The following animation shows all earthquakes located by GeoNet between the time of the M7.8 mainshock (large red dot, November 13 2016, 11:02:56UTC) and November 18 2016:
The majority of the aftershock zone is about 200km long, almost entirely to the northeast of the M7.8 mainshock. Aftershocks extend down to 50km and more, with a dense cluster of shallow (yellow and green) seismicity at the northeastern limit of the main aftershock zone.
To put this seismicity in context, the following animation shows all earthquakes with magnitude greater than 4.0 located by GeoNet between 2000 and November 18 2016:
Here one can clearly see the deeper subduction zones defined by their seismicity (magenta) under the northern and southernmost parts of New Zealand. Between these two subduction zones, the right-lateral, strike-slip, Alpine fault forms the main plate boundary (shallow, yellow and green seismicity near the west coast of South Island).
The November 2016 earthquake (large red dot) and aftershocks occur near the southern termination of the northern subduction zone.
The M7.2, 3 September 2010 UTC Canterbury / Darfield earthquake, the M6.2, 21 February 2011 UTC Christchurch earthquake and their aftershocks show up as a shallow seismicity (green and yellow) about 150km to the southwest of the 2016 earthquakes:
We acknowledge the New Zealand GeoNet project and its sponsors EQC, GNS Science and LINZ, for providing data used in this study.
Visualization / animation: SeismicityViewer