The September 1, 2016 M 7.1 earthquake northeast of Gisborne, New Zealand occurred as the result of shallow oblique-normal faulting near the plate boundary between the Pacific and Australia plates. Preliminary focal mechanism solutions indicate oblique rupture occurred on either a steep dipping, southwest striking normal fault, or on a shallow dipping, north-northeast striking fault. The Pacific plate begins its westward subduction beneath the Australia plate at the Kermadec and Hikurangi trenches, 65 km to the east of this event, with a velocity of about 47 mm/yr. The depth, location and focal mechanism of the earthquake all indicate this is most likely an intraplate event within the subducting Pacific slab, rather than being an interplate thrust earthquake on the overlying subduction zone interface.
The Australia-Pacific plate boundary region east of the North Island of New Zealand has a history of large earthquakes both along the plate boundary proper, within the subducting Pacific Plate, and in the overlying Australia plate. Seismic activity is especially high in the Kermadec Islands region to the north. Within 250 km of the September 1, 2016 event, 28 other M 6 and larger earthquakes have occurred over the preceding century. The largest was a M 7.1 event in February 1995, about 45 km to the southwest of the September 1, 2016 earthquake. The 1995 event also occurred as a result of shallow oblique-normal faulting, and is not known to have caused any fatalities or damage. The 1995 M 7.1 earthquake was followed by a M 6.5 aftershock five days later.
The September 1, 2016 event was preceded by a M 5.8 foreshock, approximately 18 hours earlier and 30 km to the north, at a similar depth and with the same faulting mechanism as the subsequent M 7.1 earthquake.
- UTC: 2020-07-07 13:07
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