Slow-slip event in progress under the Kāpiti-Horowhenua area, New Zealand
Image credit: GNS/GeoNet
A slow-slip event began under the Kāpiti-Horowhenua area, New Zealand in mid-September 2021, and is expected to continue for several more months.
The part of the subducting Pacific Plate 30 – 50 km (18 – 31 miles) beneath Kāpiti has started moving slowly again after 5 years of being ‘stuck’ to the overlying Australian Plate, GeoNet reports.1
The Hikurangi subduction zone – the boundary between the Australian and Pacific Plates – extends along the east coast and dives underneath New Zealand's North Island.
"We frequently have slow-slip events on the shallower part of the subduction zone off the east coast, but this time, it’s the deeper part under Kāpiti that is slowly slipping," said GNS Science Geophysicist Laura Wallace.
"This slow-slip event began in mid-September under the Kāpiti-Horowhenua area and is expected to continue for several more months, as has been the pattern in this region in the past.
"We have recorded about 6 cm (2.3 inches) of movement on the plate boundary so far," Wallace added.
Model showing the amount of movement on the Hikurangi subduction zone since mid-September this year, in centimeters. The arrows show displacement of GeoNet continuous GPS sites used to detect the slow-motion earthquake. Image credit: GNS/Geonet
Slow-slip events are common in New Zealand.
The country sees shorter events more frequently offshore the east coast, but these Kāpiti events typically only happen every five years or so and tend to last about a year. The last time a slow-slip event occurred in this area was after the 2016 Kaikōura earthquake.
"Slow-slip events can involve the same amount of movement on the plate boundary as a magnitude 7 earthquake, only they occur so slowly that no one would know. They can also produce some local felt earthquakes, although we haven’t observed any noticeable ones yet that we’d associate with this event," Wallace said.
Reference:
1 Kāpiti slow-slip event now underway – GeoNet
Teo Blašković founded The Watchers in 2011 and edited it until 2026, covering seismic and volcanic activity, extreme weather, space weather and near-Earth objects. Articles on this page are his archive.
Published in the last 24 hours
- Forecasters say this winter’s El Niño could reach historic strength, but the last one that big, nicknamed Godzilla in 2015–16, left Los Angeles with about two-thirds of its normal rain while storms pounded the Pacific Northwest Epicenter
- Winds circling the North Pole have slowed sharply this month, the same kind of disruption that in January 2019 split the polar vortex and sent Chicago to minus 23°F, cold enough that rail crews ran flames along the tracks Epicenter
- In April 2014, golden-winged warblers in the mountains of Tennessee, songbirds weighing about as much as four dimes, fled their breeding grounds a day or two before a tornado outbreak and flew hundreds of miles south, while the scientists tracking them sheltered in a Waffle House Epicenter
- After record Nordic heatwave, Swedish researchers to recreate indoor heat to study older adults Epicenter
