It’s been a shaky start to the week for many lower North Islanders, with more than a dozen tremors being felt since Sunday’s magnitude 5.7 earthquake near Wellington.
The quake woke up many in the capital after it first hit at about 5.08am, 25km west of Wellington at a depth of about 30km. More than 37,000 people reported feeling the quake.
Just over 12 hours later at 11.20pm another quake hit, this time in Hawke’s Bay within 5km of Pōrangahau. The quake had a reported depth of 16km and was considered a “strong earthquake” by GeoNet.
Since then, a swarm of small earthquakes have been recorded in the region, creating unease for many residents.
Speaking to Breakfast this morning, GNS Science senior seismic advisor Jonathan Hanson said it was “very unlikely” the two shakes were connected.
“One of them is one of the earthquakes, the first one, the one that woke us all up down here in Wellington was at 5.00am and located out in the Cook Strait at kind of a moderate to shallow.
“The other main earthquake that happened on Sunday, up near Pōrangahau, happened at around 11.00pm and it’s kind of a much shallower process and a very different location.”
He explained that the smaller quakes felt around Hawke’s Bay were “typical” of the area’s seismic activity.
Hanson said the region had a subduction zone “just offshore”, which was when an oceanic plate runs into a continental plate and slides beneath it.
“What happens is we get a buildup of stress in that subduction zone, and it tends to get released in the Hawke’s Bay in the form of these kinds of sequences or swarms of activity.”
He said the other way stress is released is through “slow slip events”, where it is released much more gradually, and can last for weeks or even months.
Asked if the recent tremors were a sign that a much bigger earthquake was yet to come, Hanson said it was more “complicated than that”.
He explained that when stress is released in one area, it can create more stress on other parts of the same or nearby faults, but it can also release stress.
He said the far more common scenario was when a bigger event occurred, which is then followed by aftershocks that got smaller over time.
“Then much more rarely we do see bigger events that follow a sequence, so that’s when stress is kind of built up, but that is by far the least likely of those scenarios.”
Hanson gave some advice to any Kiwis feeling worried by the recent seismic activity. He said the best thing to do was to drop cover and hold, no matter where you are.
“So, if you’re in the toilet, you should actually still drop cover and hold. You’re in the shower, drop, cover, and hold. If you’re in a wheelchair, we call it lock your wheels in position and cover and hold.”
He also recommended anyone in an area at risk of tsunamis assess their situation and evacuate to higher ground if needed.