Since the big Kaikoura earthquake last week there have already been well over 5,000 aftershocks, all logged and recorded by GeoNet – the earthquake and volcano monitoring system that sends alerts to smartphones and is made available on the web.
So how does the movement of the earth's crust get recorded and then broadcast as an alert to your phone within seconds? To discover how the information moves from a fault line in the South Island to your digital device we headed out with some of the team from GeoNet.
'The speed of the network even amazes me sometimes. I was sitting at home last night feeling the 5.7 near Culverden as my phone was alerting me of the same earthquake, so it was being picked up by our recorders in the South Island, transmitted to our servers in Avalon [in the North Island]…. and was already being processed and initial estimates of the earthquake were being put out, as I was feeling the earthquake in Wellington' – Andrew Cowie, senior field technician, GeoNet
After the big quake, GeoNet was fielding up to 35,000 information requests per second, and got 233 million hits over the course of that first day. So how does the movement of the earth's crust get recorded, analysed, and then broadcast as an alert to your phone within a few seconds?
Well, as you might expect, technology plays a key role. A network of geophysical instruments transmit information about seismic movements using radio waves and cables to GNS Science's base in Lower Hutt where it is instantly analysed by an automated software application and then gets published automatically to the public. In fact, humans only really become involved in the process in the case of larger earthquakes (magnitude 4.5 and above) when a duty seismologist gets an alert, and has to examine the data.
To find out more about how the information moves from a fault line in the South Island to your digital device we headed out with Andrew Cowie a GNS Science senior field technician to Baring Head, a remote spot on the southern coast of the North Island. Baring Head is part of a network of more than 600 remote monitoring stations around New Zealand. It was here, at 12.02am on Monday 14 November, that data about the 7.8 magnitude earthquake started arriving from the Cape Campbell monitoring station located on the Marlborough coastline about 70 kilometres to the south.