Abstract
The 2016 MW7.8 Kaikōura earthquake ruptured a complex sequence of strike‐slip and reverse faults in New Zealand's northeastern South Island. In the months following the earthquake, time‐dependent inversions of Global Positioning System and interferometric synthetic aperture radar data reveal up to 0.5 m of afterslip on the subduction interface beneath the northern South Island underlying the crustal faults that ruptured in the earthquake. This is clear evidence that the far southern end of the Hikurangi subduction zone accommodates plate motion. The MW7.8 earthquake also triggered widespread slow slip over much of the subduction zone beneath the North Island. The triggered slow slip included immediate triggering of shallow (<15 km), short (2–3 weeks) slow slip events along much of the east coast, and deep (>30 km), long‐term (>1 year) slow slip beneath the southern North Island. The southern Hikurangi slow slip was likely triggered by large (0.5–1.0 MPa) static Coulomb stress increases.
Plain Language Summary
The 2016 MW7.8 Kaikōura earthquake ruptured a complex web of faults in New Zealand's northeastern South Island. In the months following the earthquake, Global Positioning System and satellite radar data reveal a few to tens of centimeters of rapid motion of the northern South Island and much of the eastern North Island, up to 600 km away from the earthquake. We interpret these displacements to involve up to half a meter of movement on the boundary where the Pacific Plate dives down (or subducts) beneath the northern South Island. The Kaikōura earthquake also triggered widespread slow slip events over much of the subduction zone beneath the North Island. Slow slip events are similar to earthquakes, as they involve rapid movement along plate boundary faults. However, unlike earthquakes that take seconds to occur, slow slip events take months to occur. This is arguably the clearest example ever of widespread, large‐scale triggering of slow slip events on a plate boundary up to a several hundreds of kilometers away from the earthquake that triggered them.
Key Points
Widespread afterslip and slow slip was triggered by the 2016 Kaikoura earthquake on Hikurangi subduction zone
Afterslip beneath northern South Island provides important constraints on the southern extent of Hikurangi subduction
Upper plate fault earthquakes at subduction zones influence timing of aseismic moment release on the megathrust, both regionally and locally