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.”
The earthquake is one of the strongest seismic events to hit the island since 2011, when an earthquake in Christchurch – on the South Island – caused widespread damage and 185 deaths. The extraordinary concentration of seismic activity in New Zealand is caused by its location along what is commonly referred to as the Ring of Fire. This series of tectonic plate boundaries runs through the Pacific Ocean and generates approximately 90 percent of the world’s earthquakes.
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.”
The development of an earthquake early warning system has long been an aim for seismologists, who are constantly striving for ways to effectively predict earthquakes in the hope of saving lives and protecting infrastructure. To that end, in October 2014, an international team comprising of scientific personnel from the U.K, Australia, the U.S, China, Germany and Canada began a project coordinated by GNS Science, Victoria University and the University of Otago. As reported by The International Business Times, the project team drilled a hole 1.3 kilometers deep into the heart of the Alpine Fault on the South Island of New Zealand. The fault – known as “The Earthquake Machine” – created the Southern Alps and is one of the most active seismic spots in the world.
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.”
Seismologists would be able to apply the understanding of this timing behavior to fault lines on a global scale – including whichever one is identified as having generated this most recent earthquake to shake New Zealand.
[Image Via Twitter]