Poster of the New Zealand Earthquake of 16 August 2013 - Magnitude 6.5

Tectonic Summary

The M 6.5 August 16, 2013 earthquake south of Blenheim, New Zealand, occurred as the result of strike-slip faulting on or near the plate boundary between the Pacific and Australia plates. At the latitude of this event, the Pacific plate moves towards the WSW with respect to Australia at a rate of approximately 41 mm/yr. Preliminary faulting mechanisms for the earthquake in concert with the location and faulting mechanisms of the larger aftershocks suggest it is related to NE-SW right-lateral strike-slip motion, consistent with plate motion oriented displacements. This region of New Zealand has hosted a number of small-moderate sized earthquakes in recent weeks, including a M 6.5 earthquake approximately 40 km east of the August 16 event in the Cook Straight, on July 21, 2013. The July 21 event was preceded by several M 5.3-5.8 events and was followed by a dozen or more aftershocks between M 4.5-5.0, delineating shallow upper plate structures aligned NE-SW, and some deeper subduction-related activity, mostly offshore of the north coast of New Zealand's South Island. In contrast to the earlier events, the August 16 earthquake is on land, near the eastern end of the complex Marlborough Fault System. The event is located approximately 10 km southeast of the Awatere Fault in the vicinity of Lake Grassmere. The Marlborough Fault system is characterized by a series of NE striking right-lateral strike slip faults that have dismembered the northern South Island into a series of crustal blocks that are being transported to the northeast. Although there is no specific mapped surface fault that can be linked to the August 16 event at this time, the NE trending fault plane is similarly oriented to the Awatere and Clarence faults of the Marlborough system. In 1966 a M 5.8 earthquake (interpreted to have occurred offshore to the NE of the August 16 event) was widely felt in this area, causing surface deformation of the main railroad line in the region. That event is interpreted to have occurred on a blind structure sub-parallel to and southeast of the Awatere fault.

Earthquake Report

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