Slow-slip earthquake in progress near Hawke’s Bay, New Zealand
A slow-slip earthquake (SSE) event has been occurring near New Zealand’s Hawke’s Bay, along the Hikurangi Subduction Zone since early December.
Image credit: Google, The Watchers
A slow-slip earthquake event is taking place in the Hikurangi Subduction Zone, a tectonic boundary between the Australian and Pacific plates. This zone runs along the east coast of New Zealand’s North Island and dips beneath the landmass, forming a complex and active geological system.
Global Navigation Satellite System (GNSS) stations near the Mahia Peninsula, located north of Hawke’s Bay, recorded land displacements of approximately 4 cm (1.6 inches) eastward and 1 cm (0.4 inches) southward, within the last 3 weeks of December.
Stations between Wairoa and Tolaga Bay exhibited similar movements with some sites moving up to 5 to 8 cm (2 to 3.1 inches). It represents up to 2 years’ worth of tectonic plate motion occurring in just 3 weeks.
The last recorded slow-slip earthquake in the area occurred in June 2023, showing the recurring nature of these phenomena in the Northern Hawke’s Bay and Mahia regions.
The ongoing SSE is a focus for international research. Since 2014, over 50 offshore instruments, including ocean-bottom seismometers and seafloor pressure sensors, have been deployed to study the subduction zone. The tools enable precise monitoring of tectonic movements and associated phenomena.
These sensors, part of an international collaboration involving researchers from New Zealand, Germany, Japan, and the U.S., aim to map the spatial extent of SSEs, detect associated seismicity, and refine knowledge of subduction processes.
The JOIDES Resolution drilling vessel, in 2023, installed 2 observatories up to 500 m (1 640 feet) beneath the seafloor, near the current SSE location. The observatories are designed to capture multi-year data cycles of slow-slip events.
A recent U.S.-funded project also installed seafloor flowmeters to measure sub-seafloor water movement related to SSEs. The instruments will be retrieved and analyzed for detailed insights into subduction zone processes.
In early 2024, an underwater remotely operated vehicle collected data from the observatories. This dataset will aid scientists in understanding the mechanics of SSEs and their relationship with regular earthquakes.
The Hikurangi Subduction Zone extends along New Zealand’s east coast. The fault is known for frequent slow-slip events which is distinct from regular earthquakes.
The Subduction Zone is the largest fault in New Zealand and experiences Pacific Plate movement at rates of 2 to 6 cm (0.8 to 2.4 inches) per year. SSEs were first detected here in 2002 after GeoNet deployed permanent GNSS stations along the coast.
SSEs involve gradual energy release over weeks or months without the ground shaking associated with conventional seismic activity.
SSEs relieve stress in some areas of a subduction zone but may increase stress in adjacent regions. The interaction can trigger smaller, shallow earthquakes. Multiple earthquakes between magnitudes 2 and 4 have already been recorded near the Mahia Peninsula, correlated with the current SSE.
SSEs are not unique to New Zealand but are prominent in its tectonic landscape.
They play the main role in accommodating tectonic plate motion and redistributing stress even though they occur too slowly to be felt.
References:
1 Hawke’s Bay slow slip wakes up – GNS – December 20, 2024
2 Slow slip earthquake occurring right now off the East Coast – East Coast Lab – Accessed on December 20, 2024
Rishika holds a Master’s in International Studies from Stella Maris College, Chennai, India, where she earned a gold medal, and an MCA from the University of Mysore, Karnataka, India. Previously, she served as a Research Assistant at the National Institute of Advanced Studies, Indian Institute of Science, Bengaluru, India. During her tenure, she contributed as a Junior Writer for Europe Monitor on the Global Politics website and as an Assistant Editor for The World This Week. Her work has also been published in The Hindu newspaper, showing her expertise in global affairs. Rishika is also a recipient of the Women Empowerment Award at the district level in Haryana, India, in 2022.
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