Risk of second big quake decreases

GeoNet has revised their Kaikoura quake aftershock forecasts, downgrading the risk of another large earthquake.

They now put the odds of another earthquake between magnitude-6 and magnitude-6.9 hitting within 30 days at 15 per cent, down from 18 per cent in February.

The chances of another quake at magnitude-7 or higher is down in the next 30 days is down to 1 per cent from 2 per cent in February.

‘‘We like this downward movement in our forecast; it is good step in the right direction,’’ GeoNet scientists wrote in their release.

‘‘But does this mean we don’t need to worry about more big earthquakes? No, absolutely not. Another big earthquake is still well within the probabilities in our models. A 15 per cent chance in a month is still a concerning probability.

‘‘We need to continue to be prepared for earthquakes as these will go on for years to come. The ongoing Canterbury Earthquake Sequence is an example of aftershocks that can last for years after the initial mainshock.’’

Since the magnitude-7.8 earthquake in November 14,796 quakes have been recorded by GeoNet. Four of them were at magnitude-6 or greater, with 56 between magnitude-5 and magnitude-5.9.

On a wider timeframe, the chance of large aftershocks is higher. There is a 10 per cent chance another magnitude-7 or larger aftershock will hit in the next year, and a 68 per cent chance one between magnitude-6 and magnitude-6.9 will occur.

The aftershocks from the Kaikoura earthquake would mostly affect the immediate area surrounding Kaikoura.

The probability of an aftershock that causes internal building damage and strong shaking within the next year are as high as 20 per cent in Kaikoura. They are at just 3 per cent in Wellington.

The Alpine Fault still has a 30 per cent chance of rupturing in the next 50 years.