ALBERT

Description: [1]  Predominant stretching structures in the Greater Himalayan Crystalline Complex (GHC) trend perpendicular to the belt and are linked to southward exhumation or emplacement of the GHC between the South Tibet Detachment (STD) and the Main Central Thrust. However, our field investigations in southern Tibet reveal the widespread presence of gently dipping shear zones with a penetrative orogen-parallel stretching lineation, which separate the Tethyan Himalayan Sequence and the underlying GHC. The shear zones are well preserved in the upper part of the GHC, south to and structurally lower than the STD. Field criteria, microstructures and quartz fabrics indicate top-to-the-east shearing in the Yadong shear zone (eastern GHC), coexistence of top-to-the-east and top-to-the-west shearing in the Nyalam shear zone (central GHC), but top-to-the-west shearing in the Pulan shear zone (western GHC). Characteristic microstructures and slip systems of quartz in the high-grade GHC rocks resulted from the lateral flow under upper-amphibolite (up to 650-700 °C) to greenschist facies conditions. U-Pb ages of metamorphic zircon rims by SHRIMP and LA-MC-ICP-MS analyses yield 28-26 Ma for initiation of the Yadong and Nyalam shear zones, and 22-15 Ma for activation of the Pulan shear zone. In addition, 40 Ar/ 39 Ar cooling ages of biotite and muscovite suggest cessation of ductile sharing at 13-11 Ma on the Yadong shear zone, coeval with activation of the STD. Combined with previous studies, we propose that initiation of orogen-parallel extension marks the transition from burial/crustal thickening to exhumation of the GHC. Due to lateral crustal thickness gradients in a thickened crust, orogen-parallel gravitational collapse occurred within the convergent Himalayan orogen in the late Oligocene-Miocene. This tectonic denudation triggered and enhanced partial melting and ductile extrusion of the GHC in the Miocene.

Description: Identification of methane sources controlling hydrate distribution and concentrations in continental margins remains a major challenge in gas hydrate research. Lack of deep fluid samples and high quality regional scale seismic reflection data may lead to underestimation of the significance of fluid escape from subducting and compacting sediments in the global inventory of methane reaching the hydrate zone, the water column and the atmosphere. The distribution of concentrated hydrate zones in relation to focused fluid flow across the southern Hikurangi subduction margin was investigated using high quality, long offset (10 km streamer), pre-stack depth migrated multichannel seismic data. Analysis of low P wave velocity zones, bright-reverse polarity reflections and dim-amplitude anomalies reveals pathways for gas escape and zones of gas accumulation. The study shows the structural and stratigraphic settings of three main areas of concentrated hydrates: (1) the Opouawe Bank, dominated by focused periodic fluid input along thrust faults sustaining dynamic hydrate concentrations and gas chimneys development; (2) the frontal anticline, with a basal set of proto-thrusts controlling permeability for fluids from deeply buried and subducted sediments sustaining hydrate concentrations at the crest of the anticline; and (3) the Hikurangi Channel, with buried sand dominated channels hosting significant amounts of gas beneath the base of the hydrate zone. In sand dominated channels gas injection into the hydrate zone favors highly concentrated hydrate accumulations. The evolution of fluid expulsion controlling hydrate formation offshore southern Hikurangi is described in stages during which different methane sources (in situ, buried and thermogenic) have been dominant.

Description: The WEPTOS wave energy converter (WEC) is a novel device that combines an established and efficient wave energy absorbing mechanism with a smart structure, which can regulate the amount of incoming wave energy and reduce loads in extreme wave conditions. This adjustable A-shaped slack-moored and floating structure absorbs the energy of the waves through a multitude of rotors. The shape of the rotors is based on the renowned Salter’s Duck. On each leg, the rotors pivot around a common axle, through which the rotors transfer the absorbed power to a common power take off system. The study investigates the required capacity of the power take off (PTO) system and the structural forces on a WEPTOS WEC prototype, intended for installation at Hanstholm (Denmark), based on large scale experimental tests using a highly realistic laboratory model of the complete device. The results hereof includes the rotational speed and transmitted torque (and hereby power) to the PTO system using different PTO control strategies, the impact of fluctuations of the available mechanical power and the effect of limiting the PTO capacity on the annual energy production. Acquisition of structural forces includes mooring forces and structural bending moments in both production and extreme wave conditions, illustrating that the regulation of the angle in the A shape ensures that extreme forces on the structure can be kept in the same order of magnitude as in production conditions.

Description: Abstract. The Zintl phase Rb 7 NaSi 8 was synthesized as single-phase material. Powder and single-crystal X-ray diffraction, thermal analysis, chemical analysis, measurement of the magnetic susceptibility, and 23 Na, 29 Si, and 87 Rb nuclear magnetic resonance (NMR) spectroscopy were employed to characterize the material. Rb 7 NaSi 8 crystallizes in the Rb 7 NaGe 8 type of structure forming trigonal pyramidal anions Si 4 4– . Two unique environments of the cations are observed, the linear arrangement [Na(Si 4 ) 2 ] 7– with short Na–Si distances of 2.94 Å and the Rb2 atom coordinated by six Si 4 4– anions with long Rb–Si distances of 4.09 Å. The environment of the Rb1 atom is similar to the coordination of the rubidium atoms in Rb 4 Si 4 . The chemical bonding was investigated by quantum mechanical calculations of the electron localizability indicator (ELI), the electronic density of states (DOS), and NMR coupling parameters. Good agreement of theoretically calculated and experimentally determined NMR coupling parameters was obtained for both chemical shielding and quadrupole coupling. The anisotropy of chemical shielding (CSA) indicates an anisotropic bonding situation of the silicon atoms. This is confirmed by the observation of a lone-pair-like feature and three two-center Si–Si bonds for each silicon atom using the ELI. The electric field gradients (EFG) of 23 Na and 87 Rb indicate the anisotropy of the charge distribution of the cations. In particular, the linear arrangement [Na(Si 4 ) 2 ] 7– and the Rb1 atom feature anisotropic charge distributions of the cations. This is confirmed by calculating the anisotropy ratio defined as Δ n p = n ( p z )/(½[ n ( p x )+ n ( p y )]) with n ( p i ) corresponding to the integrated DOS of the respective state. The long distances of Rb2 to the six coordinating Si 4 4– ions are reflected by the small EFG.

Description: [1]  Episodic GPS measurements are used to quantify the present-day velocity field in the northwestern Himalaya from the southern Pamir to the Himalayan foreland. We report large postseismic displacements following the 2005 Kashmir earthquake and several mm/year thrusting of the central segment of the Salt Ranges and Potwar plateau over the foreland, westward thrusting of Nanga Parbat above the Kohistan plateau, and ~ 12 mm/yr SSE velocities of the Karakorum Ranges and of the Deosai and Kohistan plateaus relative to the Indian plate. Numerical simulations allow to determine a first approximation of slip along active faults : (1) substantial creep of ~87 mm/year between 2006 and 2012 along the flat northeast of the Balakot-Bagh thrust affected by the 2005 earthquake; (2) ~ 5 mm/year slip of the central segment of the Salt Ranges and Potwar plateau whereas their western boundaries are clearly inactive over the time span covered by our measurements; (3) 13 mm/year ductile slip along the MHT modeled by a dislocation dipping 7° northward, locked at a depth of 15 km; and (4) ~20 mm/year slip along the shear zone forming the western boundary of Nanga Parbat, between depths of 1.6 and 6.5 km. Residuals velocities suggest the existence of left-lateral strike-slip along the Jhelum fault.

Description: The 8 October 2005 Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and August 2006, in March and December 2007, and in August 2008 and 2009. Two hypotheses were tested: post-seismic displacements controlled by viscous relaxation of the lower crust or by afterslip along a flat north of the ramp affected by the main shock. A single Newtonian viscosity for the different periods cannot be determined by numerical simulations of viscous relaxation, which may indicate that the viscosity of the lower crust is non-Newtonian or that viscous relaxation does not control postseismic displacements. Numerical simulations using dislocations in a uniform elastic half-space indicate afterslip north of the ramp of the earthquake along a flat connected to the ramp. Slip along the northwestern portion of the flat accrued to about 285 mm between November 2005 and August 2006, while slip along the southeastern portion accrued to 130 mm over the same time period. Residual misfit of the observed and predicted displacements clearly indicated that afterslip is a better explanation for the observations than the hypothesis of viscous relaxation. The time evolution of the afterslip was found to be consistent with that predicted from rate-strengthening frictional sliding.

Description: ABSTRACT Morphological and seismic data from a submarine landslide complex east of New Zealand indicate flow-like deformation within gas hydrate-bearing sediment. This “creeping” deformation occurs immediately downslope of where the base of gas hydrate stability reaches the seafloor, suggesting involvement of gas hydrates. We present evidence that, contrary to conventional views, gas hydrates can directly destabilize the seafloor. Three mechanisms could explain how the shallow gas hydrate system could control these landslides. 1) Gas hydrate dissociation could result in excess pore pressure within the upper reaches of the landslide. 2) Overpressure below low-permeability gas hydrate-bearing sediments could cause hydrofracturing in the gas hydrate zone valving excess pore pressure into the landslide body. 3) Gas hydrate-bearing sediment could exhibit time-dependent plastic deformation enabling glacial-style deformation. We favor the final hypothesis, that the landslides are actually creeping seafloor glaciers. The viability of rheologically controlled deformation of a hydrate sediment mix is supported by recent laboratory observations of time-dependent deformation behavior of gas-hydrate-bearing sands. The controlling hydrate is likely to be strongly dependent on formation controls and inter-sediment hydrate morphology. Our results constitute a paradigm shift for evaluating the effect of gas hydrates on seafloor strength which, given the widespread occurrence of gas hydrates in the submarine environment, may require a re-evaluation of slope stability following future climate-forced variation in bottom water temperature.

Description: The WEPTOS wave energy converter (WEC) is a novel device that combines an established and efficient wave energy absorbing mechanism with a smart structure, which can regulate the amount of incoming wave energy and reduce loads in extreme wave conditions. This adjustable A-shaped slack-moored and floating structure absorbs the energy of the waves through a multitude of rotors. The shape of the rotors is based on the renowned Salter’s Duck. On each leg, the rotors pivot around a common axle, through which the rotors transfer the absorbed power to a common power take off system. The study investigates the required capacity of the power take off (PTO) system and the structural forces on a WEPTOS WEC prototype, intended for installation at Hanstholm (Denmark), based on large scale experimental tests using a highly realistic laboratory model of the complete device. The results hereof includes the rotational speed and transmitted torque (and hereby power) to the PTO system using different PTO control strategies, the impact of fluctuations of the available mechanical power and the effect of limiting the PTO capacity on the annual energy production. Acquisition of structural forces includes mooring forces and structural bending moments in both production and extreme wave conditions, illustrating that the regulation of the angle in the A shape ensures that extreme forces on the structure can be kept in the same order of magnitude as in production conditions.

Description: Moderate elevated vertical methane (CH4) flux is associated with sediment accretion and raised fluid expulsion at the Hikurangi subduction margin, located along the northeast coast of New Zealand. This focused CH4 flux contributes to the cycling of inorganic and organic carbon in solid phase sediment and pore water. Along a 7 km offshore transect across the Porangahau Ridge, vertical CH4 flux rates range from 11.4 mmol·m−2·a−1 off the ridge to 82.6 mmol·m−2·a−1 at the ridge base. Stable carbon isotope ratios (δ13C) in pore water and sediment were variable across the ridge suggesting close proximity of heterogeneous carbon sources. Methane stable carbon isotope ratios ranging from −107.9‰ to −60.5‰ and a C1:C2 of 3000 indicate a microbial, or biogenic, source. Near ridge, average δ13C for pore water and sediment inorganic carbon were 13C-depleted (−28.7‰ and −7.9‰, respectively) relative to all core subsamples (−19.9‰ and −2.4‰, respectively) suggesting localized anaerobic CH4 oxidation and precipitation of authigenic carbonates. Through the transect there was low contribution from anaerobic oxidation of CH4 to organic carbon pools; for all cores δ13C values of pore water dissolved organic carbon and sediment organic carbon averaged −24.4‰ and −22.1‰, respectively. Anaerobic oxidation of CH4 contributed to pore water and sediment organic carbon near the ridge as evidenced by carbon isotope values as low as to −42.8‰ and −24.7‰, respectively. Carbon concentration and isotope analyses distinguished contributions from CH4 and phytodetrital carbon sources across the ridge and show a low methane contribution to organic carbon.

Description: Powder samples as well as red and transparent single crystals of the Zintl phase Cs 7 NaSi 8 were synthesized and characterized by means of X-ray diffraction and differential thermal analysis. Cs 7 NaSi 8 was found to be isotypic to the recently reported phase Rb 7 NaSi 8 . It crystallizes in the Rb 7 NaGe 8 structure type forming trigonal pyramidal Si 4 4– anions. Two unique environments of the cations are observed, a linear arrangement [Na(Si 4 ) 2 ] 7– with short Na–Si distances of 3.0 Å and a Cs2 atom coordinated by six Si 4 4– anions with long Cs–Si distances of 4.2 Å. The bonding situation was investigated by a combined application of 29 Si, 23 Na, and 133 Cs solid-state NMR spectroscopy and quantum mechanical calculations of the NMR coupling parameters. In addition the electronic density of states (DOS), the electron localizability indicator (ELI) and the atomic charges using the QTAIM approach were studied. Good agreement of the calculated and experimental values of the NMR coupling parameters was obtained. An anisotropic bonding situation of the silicon atoms is indicated by the chemical shift anisotropy being similar to Rb 7 NaSi 8 . Confirmation is given by the observation of one lone-pair-like feature for each silicon atom and two types of two-center Si–Si bonds using the ELI. Calculation and NMR spectroscopic determination of the 23 Na and 133 Cs electric field gradients prove anisotropies of the charge distribution around the cations. Due to the similar values for the Na atoms in M 7 NaSi 8 ( M = Rb, Cs) equal bonding situations can be concluded. The much larger anisotropy of the charge distribution of the Cs atoms can be addressed as the main difference to Rb 7 NaSi 8 .