Dougal B. Townsend

High-level stratigraphic scheme for New Zealand rocks

We formally introduce 14 new high-level stratigraphic names to augment existing names and to hierarchically organise all of New Zealands onland and offshore Cambrian–Holocene rocks and unconsolidated deposits. The two highest-level units are Austral Superprovince (new) and Zealandia Megasequence (new). These encompass all stratigraphic units of the countrys Cambrian–Early Cretaceous basement rocks and Late Cretaceous–Holocene cover rocks and sediments, respectively. Most high-level constituents of the Austral Superprovince are in current and common usage: Eastern and Western Provinces consist of 12 tectonostratigraphic terranes, 10 igneous suites, 5 batholiths and Haast Schist. Ferrar, Tarpaulin and Jaquiery suites (new) have been added to existing plutonic suites to describe all known compositional variation in the Tuhua Intrusives. Zealandia Megasequence consists of five predominantly sedimentary, partly unconformity-bounded units and one igneous unit. Momotu and Haerenga supergroups (new) comprise lowermost rift to passive margin (terrestrial to marine transgressive) rock units. Waka Supergroup (new) includes rocks related to maximum marine flooding linked to passive margin culmination in the east and onset of new tectonic subsidence in the west. Māui and Pākihi supergroups (new) comprise marine to terrestrial regressive rock and sediment units deposited during Neogene plate convergence. Rūaumoko Volcanic Region (new) is introduced to include all igneous rocks of the Zealandia Megasequence and contains the geochemically differentiated Whakaari, Horomaka and Te Raupua supersuites (new). Our new scheme, Litho2014, provides a complete, high-level stratigraphic classification for the continental crust of the New Zealand region.

The New Zealand Active Faults Database

ABSTRACT The New Zealand Active Faults Database (NZAFD) is a national geospatial database of active faults – including their locations, names and degrees of activity – that have deformed the ground surface of New Zealand within the last 125,000 years. The NZAFD is used for geological research, hazard modelling and infrastructure planning and is an underlying dataset for other nationally significant hazard applications such as the National Seismic Hazard Model. Recent refinements to the data structure have improved the accuracy of active fault locations and characteristics. A subset of active fault information from the NZAFD, generalised for portrayal and use at a scale of 1:250,000 (and referred to as NZAFD250), is freely available online and can be downloaded in several different formats to suit the needs of a range of users including scientists, governmental authorities and the general public. To achieve a uniform spatial scale of 1:250,000 a simplification of detailed fault locational data was required in some areas, while in other areas new mapping was necessary to provide a consistent level of coverage. Future improvements to the NZAFD will include the incorporation of data on active folds and offshore active faults.

Palinspastic reconstructions of southeastern Marlborough, New Zealand, for mid‐Cretaceous‐Eocene times

Abstract Southeastern Marlborough, New Zealand, preserves many complete sections through the Cretaceous/ Tertiary (K/T) boundary. Attempts to understand the paleogeography of these sections are hampered by the pervasive, Neogene deformation of the area associated with the propagation of the modern Pacific/Australian plate boundary through New Zealand. In this paper, we produce palinspastic maps of southeastern Marlborough for five intervals of Cretaceous and Paleogene time, based on a retro‐deformed, pre‐Neogene geographic model. Retro‐deformation takes account of: displacements on five major faults; distributed, between‐fault shortening; and a uniform, vertical axis, clockwise rotation of 100°. The mapped intervals are: (1) part of the Urutawan‐Motuan (middle‐late Albian, c. 105–102 Ma); (2) the Piripauan (latest Coniacian to late Santonian, 86.5–84.5 Ma); (3) the Early to early Late Haumurian (late Santonian‐Campanian, 84.5–72 Ma); (4) the late Late Haumurian to late Teurian (late Maastrichtian to late Paleocene, 68–58 Ma); and (5) the Waipawan‐Mangaorapan (early Eocene, 55–51 Ma). During the Cretaceous and Paleogene, southeastern Marlborough lay on the generally north‐facing, Pacific margin of proto‐New Zealand. The palinspastic maps record the progressive drowning of what we infer to be a faulted platform, the “Marlborough paleo‐platform”, that formed the eastern boundary of a large embayment, the “Marlborough paleo‐embayment”. In the late Early and early Late Cretaceous, terrigenous clastic sediments were deposited on the platform at mostly shelf to upper bathyal depths. Ngaterian (late Albian‐Cenomanian) and Piripauan (latest Coniacian to late Santonian) paleoshorelines lay within the study area and were oriented northeast‐southwest. Subsequently, regional, passive subsidence of the continental margin resulted in transgression towards the south and southeast and a switch from terrigenous clastic to biogenic sedimentation. By the end of the Cretaceous, much of the Marlborough paleo‐platform was at outer shelf to bathyal depths; by the early Eocene, it lay entirely at bathyal depths. During the latest Cretaceous and Paleogene, the position of the Marlborough paleo‐embayment coincided approximately with a significant boundary in sedimentary regime, separating dominantly biogenic sediments in the east from mixed biogenic‐siliciclastic sediments to the west. The palinspastic maps show internal consistencies that give us some confidence in the new analysis. Differences from previous maps are attributed both to the retro‐deformation and also to variations in the locations, values, and number of data points used to construct isopachs. Locally restoring paleogeography by retro‐deforming structures is likely to be of most use where the amount of deformation is high (e.g., >20% shortening and/or some tens of kilometres of fault displacements), where the isopachs are well constrained by robust data points, and where regional or global controls on sedimentary and biological patterns are significant and of interest.

Map of the 2010 Greendale Fault surface rupture, Canterbury, New Zealand: application to land use planning

Abstract Rupture of the Greendale Fault during the 4 September 2010, M W7.1 Darfield (Canterbury) earthquake produced a zone of ground-surface rupture that severely damaged several houses, buildings and lifelines. Immediately after the earthquake, surface rupture features were mapped in the field and from digital terrain models developed from airborne Light Detection and Ranging (lidar) data. To enable rebuild decisions to be made and for future land use planning, a fault avoidance zone was defined for the Greendale Fault following the Ministry for the Environment guidelines on ‘Planning for the Development of Land on or Close to Active Faults’. We present here the most detailed map to date of the fault trace and describe how this was used to define and characterise the fault avoidance zone for land use planning purposes.

Palaeoearthquake histories across a normal fault system in the southwest Taranaki Peninsula, New Zealand

Abstract The tectonic origin, palaeoearthquake histories and slip rates during the last c. 26 ka have been examined for six normal faults (referred to here as the Rahotu, Oaonui, Kina, Ihaia, Kiri and Pihama faults) within the Taranaki Rift, New Zealand. A minimum of 13 ground-surface rupturing palaeoearthquakes have been recognised on four of the faults using analysis of displaced late Quaternary stratigraphy and landforms. These data, in combination with 21 new radiocarbon dates, constrain the timing, slip and magnitude of each earthquake. The faults have low throw rates (c. 0.1–0.8 mm a–1) and appear to be buried near the Mt Taranaki volcanic cone. Recurrence intervals between earthquakes on individual faults typically range from 3–10 ka (average c. 6 ka), with single event displacements ranging from c. 0.3–1.5 m (average c. 0.7 m) and corresponding moment magnitudes incorporating estimated fault rupture areas of Mw 6.1–6.6. Recurrence intervals and single event displacements typically vary by up to a factor of three on individual faults, with only the Oaonui Fault providing any evidence for near-characteristic slip (of about 0.5 m) during successive earthquakes. The timing and slip of earthquakes on individual faults appears to have been interdependent, with each event decreasing the likelihood of additional earthquakes across the system.

Strike-slip ground-surface rupture (Greendale Fault) associated with the 4 September 2010 Darfield earthquake, Canterbury, New Zealand

Abstract This paper provides a photographic tour of the ground-surface rupture features of the Greendale Fault, formed during the 4 September 2010 Darfield earthquake. The fault, previously unknown, produced at least 29.5 km of strike-slip surface deformation of right-lateral (dextral) sense. Deformation, spread over a zone between 30 and 300 m wide, consisted mostly of horizontal flexure with subsidiary discrete shears, the latter only prominent where overall displacement across the zone exceeded about 1.5 m. A remarkable feature of this event was its location in an intensively farmed landscape, where a multitude of straight markers, such as fences, roads and ditches, allowed precise measurements of offsets, and permitted well-defined limits to be placed on the length and widths of the surface rupture deformation.

Post c. 300 year rupture of the Ohariu Fault in Ohariu Valley, New Zealand

Abstract An important component of quantifying seismic hazard and risk in regions such as Wellington is to characterise both the long-term rate of occurrence of the regions major earthquake-generating active faults, as well as potential interactions between faults (e.g., the potential for earthquake triggering). This paper describes paleoseismic data from two trenches (Ohariu Valley) and a natural streambank exposure (Horokiri valley) c. 24 km apart, which constrain the timing and size of recent surface rupture events on the northeast striking Ohariu Fault c. 6 km northwest of Wellington City. One event is recorded at all three sites and radiocarbon age constraints indicate it correlates with the 1050–1000 cal. years BP event previously identified elsewhere along the fault. A younger, smaller (decimetre-scale) event is recorded in one of the Ohariu Valley trenches, and the timing is constrained by two radiocarbon ages to post-310 cal. years BP. This event may either be a small, primary Ohariu Fault rupture, or a triggered event associated with a large earthquake on a nearby fault. If it is a triggered rupture, then a possible mechanism is dynamic triggering associated with one of the recent large-great earthquakes on the Wellington (post-300 yr), Wairarapa (AD1855), or Awatere (AD1848) Faults. Small rupture events do not necessarily contribute to the recurrence interval classification of the Ministry for the Environment Active Fault Guidelines, but they could be important for sensitive structures crossing the fault and for lifelines crossing multiple active faults.

Surface Rupture of Multiple Crustal Faults in the 2016 Mw 7.8 Kaikōura, New Zealand, Earthquake

Multiple (>20 >20 ) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M w Mw 7.8 Kaikōura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M G w MwG ) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was ∼12  m ∼12  m on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7–1.5 m south of the Hope fault, and 5.5–6.4 m to the north. M G w MwG using two different methods are M G w MwG 7.7 +0.3 −0.2 7.7−0.2+0.3 and the seismic moment is 33%–67% of geophysical datasets. However, these are minimum values and a best estimate M G w MwG incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M G w MwG 7.8±0.2 7.8±0.2 , suggests ≤32% ≤32% of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the Kaikōura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the Kaikōura earthquake is ≥5,000–10,000  yrs ≥5,000–10,000  yrs , and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries.

Earthquake history at the eastern boundary of the South Taupo Volcanic Zone, New Zealand

ABSTRACT At the eastern boundary of the south Taupo Rift, the NE-striking, rift-bounding Rangipo and the ENE-striking Wahianoa active normal faults intersect. We investigate their intersection at the Upper Waikato Stream to understand the kinematics of a rift termination in an active volcanic area. The Upper Waikato Stream Fault is a previously unrecognised seismogenic source also at the eastern boundary, capable of producing a MW6.5 and up to MW7.1 earthquake if it ruptures in conjunction with the Rangipo or Wahianoa faults. We found a minimum of 12 surface-rupturing earthquakes in the last 45.16 ka on the Upper Waikato Stream Fault (mean slip-rate c. 0.5 mm/yr), and a minimum of nine surface-rupturing earthquakes in the last 133 ka on the Wahianoa Fault (mean slip-rate c. 0.2 mm/yr). Periods of highest slip-rate on these faults may coincide in time with Taupo, Ruapehu or Tongariro eruptions, but, despite their intersection, movement was not coincident across all faults. The Upper Waikato Stream Fault responded to a major Taupo Volcano eruption, the Wahianoa to a major eruptive sequence from Mt Tongariro and the Rangipo to major explosive events from Mt Ruapehu.

Crustal extension in the Tongariro graben, New Zealand: Insights into volcano-tectonic interactions and active deformation in a young continental rift

Figure DR1. Waihi Fault main field outcrops. A-D Field outcrop ‘Tong 78’ showing displaced tephra mainly from the Ngauruhoe Formation (Moebis et al., 2011) cut by fault 5. E-F Field point outcrop ‘Tong 70’ showing displaced tephra mainly from the Bullot Formation from Mt. Ruapehu (Donoghue & Neall, 2001; Pardo et al., 2012) cut by fault 6. See Table DR6 for more information about the stratigraphy.