New Zealand's South Island has been rocked by a significant earthquake – originally found to be of magnitude 6.4, but now revised down to 6.0. The epicentre – at a relatively shallow depth of 10 kilometres – has also been revised from its initial estimate of having been 35 kilometres north of Methaven to being 30 kilometres west of Arthur's Pass. This location puts the quake closer to the western coast. Monitoring stations recorded the seismic event at 6.48 am local time on Tuesday 6th January, and it has since been followed by more than 30 aftershocks – the largest of which reached a magnitude of 4.2. Despite the alarming size of the earthquake, its isolated location seems to have helped prevent damage or injury – although it was felt throughout both islands.
Speaking to The New Zealand Herald, resident Tony Foote described the sensation created by the earthquake.
"It rolled on a bit, quite heavily, and I felt a bit sea sick as my chair moved about. A bit like being on a rising and falling wave in a small boat. There was a worry it might be something bigger on the way, as an ornament I hung to see when quakes were happening swung 100mm side to side for several minutes, and the water in my cat's bowl moved up and down 20mm or so."
While the Alpine Fault is perhaps the better known of the many faultlines that underscore the breathtaking landscape of New Zealand, The New Zealand Herald reports that its involvement in this earthquake has been ruled out. The fault line that generated the event has yet to be identified, beyond the general location of the epicenter John Risteau – a seismologist with GNS Science (the leading provider of geoscience, Earth and isotope research in New Zealand) explained the precedence of today's quake, and its implications as a possible warning.
"We've had them [earthquakes in this area] in the past century – there have been at least a couple of others that have been above magnitude 6. Just be aware there could be a sizeable aftershock coming – but beyond that, we can't say for certain whether there'll be anything bigger coming."
With such a high level of seismic activity, the Alpine Fault offers a unique opportunity to develop a picture of changes and indicators that might aid in the development of an earthquake early warning system as project co-leader John Townend pointed out.
"The Alpine Fault appears to save up all its energy for one big showdown every few hundred years. In between big ruptures, it seems to stay locked and produce mostly minor earthquakes, but what controls this timing behaviour isn't clear."
[Image Via Twitter]