Series of quakes from unmapped fault
A magnitude 3.3 earthquake off the coast of Timaru on Tuesday morning was the fifth to hit the area this month.
Between February 1 and 19, five quakes struck off the coast of Timaru.
They ranged in magnitude from 2.2 to 3.3 and struck at depths of 8km to 16km, about 5km to 15km east or northeast of Timaru. All five earthquakes were classed as weak by GeoNet.
GNS Science seismologist Dr John Ristau said the ‘‘swarm’’ of quakes came from an unmapped fault.
‘‘Small earthquakes such as these typically will not occur on active faults, but rather rupture their own small bit of crust that happens to be weak.’’
Timaru’s surrounding area was typically a site of ‘‘low seismic activity’’ with only 13 earthquakes recorded since January 1, 2018 – eight of those hitting this year, Ristau said.
The sudden influx was ‘‘likely due to stress building up in an area that isn’t capable of releasing it in one larger earthquake’’.
The quakes did not suggest there was anything bigger coming.
‘‘Earthquakes can happen anywhere in New Zealand, even in places where quake activity is normally low,’’ Ristau said.
‘‘It does serve as a good reminder that no matter where you are, it makes sense to be prepared for the possibility of an earthquake.’’
James Thompson, team leader for Canterbury’s Civil Defence and Emergency Management branch, said the offshore fault did not have the potential to trigger tsunami.
But quakes off the west coast of South America might, Thompson said.
‘‘The only relief with that is we get 15 hours’ notice.’’
He said ‘‘little swarms’’ of quakes were expected two to three times a year around New Zealand.