A 7.5-magnitude earthquake shook Hanmer Springs, north Canterbury, just after midnight this morning, and was felt across the country.
[Note: since this was written, the November 14 earthquake has been upgraded to magnitude 7.8.]
Aftershocks continue to rock the country – with a twenty over magnitude 4.5 – across the South and lower North Island, with many strong shocks in Wellington. Tsunami alerts for the east coast were issued shortly after the quake, with a focus on the Kaikoura coast. Civil Defence has since downgraded the tsunami warnings.
GNS Science said that the fault which caused the earthquake is currently unknown. But earlier this morning, John Townend – seismologist at Victoria University – told Radio New Zealand; “the seismologists at Geonet will be analysing all the seismic data to tease out the aftershocks to work out where they are, how big they are. That will give us a better understanding of exactly which fault produced this earthquake.”
The intensity of earthquakes is controlled by many factors: proximity to shaking, duration, and the frequency of waves being produced. Townend noted that “the earthquake that started it all was so big that the aftershocks will go on for some time…. [but] generally speaking, as time goes by, the rate of the aftershocks goes down.
The intensity and duration of the aftershocks can depend on structure of crust. According to seismologist John Risteau, who also spoke with Radio New Zealand, the crust in Canterbury is very thick and strong so it is able to build up a lot of stress. However, once it does rupture, it is very brittle – making aftershocks continue longer.
All recorded quakes are listed on Geonet, and for more information about the quakes, see below:
Geonet: M7.5 Kaikoura Quake: What we know so far
Stuff: Live chat with Geonet scientists
RadioNZ: Earthquake: Scores of aftershocks rattle country
RadioNZ: http://www.radionz.co.nz/news/national/318009/scientists-work-to-locate-fault-behind-quake
Herald: This is looking quite complex
Civil Defence: Tsunami threat following Hanmer Springs earthquake
Newshub: New Zealand earthquake: the worst-affected areas
RadioNZ: Kaikoura cut off by road
Live feeds:
Stuff: Live: 7.5 New Zealand quake causes casualties, tsunamis, and destruction
RadioNZ: Live 7.5 quake near Hamner rocks whole country
Herald: Live: 7.5 magnitude earthquake strikes near Hanmer Springs in South Island, tsunami warning for many New Zealand coastal areas
TVNZ: Earthquake LIVE: Key postpones overseas trip; Interlander may resume Cook Strait crossings today