Multibeam bathymetric surveys of submarine volcanoes and mega-pockmarks on the Chatham Rise, New Zealand

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in New Zealand Journal of Geology and Geophysics 54 (2011): 329-339, doi:10.1080/00288306.2011.589860.Multibeam bathymetric surveys east of the South Island of New Zealand present images of submarine volcanoes and pockmarks west of Urry Knolls on the Chatham Rise, and evidence of submarine erosion on the southern margin of the Chatham Rise. Among numerous volcanic cones, diameters of the largest reach ~2000 m, and some stand as high as 400 m above the surrounding seafloor. The tops of most of the volcanic cones are flat, with hints of craters, and some with asymmetric shapes may show flank collapses. There are hints of both northeast-southwest and northwest-southeast alignments of volcanoes, but no associated faulting is apparent. Near and to the west of these volcanoes, huge pockmarks, some more than ~1 km in diameter, disrupt bottom topography. Pockmarks in this region seem to be confined to sea floor shallower than ~1200 m, but we see evidence of deeper pockmarks at water depths of up to 2100 m on profiles crossing the Bounty Trough. The pockmark field on the Chatham Rise seems to be bounded on the south by a trough near 1200 m depth; like others, we presume that contour currents have eroded the margin and created the trough.This research was supported by the National Science Foundation under grants EAR-0409564, EAR-0409609, and EAR-0409835.2012-08-3

QUINTUPLETS D'ISOSPIN DES NOYAUX DE MASSE 16

Deux méthodes de perturbation sont proposées pour rendre compte des niveaux T = 2 de 16O. La première est basée sur la connaissance des fonctions d'onde des états T = 1. La seconde est la " H. R. P. A. " avec un état fondamental non perturbé (Tamm Dancoff). Les résultats sont en accord avec l'expérience.Two perturbation methods are proposed in order to describe the T = 2 levels of 16O. The first one based on the knowledge of the T = 1 states wave functions. The second one is the " H. R. P. A. " with unperturbed ground state (Tamm Dancoff). The results are in agreement with experiment

Monitoring of natural oil seepage in the Lower Congo Basin using SAR observations.

International audienceSynthetic Aperture Radar (SAR) is a spaceborne tool allowing near real-time imagery over large ground footprints of areas hundreds of kilometres wide. SAR also allows persistent observations of the process of oil discharges, benefiting from (1) day and night observations, (2) independence of cloud cover and (3) high revisiting frequencies. The interpretation of 82 SAR scenes over the Lower Congo Basin for the 1994–2012 period allowed the recognition of 1400 natural seepage slicks associated with 102 individual seep sites. We acquired an additional SAR data set with a short revisit time over a selected prolific area. The data set consisted of 22 SAR scenes acquired over a 10-day period, meaning a maximum revisiting period of 12 h between subsequent SAR acquisitions. The short-term approach shows that seepage slicks were detected with wind speeds between 1.5 and 6.5 m/s (2.91 to 12.63 knots). Both long-term and short-term monitoring evidences that seepage events are intermittent, with the occurrence rate of oil release ranging from 5 to 80%. Short-term monitoring shows that the seepage pace is independent between seep sites, suggesting contrasted controlling factors. It also shows that the residence time of seepage slicks is systematically shorter than 12 h, which is far below reported values. Understanding the seepage slick residence time is essential to provide an accurate estimation of the fluid flow and to compute the volumetric outflow. The integration of in-situ mooring points measuring the current velocity 10 m below the sea surface, in addition to local wind field and slick length, allowed us to more accurately estimate the residence time of oil slicks at the sea surface before vanishing. The results show that the sea surface residence time of oil slicks is limited to a few hours, with a median value of 3 h 15 min. These new residence time estimations allowed us to propose a quantification of the regional oil output in the Lower Congo Basin, estimated at 4380 m³/year. This area may therefore be considered as the world's third biggest oil-supplying province from natural leakages

Influence of fluid overpressure on sliding with or without frontal buttress. Insights from analytical and experimental modeling

Poste

Transform continental margins - Part 2: A worldwide review

International audienceWe present a global inventory of transform continental margins, based on both a worldwide comparison of continent-ocean boundary identifications with oceanic fracture zones traces, and a compilation of published regional studies. This inventory increases the number of identified transform margins from 29 to 78. These margins represent 16% of continental margins in cumulative length and 31% of non-convergent margins. We include morphological data, published upper crustal sections, continent to ocean transition locations and published Moho shape data in the new database. This review confirms that continent to ocean transitions are sharper at transform margins than at divergent margins. It also emphasizes the structural diversity of transform margins. Associated with one third of transform margins, we define marginal plateaus as a new type of relief that corresponds to a flat but deep surface inside the continental slope, and that may be inherited from crustal thinning prior to transform faulting. Transform margin initiation appears to be favoured along propagating oceans and within cold and thick lithospheres