Marlborough fault system

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.[3] The Kekerengu Fault and Jordan Thrust are closely associated with the Hope Fault.[7] It did not undergo significant rupture in the 2016 Kaikōura earthquake although there was minor motion on its seaward aspects, and some off fault uplift to its south except near the Northern Canterbury domain Conway-Charwell Fault which is parallel, and did rupture only a few hundreds of meters away.[5] After the main shock sequence there were aftershocks clustered to its south in the region of the Conway-Charwell Fault.[2]

The Clarence Fault runs from close to the Alpine Fault to about 10 km west of Ward, where it appears to terminate abruptly. A Holocene slip-rate of 3.5–5.0 mm/yr is estimated for this fault. At the surface the displacement appears to be nearly pure horizontal, but continuous uplift of the neighbouring Inner Kaikōura Range over the same period, suggests that some of the dip-slip component thought to be present at depth on the fault zone is transferred onto thrust or reverse faults under the range.[8] An extra 10° of clockwise rotation has been recognised within the block that lies northeast of the tip of the Clarence fault.[4] It takes its name from the Waiau Toa / Clarence River, which follows the fault trace in the northeastern section of the fault.

It is formed of two main segments; the Molesworth section to the southwest and the Eastern section to the northeast. The estimated recent slip-rate for the Molesworth section is 4.4 mm/yr.[9] It takes its name from the Awatere River whose valley follows the fault trace along some of its length.

The Wairau Fault is sometimes regarded as a direct continuation of the Alpine Fault and may be referred to as the Alpine-Wairau Fault. It takes its name from the Wairau River, which follows the fault trace for most of its length. It has an estimated slip-rate of 3–5 mm/yr.[10]

It is closely associated with the Hope Fault and Jordan Thrust at its south-easternmost edge and likely joins with the Clarence Fault to form the Wairarapa Fault offshore in Cook Strait.[7][11] Before joining with the Clarence Fault, The offshore segment of the Kekerengu Fault is known as the Needles Fault. In the 7.8 (M_w) 2016 Kaikōura earthquake[12] major rupture of both the Kekerengu Fault for 27 km (17 mi),[2] with maximum displacement 12.0 m (39.4 ft) ± 0.7 m (2 ft 4 in)[5] and the Needles Fault for 30 km (19 mi))[2] occurred.

The dextral[13] Elliott Fault branches from the central portion of the Clarence Fault and then rejoins it. The Acheron and Dillon sinsteral faults also connect these two faults.[13]

The Kelly Fault forms a major fork of the Hope Fault from just west of Harper Pass; it forks again to the west into the Newton and Hura faults just before connecting to the Alpine Fault.

The Jordan Thrust is a reverse fault that connects the southern end of the Kekerengu Fault to the Seaward Segment of the Hope Fault. It ruptured during the 7.8 (M_w) 2016 Kaikōura earthquake with a component of dextral-normal displacement in contrast to its long-term reverse motion.[5][2] This also resulted in major uplift to its coastal south east side as it approached the Papatea Fault.[5]

The dextral[13] Fidget Fault commences to the south of the Waiau Toa / Clarence River and runs along its valley initially before striking east to the south of the hill of Mackintosh Knob and intercepting the Jordan Thrust near the coast where the Jordan Thrust transitions to the Kekerengu Fault. Its eastern portion ruptured in the 2016 Kaikōura earthquake with some increased vertical displacement upwards to its north in the Seaward Kaikōura Range.[5] After the 2016 Kaikōura earthquake there was an aftershock cluster to its south.[2]

The Papatea Fault runs from the Jordan Thrust south east to Waipapa Bay where it historically was known to have a deep southeast plunge suggesting past dextral motion. In the 7.8 (M_w) 2016 Kaikōura earthquake it had a sinistral component however and aftershocks grouped along its length and towards Kaikōura.[2] The size of the displacements were marked and second only to those along the Kekerengu Fault in this earthquake. There was up to 7.3 m (24 ft) of left-lateral displacement and 9 m (30 ft) of west side up vertical slip.[5]

The Snowgrass Creek Fault was identified to be an active subsurface fault zone by optical displacement analysis (any surface rupture might be difficult to recognise due to mountainous location)[5] and was associated with a prominent group of aftershocks after 2016 Kaikoura earthquake.[2] It extends between the Kekerengu and Clarence faults northwest of Clarence. It trends northeast–southwest ( at about 210°) with displacement in this earthquake being mainly right lateral and it may lie within the hanging wall of a deeper fault structure.[5]

This is an active dextral fault between the Clarence and Awatere faults.[13] It had a 4.8 ± 1.2 m dextral displacement in the 1848 Marlborough earthquake of the Awatere Fault.[2]

This is an active dextral fault[13] that arises as a splay off the Alpine Fault south of where the Wairau Fault splays off, just south of the Blue Grey River and follows initially to the east its valley. The surface trace terminates to the east just beyond the Chimmney Stream before the Acheron River. There has been more recent upper crustal microseismicity in this fault than in the Clarence Fault to its south.[14]