Building an 18 000-year-long paleo-earthquake record from detailed deep-sea turbidite characterisation in Poverty Bay, New Zealand

In :" Marine and lake paleoseismology" Special Issue. Editor(s) : D. Pantosti, E. Gràcia, G. Lamarche, and H. NelsonInternational audienceTwo 20 m-long sedimentary cores collected in two neighbouring mid-slope basins of the Paritu Turbidite System in Poverty Bay, east of New Zealand, show a high concentration of turbidites (5 to 6 turbidites per meter), interlaid with hemipelagites, tephras and a few debrites. Turbidites occur as both stacked and single, and exhibit a range of facies from muddy to sandy turbidites. The age of each turbidite is estimated using the statistical approach developed in the OxCal software from an exceptionally dense set of tephrochronology and radiocarbon ages ( 1 age per meter). The age, together with the facies and the petrophysical properties of the sediment (density, magnetic susceptibility and Pwave velocity), allows the correlation of turbidites across the continental slope (1400-2300m water depth). We identify 73 synchronous turbidites, named basin events, across the two cores between 819±191 and 17 729±701 yr BP. Compositional, foraminiferal and geochemical signatures of the turbidites are used to characterise the source area of the sediment, the origin of the turbidity currents, and their triggering mechanism. Sixty-seven basin events are interpreted as originated from slope failures on the upper continental slope in water depth ranging from 150 to 1200 m. Their earthquake trigger is inferred from the heavily gullied morphology of the source area and the water depth at which slope failures originated. We derive an earthquake mean return time of 230 yr, with a 90% probability range from 10 to 570 yr. The earthquake chronology indicates cycles of progressive decrease of earthquake return times from 400 yr to 150 yr at 0- 7 kyr, 8.2-13.5 kyr, 14.7-18 kyr. The two 1.2 kyr-long intervals in between (7-8.2 kyr and 13.5-14.7 kyr) correspond to basin-wide reorganisations with anomalous turbidite deposition (finer deposits and/or non deposition) reflecting the emplacement of two large mass transport deposits much more voluminous than the "classical" earthquake-triggered turbidites. Our results show that the progressive characterisation of a turbidite record from a single sedimentary system can provide a continuous paleo-earthquake history in regions of short historical record and incomplete onland paleoearthquake evidences. The systematic description of each turbidite enables us to infer the triggering mechanism

Submarine paleoseismology of the northern Hikurangi subduction margin of New Zealand as deduced from Turbidite record since 16 ka

International audiencePaleoseismic studies seek to characterise the signature of pre-historical earthquakes by deriving quantitative information from the geological record such as the source, magnitude and recurrence of moderate to large earthquakes. In this study, we provide a w16,000 yr-long paleo-earthquake record of the 200 km-long northern Hikurangi Margin, New Zealand, using cm-thick deep-sea turbidites identified in sediment cores. Cores were collected in strategic locations across the margin within three distinct morphological re-entrants e the Poverty, Ruatoria and Matakaoa re-entrants. The turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra. We use the Oxal probabilistic software to model the age of each turbidite, using the sedimentation rate of hemipelagite deduced from well-dated tephra layers and radiocarbon ages measurements on planktonic foraminifera. Turbidites are correlated from one core to the other using similarity in sedimentary facies, petrophysical properties and ages. Results show that 46 turbidites are synchronous along the entire margin. Amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake-triggered slope failures between 390 170 to 16,450 310 yr BP. Using well-established empirical relationships that combine peak ground acceleration, magnitude and location of earthquakes, we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region, each capable of generating Mw 7.3 to 8.4 earthquakes e two are crustal reverse faults and one is the subduction interface. The 41 Mw 7.3 earthquakes occurred at an average recurrence interval of w400 yr over the last w16,000 yr. Among them, twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of w800 yr, with alternating periods of high activity and low return times (305e610 yr) and quiescence periods with high return times (1480e2650 yr). Based on turbidite paleoseismology, we propose that subduction interface earthquakes were of lower magnitude during active periods (Mw > 7.5) than during quiescence periods (Mw 8.2)

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

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

Pre-cruise and site surveys : a synthesis of marine geological and geophysical data on the Côte d'Ivoire-Ghana transform margin

ODP Leg 159 is the first drilling cruise dedicated to assess the sedimentary, tectonic, and thermal processes as well as the subsidence history operating during and after continental transform margin formation, the challenge being to improve and develop geological models applied to this specific type of ocean-continent boundary. The location of the Côte d'Ivoire-Ghana Transform Margin, within an equatorial region and located between two different oceanic basins (Central and South Atlantic) of different ages, also provided paleoceanographic potential for Leg 159. The marine geological and geophysical surveys briefly presented above, and with which Leg 159 was planned, have already provided noteworthy data making this segment of transform margin a well-investigated example of this type. It is anticipated that continuous coring and logging at all selected Leg 159 sites will answer many of the questions still in discussion and open new trends of investigation. (Résumé d'auteur

Postglacial (after 18 ka) deep-sea sedimentation along the Hikurangi subduction margin (New Zealand): Characterisation, timing and origin of turbidites

International audienceRecent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific-Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidites deposited since c. 18 ka in the Poverty, Ruatoria and Matakaoa re-entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity. Here, alternating hemipelagite, turbidite, debrite and tephra layers reflect distinctive depositional modes of marine sedimentation, turbidity current, debris flow and volcanic eruption, respectively. Turbidites dominate the record, ranging in lithofacies from muddy to sandy turbidites, and include some basal-reverse graded turbidites inferred to be derived from hyperpycnal flows. Stacked turbidites are common and indicate multiple gravity-flows over short time periods. The chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra, which facilitate sedimentation rate calculation and identification of the origin of turbidites. Sedimentation rates range from 285 cm/ka during late glacial time (18.5-17 ka) to 15 to 109 cm/ka during postglacial time (17-0 ka). Turbidite deposition is controlled by: (1) the emplacement of slope avalanches reorganising sediment pathways; (2) the postglacial marine transgression leading to a five-fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge, and (3) the Holocene/ Pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain-size. Flood-induced turbidites are scarce: nine hyperpycnites are recognised since 18 ka and the youngest is correlated to the largest ENSO-related storm event recorded onland (Lake Tutira). Other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c. 7 ka. They yield a shorter return time (270-430 years) than the published coastal records for large earthquakes (c. 670 years), but the offshore record is likely to be more complete. The deep-sea sedimentation along the New Zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation. Climate warming and glacio-eustatic fluctuations are well recorded at a millennial timescale (18 ka), while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale (270-430 years)

Morphometric analysis of the submarine arc volcano Monowai (Tofua – Kermadec Arc) to decipher tectono-magmatic interactions

Morphometric analysis of multibeam bathymetry and backscatter data is applied to Monowai, a submarine volcano of the active Tofua–Kermadec Arc to map and document the structure and evolution of the volcanic centre. Low rates of erosion and sedimentation, and pervasive tectonic and magmatic processes, allow quantification through detailed structural analysis and measurement of deformation. The Slope, Aspect, Curvature, Rugosity, and Hydrology (flow) tools of ArcGIS provide a robust structural interpretation and the development of a model of Monowai evolution.A nested caldera structure with a volume of ~ 31 km3 and a stratovolcano of ~ 18 km3 dominate the magmatic constructs. The outer caldera is elongate along 125°, and the inner caldera along 135°. Numerous parasitic cones and fissure ridges are also observed, oriented at 039° and 041°, respectively. Northeast trending faults (with a regional average strike of 031°) are widespread within this part of the backarc, forming a nascent rift graben to the west of the Monowai caldera complex. The distribution of throw varies spatially, reaching a maximum total along-rift of 320 m and across rift of 120 m, with greater throw values measured in the west.Elongation directions of the two nested calderas are near-perpendicular to the trends of faults and fissure ridges. The inner caldera is more orthogonal to the magmatic constructs (fissure ridges and aligned vent cones) and the outer caldera is approximately orthogonal to the regional fault fabric, suggesting a strong interaction between magmatic and tectonic processes, and the directions of the horizontal principal stress. We present a detailed morphometric analysis of these relationships and the data are used to interpret the spatial and temporal evolution of the tectono-magmatic system at Monowai, and classify the type of rifting as transtensional. Similar analysis is possible elsewhere in the Kermadec backarc and within other regions of submarine volcanism

The Nippon Foundation—GEBCO Seabed 2030 Project: The Quest to See the World’s Oceans Completely Mapped by 2030

Despite many of years of mapping effort, only a small fraction of the world ocean’s seafloor has been sampled for depth, greatly limiting our ability to explore and understand critical ocean and seafloor processes. Recognizing this poor state of our knowledge of ocean depths and the critical role such knowledge plays in understanding and maintaining our planet, GEBCO and the Nippon Foundation have joined forces to establish the Nippon Foundation GEBCO Seabed 2030 Project, an international effort with the objective of facilitating the complete mapping of the world ocean by 2030. The Seabed 2030 Project will establish globally distributed regional data assembly and coordination centers (RDACCs) that will identify existing data from their assigned regions that are not currently in publicly available databases and seek to make these data available. They will develop protocols for data collection (including resolution goals) and common software and other tools to assemble and attribute appropriate metadata as they assimilate regional grids using standardized techniques. A Global Data Assembly and Coordination Center (GDACC) will integrate the regional grids into a global grid and distribute to users world-wide. The GDACC will also act as the central focal point for the coordination of common data standards and processing tools as well as the outreach coordinator for Seabed 2030 efforts. The GDACC and RDACCs will collaborate with existing data centers and bathymetric compilation efforts. Finally, the Nippon Foundation GEBCO Seabed 2030 Project will encourage and help coordinate and track new survey efforts and facilitate the development of new and innovative technologies that can increase the efficiency of seafloor mapping and thus make the ambitious goals of Seabed 2030 more likely to be achieved

Submarine mass movements and their consequences

This sixth edition of the Submarine Mass Movements and Their Consequences volume, coincident with the seventh eponymous conference includes 61 papers that span a variety of topics and are organized into nine parts as follows: (1) Submarine mass movement in margin construction and economic significance; (2) Failure dynamics from landslide geomorphology; (3) Geotechnical aspects of mass movement; (4) Multidisciplinary case studies; (5) Tectonics and mass move- ment processes; (6) Fluid flow and gas hydrates, (7) Mass transport deposits in modern and outcrop sedimentology; (8) Numerical and statistical analysis; and, (9) Tsunami generation from slope failure. The breath and quality of this body of work underpins a positive outlook and our enthusiasm for the future direction of research in this area of science as it moves towards ever more detailed analysis and monitoring. We also emphasize in this volume the need to look at mountain-scale outcrops to better understand our seismic imaging, to carry out statistical studies that draw on global data sets to better constrain broad behavioural characteristics, and to undertake numerical modelling to understand the sensitivity of a range of natural slopes.peer-reviewe

De la faille alpine à la fosse de Puysegur (Nouvelle-Zélande) : résultats de la campagne de cartographie multifaisceaux GEODYNZ-SUD, Leg 2

Le Leg 2 de la campagne GEODYNZ-SUD, menée au SW de la Nouvelle-Zélande, a permis de reconnaître les structures qui accompagnent du Nord au Sud le passage de la faille alpine à la subduction oblique sous la marge du Fiodland, puis à celle naissante, intra-océanique sous la ride de Macquarie. Au Nord et au-dessus de la plaque australienne subductée vers l'Est, un faisceau longitudinal de décrochements converge vers le système transpressif de la faille alpine en découpant la marge continentale. Au Sud, la déformation décrochante est strictement localisée au sommet de la ride de Macquarie. (Résumé d'auteur

Focused fluid seepage related to variations in accretionary wedge structure, Hikurangi margin, New Zealand

Hydrogeological processes influence the morphology, mechanical behavior, and evolution of subduction margins. Fluid supply, release, migration, and drainage control fluid pressure and collectively govern the stress state, which varies between accretionary and nonaccretionary systems. We compiled over a decade of published and unpublished acoustic data sets and seafloor observations to analyze the distribution of focused fluid expulsion along the Hikurangi margin, New Zealand. The spatial coverage and quality of our data are exceptional for subduction margins globally. We found that focused fluid seepage is widespread and varies south to north with changes in subduction setting, including: wedge morphology, convergence rate, seafloor roughness, and sediment thickness on the incoming Pacific plate. Overall, focused seepage manifests most commonly above the deforming backstop, is common on thrust ridges, and is largely absent from the frontal wedge despite ubiquitous hydrate occurrences. Focused seepage distribution may reflect spatial differences in shallow permeability architecture, while diffusive fluid flow and seepage at scales below detection limits are also likely. From the spatial coincidence of fluids with major thrust faults that disrupt gas hydrate stability, we surmise that focused seepage distribution may also reflect deeper drainage of the forearc, with implications for pore-pressure regime, fault mechanics, and critical wedge stability and morphology. Because a range of subduction styles is represented by 800 km of along-strike variability, our results may have implications for understanding subduction fluid flow and seepage globally