Jamie Morton is the NZ Herald's science reporter.

Magnitude 5.0 aftershock hits near Kaikoura

The probability of another quake larger than 7.0 this month has been put at 21 per cent. Photo / NZTA/Facebook
The probability of another quake larger than 7.0 this month has been put at 21 per cent. Photo / NZTA/Facebook

The South Island has been hit by another aftershock, this time a 5.0 magnitude tremor.

It struck 25km southwest of Kaikoura at a depth of 26km at 7:52pm.

GeoNet reported today that the probability of another 7.0-plus quake striking has fallen further, but large aftershocks are still likely across a large area of New Zealand.

Read more: Unravelling the quake's quirks

The latest forecast issued by GeoNet put the probability of another quake over 7.0 occurring within the next 30 days at 21 per cent, compared with chances of 10 per cent this week and two per cent within the next 24 hours.

The probability of one or more quakes between 6.0 and 6.9 hitting had also decreased, but was still relatively high, at 90 per cent this month, 63 per cent this week and 16 per cent in the next day.

Smaller yet still significant aftershocks between 5.0 and 5.9 remained a virtual certainty, with probabilities of more than 99 per cent this week (an average 10 such-sized events) and this month (an average 24).

The probability of one or more in the next 24 hours was 85 per cent, with an average of 1.9 quakes.

GeoNet spokesperson Caroline Little said aftershocks were occurring throughout a broad area that surrounded the faults that ruptured in Monday's 7.8 earthquake.

"Most of these aftershocks are occurring near these faults, but a small number of aftershocks have occurred as far away as the lower North Island," she said.

"Our current forecasts indicate that it is likely for that aftershocks near these faults will continue, but for the frequency of aftershocks to decrease with time."

Source: GNS Science
Source: GNS Science

The area nearest the faults had a probability of 80 per cent or more for damaging shaking in the next 30 days.

In comparison, the probability of damaging shaking in the Wellington area was less than 10 per cent in that period.

"While this probability is considerably lower than in other regions, it is possible for shaking similar to what occurred on Monday to happen again in Wellington," she said.

The capital was already a high seismic risk area and Monday's earthquake had increased this risk, Little said.

Christchurch's aftershock probabilities were not greatly affected by the 7.8 earthquake.

The most likely scenario was that aftershocks would continue to decrease in frequency over the next 30 days.

The aftershock area. Source / GNS Science
The aftershock area. Source / GNS Science

Felt aftershocks would occur from the 7.8 epicentre near Culverden, right up along the Kaikoura coastline to the Cape Palliser and Wellington area.

Much less likely was the probability of a quake smaller than Monday's mainshock and between 7.0 to 7.8 - a 20 per cent chance over the next 30 days - and even more unlikely, with a probability of less than one per cent, was the possibility of one larger than the mainshock.

- NZ Herald

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