Delia Strong

Petlab: New Zealand’s national rock catalogue and geoanalytical database

ABSTRACT The Petlab database is New Zealand’s online national rock and analytical database, and provides an accessible, structured and permanent data repository for the local and global geoscience communities. The database contains locations, descriptions and analyses of rock and mineral samples from onland New Zealand, the offshore New Zealand region, Antarctica and worldwide. It is operated by GNS Science and, as a nationally significant database, currently receives core funding from central government. The major data contributors are GNS Science and Auckland, Massey, Waikato, Victoria, Canterbury and Otago universities, all of whom use the database as a digital catalogue for their rock and mineral collections. Petlab sample information and geoanalytical data can be uploaded, queried, viewed and downloaded at http://pet.gns.cri.nz. Petlab is a valuable tool for geoscientists in research and industry.

Tsunami runup and tide-gauge observations from the 14 November 2016 M7.8 Kaikōura earthquake, New Zealand

The 2016 Mw 7.8 Kaikōura earthquake was one of the largest earthquakes in New Zealand’s historical record, and it generated the most significant local source tsunami to affect New Zealand since 1947. There are many unusual features of this earthquake from a tsunami perspective: the epicentre was well inland of the coast, multiple faults were involved in the rupture, and the greatest tsunami damage to residential property was far from the source. In this paper, we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast, then present tsunami tide gauge and runup field observations of the tsunami that followed the Kaikōura earthquake. For the size of the tsunami, as inferred from the measured heights, the impact of this event was relatively modest, and we discuss the reasons for this which include: the state of the tide at the time of the earthquake, the degree of co-seismic uplift, and the nature of the coastal environment in the tsunami source region.

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.

Mapping surface liquefaction caused by the September 2010 and February 2011 Canterbury earthquakes: a digital dataset

ABSTRACT We present maps and digital data of the surface manifestation of liquefaction for the two major events during the 2010–2011 Canterbury earthquake sequence, the 2010 Darfield and the 2011 Christchurch earthquakes, in order to show liquefaction extent. Maps include detailed interpretation of aerial photograph mosaics and satellite images captured immediately following each event, and incorporate ground-based surveys of liquefaction occurrences. Evidence of liquefaction includes predominantly silt to fine sand and/or water ejected to the ground surface, and the presence of lateral spreading cracks (with or without ejected sediment). Liquefaction appears to be related to recent alluvial systems, and is more prevalent adjacent to existing waterways and in abandoned stream channels, where young, normally consolidated and poorly compacted sediments are water-saturated. The digital data are available for download in standard geographic information system (GIS) formats, and should provide a reference for future regional scale liquefaction studies.

New Zealand limestone purity

Geographic coordinates and lithostratigraphic names have been assigned to 2255 limestone samples that were previously analysed for soluble carbonate content. This permits, for the first time, a comparative assessment of the purity of onland New Zealand limestones by location and age. The three purest limestone populations have median CaCO3 contents of 93–97 wt%, and are from: (1) Cambrian to Early Cretaceous basement terranes, (2) Eocene–Pliocene limestones of the Chatham Islands and (3) the Eocene Ototara Limestone. These have CaCO3 contents comparable with carbonates found in isolated submarine bank settings that lack appreciable siliciclastic detritus and biogenic silica. By contrast, New Zealand Oligocene–Early Miocene limestones (Whangarei, Te Kuiti, Mahurangi, Nile Group, Otekaike and Forest Hill stratigraphic units) have median CaCO3 contents of 71–91 wt%, comparable with New Zealand Paleocene–Eocene and Middle Miocene–Pleistocene limestones. Petrographic data from a subset of 52 Otekaike and Forest Hill limestones confirm that the non-carbonate content is mostly siliciclastic sand, not glauconite. The limestone purity data support, but do not on their own prove, a hypothesis of a terrigenous source (emergent land) during the Late Oligocene-Early–Miocene maximum marine inundation of Zealandia.

Past large earthquakes on the Alpine Fault: paleoseismological progress and future directions

ABSTRACT Paleoseismology has been making an important contribution to understanding the Alpine Fault and the hazard it poses to society. However, evidence of past earthquakes comes from a wide variety of sources and publication of the evidence has been somewhat fragmented. Here, we review physical evidence for past large to great earthquakes on the Alpine Fault to summarise current understanding, illustrate progress and highlight future directions. Paleoseismic evidence has been derived from tree disturbance, landscape features and trenches across the fault. These records have been supplemented and extended back in time with sedimentary evidence of Alpine Fault earthquakes from fault-proximal lakes and wetlands. In this review, we update radiocarbon analyses using recent calibration curves and modern Bayesian statistical methods where necessary to enable comparison between on-fault, fault-proximal and off-fault earthquake records. Over recent decades, Alpine Fault paleoseismology has progressed from playing an important role in demonstrating that large surface-rupturing earthquakes occur, to enabling estimates of earthquake recurrence behaviour, shaking intensities, rupture extents, landscape response durations and likelihood of the next earthquake.

Managing hazardous materials in New Zealand’s National Petrology Reference collection

ABSTRACT New Zealand’s National Petrology Reference Collection at GNS Science includes samples of radioactive and asbestiform minerals and rocks. The legislative requirements for managing these potentially hazardous samples have recently changed because the Radiation Safety Act, Radiation Safety Regulations and Health and Safety at Work (Asbestos) Regulations were revised in 2016–2017. Steps have been taken at GNS Science to ensure legislative requirements are met, and procedures put in place to safely store and manage radioactive and asbestiform-bearing samples within the collection. These procedures may have application to other curated geological collections at New Zealand universities and museums involving potentially hazardous materials.