming out of NZ are sad to see.

This latest earthquake is actually considered to be an aftershock from the September 3, 2010 magnitude 7.1 earthquake which struck near Darfield, NZ (35 km west of Christchurch).  Since this main quake, there have been a half-dozen earthquakes greater than magnitude 5 in the Christchurch region.

Why does New Zealand have large earthquakes?  Simple answer is that it lies on a tectonic plate boundary.

See New Zealand - east of Australia right on the boundary between the Pacific and Australian plates?  Here's a plot showing 10 years of shallow (depth < 40 km) earthquakes in New Zealand:

They're not uncommon!  The Pacific Plate is constantly pushing into and sliding under the Australian Plate deforming the island nation.  It's a fact of life that they're periodically get hit with big ones.  I could write more about convergent plate boundaries and such but it's late and I've been working since 8:00 am so I'll save it for another time.  I will leave with a neat image from Christchurch showing the power of earthquakes - a rail line deformed by the quake.  Steel tracks bent like taffy.

1 comment:

  1. Thanks, I've been looking around the internet for hours trying to find which plate movement was involved in the February 2011 Christchurch Earthquake, converge, diverge or transform. Found out from this the Pacific plate is constantly converging with the Australian plate.