Geoffroy Lamarche

University of Auckland

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Philip M. Barnes

National Institute of Water and Atmospheric Research

VL Lucieer

University of Tasmania

Joshu J. Mountjoy

National Institute of Water and Atmospheric Research

Arne Pallentin

National Institute of Water and Atmospheric Research

Xavier Lurton

Ifremer

Alan R. Orpin

National Institute of Water and Atmospheric Research

Jean‐Yves Collot

Institut de Recherche pour le Développement

Jonathan M. Bull

National Oceanography Centre

Sally Watson

National Institute of Water and Atmospheric Research

Jean‐Noël Proust

Géosciences Rennes

Cooperative Institutions

GNS Science

111

National Institute of Water and Atmospheric Research

Centre National de la Recherche Scientifique

Victoria University of Wellington

University of Auckland

University of Canterbury

Consejo Superior de Investigaciones Científicas

National Oceanography Centre

GEOMAR Helmholtz Centre for Ocean Research Kiel

United States Geological Survey

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GEODYNZ-SUD shipboard report : Leg Hikurangi, 1-18 november 1993, Leg Puysegur, 21 november-07 december 1993

Jean‐Yves Collot J. Delteil K. Lewis J.C. Audru P. Barnes

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Tsunami hazard potential for the equatorial southwestern Pacific atolls of Tokelau from scenario-based simulations

Natural hazards and earth system sciences (2016)

Alan R. Orpin G. J. Rickard Peter Gerring Geoffroy Lamarche

Abstract. Devastating tsunami over the last decade have significantly heightened awareness of the potential consequences and vulnerability of low-lying Pacific islands and coastal regions. Our appraisal of the potential tsunami hazard for the atolls of the Tokelau Islands is based on a tsunami source–propagation–inundation model using Gerris Flow Solver, adapted from the companion study by Lamarche et al. (2015) for the islands of Wallis and Futuna. We assess whether there is potential for tsunami flooding on any of the village islets from a selection of 14 earthquake-source experiments. These earthquake sources are primarily based on the largest Pacific earthquakes of Mw ≥ 8.1 since 1950 and other large credible sources of tsunami that may impact Tokelau. Earthquake-source location and moment magnitude are related to tsunami-wave amplitudes and tsunami flood depths simulated for each of the three atolls of Tokelau. This approach yields instructive results for a community advisory but is not intended to be fully deterministic. Rather, the underlying aim is to identify credible sources that present the greatest potential to trigger an emergency response. Results from our modelling show that wave fields are channelled by the bathymetry of the Pacific basin in such a way that the swathes of the highest waves sweep immediately northeast of the Tokelau Islands. Our limited simulations suggest that trans-Pacific tsunami from distant earthquake sources to the north of Tokelau pose the most significant inundation threat. In particular, our assumed worst-case scenario for the Kuril Trench generated maximum modelled-wave amplitudes in excess of 1 m, which may last a few hours and include several wave trains. Other sources can impact specific sectors of the atolls, particularly distant earthquakes from Chile and Peru, and regional earthquake sources to the south. Flooding is dependent on the wave orientation and direct alignment to the incoming tsunami. Our "worst-case" tsunami simulations of the Tokelau Islands suggest that dry areas remain around the villages, which are typically built on a high islet. Consistent with the oral history of little or no perceived tsunami threat, simulations from the recent Tohoku and Chile earthquake sources suggest only limited flooding around low-lying islets of the atoll. Where potential tsunami flooding is inferred from the modelling, recommended minimum evacuation heights above local sea level are compiled, with particular attention paid to variations in tsunami flood depth around the atolls, subdivided into directional quadrants around each atoll. However, complex wave behaviours around the atolls, islets, tidal channels and within the lagoons are also observed in our simulations. Wave amplitudes within the lagoons may exceed 50 cm, increasing any inundation and potential hazards on the inner shoreline of the atolls, which in turn may influence evacuation strategies. Our study shows that indicative simulation studies can be achieved even with only basic field information. In part, this is due to the spatially and vertically limited topography of the atoll, short reef flat and steep seaward bathymetry, and the simple depth profile of the lagoon bathymetry.

Atoll

Tsunami earthquake

Typhoon

10.5194/nhess-16-1239-2016

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R.V. Sonne New Vent Survey SO191. Multi-Channel Seismic Reflection Regional Survey

Philip M. Barnes Geoffroy Lamarche Ingo A. Pecher Jörg Bialas

German Research Vessel R.V. Sonne visited New Zealand early this year to initiate a large collaborative research program involving IFM-GEOMAR (Germany), GNS Science and a number of New Zealand university. The aim of the project is to study gas hydrates in the offshore region of the North Island east coast, and in particular, to investigate local and regional processes of methane transport and the characterization of facies at cold vents and gas hydrate deposits along the Hikurangi margin. The survey included three legs from 11 January to 23 March 2007, during which a variety of geophysical, geochemical, biological and environmental data where acquired. The geophysical data will help investigate the structures, fluid flow conduits and possible connections to deeper fluid sources of vent sites.

Seismic survey

Geological survey

Sonne

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Building capability for in situ quantitative characterisation of the ocean water column using acoustic multibeam backscatter data. Catalyst: Seeding Activity Report

Geoffroy Lamarche VL Lucieer

The objective of this project was to enhance our ability to develop protocols and methodologies for identifying and quantifying features such as gas, oil, and freshwater in the ocean using marine acoustic technology. Such approaches are still in their infancy but since New Zealand has sovereign rights over 4,000,000 km 2 of ocean in which resources (fish, minerals, hydrocarbons) are vast but mostly unquantified, they potentially provide considerable economic, environmental and cultural benefits to New Zealand by improving our capacity to manage our marine estate. This project has established a multidisciplinary research consortium of internationally recognised experts in marine acoustics and geophysics, spatial analysis and environment, from New Zealand (NIWA, University of Auckland), France (CNRS-Geosciences Rennes, IFREMER), Australia (Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania - IMAS-UTAS), USA (University of New Hampshire, Centre for Coastal and Ocean Mapping - UNH-CCOM), Germany (GEOMAR), and Belgium (FPS Economy). During the April 2017 workshop, in Rennes, France, we reviewed the state of scientific and technological knowledge on water column data, identified key technical issues (data acquisition, use and transfer), and designed the concept of an ambitious marine geophysical survey in New Zealand required to address the key scientific questions. During year two, we finalised an ambitious multi-institute survey proposal. The project culminated in a New Zealand funded 20-day voyage of R.V. Tangaroa to which twenty participants from 8 organisations brought specific expertise and equipment. The acoustic survey focused on a large active hydrothermal vent field in the Bay of Plenty and resulted in the collection of an outstanding marine acoustic and ground truthing dataset over intensive methane and CO 2 vents. Our survey proved exceptionally successful and demonstrated the potential to differentiate methane and CO 2 bubbles in the water column. A result thought impossible up until now. The research will lead to multiple collaborative publication

Marine geology

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Analysis of Backscatter and Seafloor Acoustical Properties for Geosciences and Biodiversity Mapping Studies in Cook Strait, New Zealand

The Journal of the Acoustical Society of America (2008)

Xavier Lurton Geoffroy Lamarche Anne-Laure Verdier Jean‐Marie Augustin I. C. Wright

A quantitative analysis was conducted over sonar backscatter data collected on the Cook Strait region, central New Zealand, featuring multibeam (̃ 30 kHz) bathymetry and backscatter data, groundtruthed by an extensive geological database (photographs, seabed samples, high-resolution seismics). A first processing step removes the effects of the sounder, seafloor topography, and water column. A second step includes sonar image mosaicing, signal calibration and compensation, speckle noise filtering, image segmentation and textural analysis. Backscatter angular dependence is then extracted from the raw data accounting for the co-registered multibeam bathymetry; it is linked to the various facies of this geologically very active region, forming a catalogue usable for future investigation. Some local features are analysed in details, referring to the geological local context. Also the backscatter data from the Haungaroa volcano were used for a proof-of-concept biodiversity mapping exercise. Ecological theory was utilised to predict biodiversity from the seabed substrate heterogeneity, derived from the segmentation of the backscatter data properly pre-processed. The backscatter analysis resulted in the identification of local features with geological, sedimentological, topographic, and possibly biological significance, otherwise not recognised with conventional surveying. This emphasises the potential of backscatter data in submarine seismic hazard studies and large-scale biodiversity mapping.

Backscatter (email)

Seabed

Seafloor Spreading

10.1121/1.2934856

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On the lookout for tectonic faults and underwater landslides

Geoffroy Lamarche

Because New Zealand straddles an active tectonic plate boundary, our coastal communities are vulnerable to earthquake and tsunami hazards. Explains how NIWA scientists are learning more about the sources and impacts of large-magnitude earthquakes and submarine landslides off our coasts.

Submarine landslide

Tsunami earthquake

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From oblique subduction to intra-continental transpression: Structures of the southern Kermadec-Hikurangi margin from multibeam bathymetry, side-scan sonar and seismic reflection

Marine Geophysical Research (1996)

Jean‐Yves Collot Jean Delteil K. B. Lewis Bryan Davy Geoffroy Lamarche

Seamount

Transpression

Pacific Plate

Obduction