Central Hawke’s Bay residents feel quake swarm

Damage in the fridge and office at The Duke, Porangahau, after April's earthquakes. Photo / Robert Houkamau

Thousands of people felt a swarm of earthquakes that began in southern Hawke’s Bay overnight last Thursday.

Starting Thursday evening a sequence of more than 27 earthquakes were detected near the coastal Hawke’s Bay town of Pōrangahau, including two Magnitude 4.8 (M4.8).

The first M4.8 earthquake occurred at 6.54pm on Thursday, June 8, with the second M4.8 occurring at 12am on Friday, June 9. A M3.0 shake was recorded off the coast of Pōrangahau on Tuesday at 11.24am.

Both of the M4.8 quakes were felt primarily around the Hawke’s Bay region, while the rest in the sequence have been smaller and not been felt by many. All the earthquakes were relatively shallow and occurred just off the coast.

GeoNet recorded the shaking as “strong” for both 4.8-magnitude events, however, most of the self-reports to the website were “weak” or “light”.

People up and down the North Island reported feeling the quakes, as well as some in the middle of the South Island.

Pōrangahau is located along the east coast of the North Island, where the Hikurangi Subduction Zone - the boundary between the Australian and Pacific Plates - drives much of the earthquake activity.

The sequence of earthquakes is similar to and likely related to a sequence recorded in April, which included a magnitude 5.9 earthquake within 5km of Pōrangahau that was closely followed by a M5.4 aftershock. The current earthquakes are offshore, further east than the April sequence, but both are consistent with the plate boundary subduction zone in the region.

The Pōrangahau region also experiences Slow Slip events (SSE) which are like earthquakes in slow motion, unfolding over weeks to months, and they cannot be felt by humans. There is active research to understand the relationship between seismicity and SSEs throughout the Hikurangi subduction zone.