Wellington City smart phone users made Saturday's shake a GeoNet record breaker

Monday, 27 January 2020

A record amount of reports to GeoNet following a magnitude 5.4 earthquake on Saturday night could be explained by the number of smartphone users in Wellington City, GNS says. 

By 1.12am the modest shake had generated 26,000 'felt it' reports on its website, eclipsing the 2016 magnitude 7.8 Kaikōura earthquake, which generated 15,840 reports.  

GNS science duty seismologist Elizabeth Abbott said the shake may have garnered such a response due to its proximity to densely-populated Wellington City. 

'The increase in smart phones is another factor with people able to easily submit a felt report via our website or using our GeoNet app.'  

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The late-night shock at 11.45pm on Saturday was a magnitude 5.4 earthquake, originating in Wellington Region's Kāpiti Coast, 45 kilometres north-west of Paraparaumu. 

It was 64km deep and caused 'moderate' shaking across the country.  

Abbott said deep earthquakes like the one on Saturday radiated outwards. The waves took a while to reach Earth's surface, causing it to be felt by more people. 

'An increase in depth can increase the length of time an earthquake is felt, and may feel like a longer, rolling quake.' 

Since the Kaikōura earthquake, people were more aware of the GeoNet tool, she said. 

'Each large earthquake we get in New Zealand increases awareness of GeoNet to more people, and we are receiving more felt reports.'  

The majority of reports centred around the lower North Island and Upper South Island, but some people reported feeling the shake as far afield as Northland and Canterbury.

The 'felt it' reports for the quake on Saturday were 10,000 more than that for the 2016 Kaikōura earthquake. 

Abbott said the numbers were not an exact indicator of how many people actually felt the earthquake. 

'There have been a number of large earthquakes that would have been felt by more New Zealanders than those reported on GeoNet.'  

'Felt it' reports help GNS to better estimate the intensity of the shaking, she said. It could also help them to better understand the extent of the shaking from future major earthquakes.  

'They are one way to gain insight in to how people experienced an earthquake and what that could mean for communities following an earthquake,' she said. 

'The 'felt it' tool is also useful for other agencies to estimate areas of potential damage, and where communities may need help.' 

NZ's most felt earthquakes 

Paraparaumu - Jan 2020 - 26,518 reports 

Kaikōura - Nov 2016 - 15,840 reports 

Taumarunui - Oct 2018 - 15,666

Porirua - Sept 2019 - 14,577 

Auckland - Mar 2013 - 15,433