What are called slow-slip earthquakes – a phenomenon observed only in the last two decades - can last from days to years and produce up to tens of centimetres of displacements along faults. Specifically, they tended to happen within areas where the subduction zone was transitioning from being "stuck" beneath the southern North Island, to an area where the subduction zone was "creeping" further north, around Gisborne and Hawke's Bay. New Zealand slow-slip quakes play out in an area where the Hikurangi Subduction Zone is transitioning from being "stuck" beneath the southern North Island, to an area where the subduction zone is "creeping" further north, around Gisborne and Hawkes Bay. That was fluid stored deep within large mountains beneath the sea, and being fed down into the subduction zone, where it could prime the environment for slow-slip quakes. It was already generally thought fluids could play a role in modulating different types of earthquakes, and in this particular part of the subduction zone, scientists had happened to have documented many slow-slip events.

Source: New Zealand Herald July 07, 2021 16:52 UTC