Marlborough Fault System

The Marlborough Fault System is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island, New Zealand, which transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary of the Kermadec Trench, and together form the boundary between the Australian and Pacific Plates.

The Marlborough Fault System consists of four main dominantly strike-slip fault strands, which together carry almost all of the displacement associated with the plate boundary. Other smaller faults form as splays of these main faults or accommodate deformation of the crust between them, such as the Newton and Hura Faults at the western end of the Hope Fault and the Jordan Thrust that formed the Seaward Kaikoura Range. The dextral strike-slip across this zone has also involved clockwise rotation of the intervening fault blocks of about 20° since the early Pliocene.

The Marlborough Fault System formed at about 5 Ma, during the early Pliocene, in response to a change in plate motions. The new plate vector was significantly oblique to the Alpine Fault, causing an increased amount of convergence. The set of strike-slip faults formed to accommodate this change by taking up most of the strike-slip component.

There are four main fault strands, although many other smaller faults, of either strike-slip or thrust type are known.

The Hope Fault forms the southernmost part of the Marlborough Fault System. The estimated slip-rate during the Holocene is 20–25 mm/yr, just over half of the plate boundary displacement. At its northeastern end it links into the Jordan Thrust and most of the displacement is transferred onto that structure. It takes its name from the Hope River, which runs along one of the central fault segments. The Kekerengu Fault and Jordan Thrust are closely associated with the Hope Fault.

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