The M7.1 Īnangahua earthquake - 50 years ago today

Published: Thu May 24 2018 10:00 AM

On May 24th 1968 at 5:24 in the morning a magnitude 7.1 earthquake struck the West Coast of the South Island.

The M7.1 Īnangahua was destructive - with a depth of only 12km, there were huge impacts across Buller and substantial damage to Īnangahua, a community of around 300 people at the time. The earthquake was felt as far south as Otago and across almost all of the North Island.

This video of the aftermath of the earthquake, by GNS Science’s Simon Nathan who was a young geologist living in Westport at the time, captures how damaging the earthquake was.

There were many landslides and rockfalls across the steep terrain, one of which killed two people, and another which blocked the Buller River. Roads subsided and one person was killed when their car hit a damaged piece of road near a bridge. Buildings were damaged, some irreparably, particularly in Īnangahua. A pilot and two linesmen died when their helicopter crashed in the days after the earthquake.

Today the West Coast community are remembering the effects of the earthquake and we at GeoNet (who are obsessed with data and delivering it as accurately and timely as possible to New Zealand and internationally) are reflecting on how much progress we have made over the last 50 years in quickly determining what and where the impact of an earthquake is likely to be.

50 years ago, there was no automatic earthquake detection system (GeoNet is only 17 years old) so it took half a day before anyone knew where the epicentre was (the point on the earth's surface above where the earthquake starts). It took even longer to work out the earthquake’s magnitude. This video of Murray, who was reponsible for locating earthquakes in the 80's - is a nice explaination of how New Zealand's earthquake monitoring and locating system worked back then.

It’s hard to imagine the telecommunication landscape being so different to life as we know it today – no WiFi, no smart phones, no apps, no social media. On top of having very little communications with the outside world the damaged area had 15 aftershocks of magnitude 5 and above in the first month.

GeoNet’s network of instruments across New Zealand has grown to over 350 from 26 that were operating in 1968. This, along with improved telecommunications and computer processing, means we are much faster at locating earthquakes and monitoring other events, like volcanic activity.

To get rapid earthquake information to you our system automatically detects and reports them on our website and app. These earthquakes are then reviewed by our duty officers within 20 minutes to make sure they are accurate. Imagine if that still took half a day.

And we are still advancing this system further (like I said – obsessed).

Watch this space – we’ll keep you informed on our journey as we go.