Praneeta Mahajan
Hamilton, April 27, 2023
Residents across Hawke’s Bay experienced strong shakes after part of the region was struck by a severe magnitude 5.9 earthquake on Wednesday, 26 April 2023, during the late morning hours, following by dozens more aftershocks.
The first earthquake struck at a depth of 21km near the rural area of Pōrangahau in Central Hawke’s Bay at 10.16am, followed by a magnitude 5.4 earthquake at a depth of 17km a few minutes later in the same location. This was followed again by two smaller quakes of magnitude 3.9 and a magnitude 3.5, with more than 25 smaller earthquakes reported in the hour after the first earthquake was reported.
Seismologists warned the aftershocks could continue for days, even months, to come in the region already hard hit by Cyclone Gabrielle. The National Emergency Management Agency confirmed there was no tsunami threat triggered by the earthquakes.
Hawke’s Bay Civil Defence Emergency Management Group controller Ian Macdonald said that the residents could return following an earlier message that if the shaking was “long or strong” they should self-evacuate.
What the scientists say
Hawke’s Bay is one of the most seismically active regions in New Zealand.
Dr Katie Jacobs, duty seismologist at GNS Science, said the earthquake and many aftershocks had been felt “strongly and widely” across the North Island, with GeoNet receiving more than 20,000 felt reports.
“This is an area that does experience frequent earthquake activity, and this number of aftershocks is typical for events of this magnitude,” she said, adding more shaking could be expected in the coming weeks to months but decreasing over time.
“Pōrangahau is located along the Hikurangi Subduction Zone which drives much of the earthquake activity along the East Coast of the North Island. The region also experiences slow slip events – which are earthquakes that happen very slowly (and are not felt), with energy that is released over weeks to months.”
Dr Jacobs said they had not received any reports of landslides related to this event, but they can happen as a result of earthquakes, with homes near hills or steep slopes most at risk.
Central Hawke’s Bay Mayor Alex Walker said her main concern was the coastal community of Pōrangahau, which was “already battling” to recover from the impacts of Cyclone Gabrielle.
She said, “The main road out to the community is still accessible post-cyclone but several feeder roads and had been badly damaged, particularly by large slips. Land movement is definitely of concern, especially as it had been raining quite heavily across the district over the past few days.”
While an especially isolated area, its residents were resilient, Mayor Walker said. She thanked residents who evacuated for being prepared and urged the community to remain alert.
Recent Updates
GeoNet has recorded 27 aftershocks in the hours of darkness after yesterday’s “severe” magnitude 5.9 earthquake near Pōrangahau.
From 6pm Wednesday, 26 April 2023 to 8am Thursday, 27 april 2023, aftershocks ranged from magnitude 2.1 to magnitude 4.2. The average depth of the shakes stayed around 14km. They were all predominantly located within 5km of Pōrangahau, in a similar area where the original quakes struck.
GeoNet classed most of them as “weak” and “light”, with two at 6.01pm and 8.54pm reaching the “moderate” threshold (4.2 and 3.9 magnitude respectively).
Praneeta Mahajan is an Indian Newslink reporter based in Hamilton.
