Curiosity got me to download NZ earthquake data from the GNS Science webpage.
My graphic shows clearly that there was a relatively quiet period in September
at the time that GNS said on the 14th Sep– “Canterbury could get at least two more aftershocks of magnitude 5.0 or higher, but the risk of a bigger earthquake is fading by the hour, GNS Science says.”
They also said – “Gerstenberger said the aftershock figures had been updated daily, and it had been a ‘textbook’ sequence”.
Then further in the article – “GNS spokesman John Callan said there was now only a remote chance of a magnitude 6.0 aftershock.” With the benefit of hindsight – I wonder if GNS told authorities that their mid Sept optimism had failed to pan out – and that by late January there had been four aftershocks over magnitude 5.
I have to say I do not like the 23 Feb statement on the Geonet webpage – where they say “…slow decrease in general activity had made it less likely.”
Also on Radio Australia on the 23rd Feb GNS are saying that all the activity is aftershocks re Darfield.
The frequency of shocks had gone down but the data shows the persistence of several magnitude 5 shocks post September.
I am saying that the data can be looked at this way:
[1] The Darfield earthquake aftershocks were mostly over by late September.
[2] Then by October a new event had commenced – an earthquake swarm with activity more dispersed in time – with 3 shocks of magnitude 5.1 in October – the mag 4.5 & 4.9 at Christmas – then the 5.1 in January – in the next four weeks there was only 5 shocks between 4 to 4.5 magnitude.
[3] Then the terrible surprise of Lyttelton.
Our knowledge of this new seismic zone is so short – there may yet be twists and turns on the road ahead.
Useful earthquake animation map.
If you want to help victims with a donation – The Salvation Army has an appeal site – specify Christchurch earthquake appeal
