Following global discovery of slow slip events at subduction zones in Japan, Mexico, and the United States, Aotearoa’s first slow slip earthquake (SSE) was detected offshore Gisborne in 2002. Scientists John Beavan and Laura Wallace found the SSE using one of the first continuous Global Navigation Satellite System (GNSS) instruments operated by GeoNet. 

Unlike typical quakes, SSEs unfold over weeks to months, shifting the plate boundary by the equivalent of a magnitude‑7 earthquake or more, releasing energy too slowly to be felt by humans or typical earthquake measuring devices (seismometers). Observations of SSEs continue to shape scientific understanding of how tectonic stress is stored and released on the Hikurangi subduction zone beneath New Zealand’s North Island.

Since 2002, significant investment has been made to expand permanent GeoNet GNSS instrumentation. Data from the network over the past 20 years has enabled scientists to reveal diverse slip behavior along the Hikurangi margin with smaller more frequent SSEs in the northern Hikurangi, and longer and less frequent SSEs to the south. 

The GeoNet network, Aotearoa’s unique subduction zone geometry, and passionate NZ scientists led by Laura Wallace helped encourage significant international science investment to deploying temporary seafloor networks and even borehole observatories to record SSEs. MBIE has also supported this work through the Tangaroa Reference Group enabling much of the offshore work to take place on board the RV Tangaroa .  

The data collected by GeoNet, and ongoing research partnerships with Japan, the US, and Germany keep New Zealand at the forefront of global SSE science and cultivates studies into how and where slip occurs, fault mechanics, the role of fluids in controlling slip timing and location, all ultimately feeding our long-term understanding of large earthquake and tsunami risks. You can keep an eye out for the next SSE on the GeoNet webpage.