Despite the devastating earthquakes in Christchurch and Kaikōura happening so close together, there is no evidence the frequency of earthquakes has changed. GNS measures about 15,000 earthquakes per year and of these 150 can be felt, about one every three days. However, because our recent large earthquakes have been close to major population centres, the impact has been greater.
This is a real issue. Fatalities resulting from earthquakes are predominantly caused by building failures and tsunamis. Globally there has been an increase in earthquake fatalities, not because of increased seismicity, but because of urbanisation. And the risk is growing.
By 2025 more than 5,500 million people will live in cities; more than the entire 1990 global rural and urban population. This puts an increased concentration of people in harm’s way – and is a huge expense in repairing critical infrastructure.
Earthquakes have cost Aotearoa close to $50 billion during the last decade, with the Government spending around $20 billion following Christchurch and $2 billion on Kaikōura.
The challenge for engineers is to ensure our infrastructure can withstand the impact of seismic activity, reducing the risk of fatalities and providing resiliency. Ultimately good design is the difference between earthquake survival and disaster.
And we’re doing it. Aotearoa is a world leader in seismic engineering because we’ve learnt from events and constantly seek to improve. Acknowledging that any loss of life is awful, we can also acknowledge improvements. The Christchurch and Napier earthquakes were similarly sized but Christchurch had a significant reduction in fatalities, something that can largely be attributed to the huge improvements in buildings’ seismic resistance. Where Napier’s fatalities occurred in multiple buildings, the tragic loss of life in Christchurch predominantly occurred in two buildings.
Christchurch taught us new lessons and, lest we become complacent, Mother Nature tested us with the Kaikōura earthquake and highlighted new vulnerabilities.