On the rise of strongly tilted mantle plume tails

The rise of an initially horizontal, buoyant cylinder of fluid through a denser fluid at low Reynolds number is used to look at the ascent of strongly tilted mantle plumes through the mantle. Such ascents are characterized by (1) the growth of instabilities and (2) the development of a thermal wake downstream. Three-dimensional numerical experiments were carried out to examine these features. An hybrid particle-in-cell finite element method was used to look at the rise of non-diffusing cylinders and, a standard finite element method was used to look at the diffusing case. First the experiments show that the timescale of the fastest growing instability vary with the Rayleigh number and the viscosity ratio. In particular the growth rate decreases as the Rayleigh number decreases, in agreement with our analysis of the laboratory experiments of Kerr et al. (2008). Second the experiments show that the length of the thermal wake increases with the Rayleigh number but the change in viscosity has almost no influence on the wake length. Applied to strongly tilted mantle plumes we conclude that such plumes cannot be unstable given the plume timescales. We also discuss the application of this conclusion to weakly tilted plumes. Besides, this study allows to predict that mantle plumes are unlikely to have developed a significant thermal wake by the time they reach the surface. Finally, the resolution that is required to allow for the growth of mantle plume tails by combined diffusion and thermal entrainment is shown to represent a challenge for the large scale mantle convection simulations.     

Forsterite to wadsleyite phase transformation under shear stress and consequences for the Earth's mantle transition zone

We have studied the phase transformation of forsterite to wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 °C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 °C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and wadsleyite are 65–124 wt ppm H₂O and 114–736 wt ppm H₂O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for wadsleyite, i.e., [1 0 0]{0 k l} and 1/2 〈1 1 1〉{1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone.     

Hydrologic response of underground reservoirs to seismic vibrations

The response of the water level in wells to seismic impacts from remote earthquakes and explosions are analyzed. It is shown that in most cases the magnitude of the postseismic change in the water level scales as a square root of the amplitude of the deformation wave. The intensity of persistent changes averages a dynamical deformation of 1–5 cm/μstrain. Noticeable deviations from the mentioned range are possible, depending on the particular structural features of the layer.     

A study of the effect of different solar wind streams on spacecraft functioning

The paper suggests that spacecraft equipment failures in the near-Earth environment may be caused by one of the following types of streams coming to the Earth’s orbit: (a) slow solar wind in the streamer belt or chains; (b) sporadic solar wind; (c) proton flux with an energy of E > 60 MeV. The laws of solar-terrestrial physics derived to date allow sufficiently reliable determination of the sources of these streams on the Sun as well as fairly precise calculation of their parameters and time of arrival at the Earth’s orbit. We have concluded that spacecraft maintenance and extension of their service life require timely and fairly accurate information regarding the onset of an adverse environmental effect on spacecraft. A successful solution to the problem depends mainly on the current state of the art of research and development in solar-terrestrial, ionospheric, and magnetospheric physics.     

Net ecosystem metabolism of a coastal embayment fertilised by upwelling and continental runoff

O₂, N, P and Si net ecosystem metabolism of the Ría de Ares-Betanzos (NW Iberian upwelling system) was estimated during two 3-wk periods of contrasting summer downwelling and autumn upwelling conditions by means of a transient 2-D kinematic box model. The subtidal circulation was positive in both situations, although it was depressed during downwelling and enhanced during upwelling. Concurrently, the ría was fertilised mainly by shelf bottom waters, which introduced from 69% (under downwelling) to almost 100% (under upwelling) of the limiting N nutrients. The ría was an efficient nutrient trap: about 70% of the N nutrients that entered the embayment were retained under downwelling conditions (average flushing time, 9 days) and about 50% under upwelling conditions (average flushing time 3 days). Although the trapping efficiency was lower, the net ecosystem production (NEP) was much higher under upwelling (from 1.0±0.3 to 1.5±0.4 g C m⁻² d⁻¹), than under downwelling favourable winds (from 0.2±0.1 to 0.3±0.1 g C m⁻²). The stoichiometry of NEP suggests that P and N compounds recycled faster than C compounds, specially in the inner segment of the ría. The net degree of silification was twice in the inner than in the outer segment of the ría.     

A long-term earthquake forecast for the Kuril-Kamchatka arc for the period from September 2011 to August 2016. The likely location,time, and evolution of the next great earthquake with M ≥ 7.7 in Kamchatka

We consider the results from the ongoing 2010–2011 work on long-term earthquake prediction for the Kuril-Kamchatka arc based on the pattern of seismic gaps and the seismic cycle. We develop a forecast for the next 5 years, from September 2011 to August 2016, for all segments of the Kuril-Kamchatka arc earthquake-generating zone. For 20 segments we predict the appropriate phases of the seismic cycle, the normalized rate of small earthquakes (A₁₀), the magnitudes of moderate earthquakes to be expected with probability 0.8, 0.5, and 0.15, and the maximum possible magnitudes and probability of occurrence for great (M ≥ 7.7) earthquakes. This study serves as another confirmation that it is entirely necessary to continue the work in seismic retrofitting in the area of Petropavlovsk-Kamchatskii.     

Parametric analysis of single pile response in laterally spreading ground

Extensive damage to pile-supported structures has been witnessed in several recent earthquakes (Chi-Chi, 1999; Kobe, 1995, etc.), as a result of liquefaction-induced lateral spreading of slightly sloping ground or free-face topographic irregularities. This paper presents a parametric analysis of the basic pile and soil parameters, as well as the pile-soil interaction mechanisms affecting the response of single piles subjected to such lateral spreading, based on numerical simulation with the nonlinear P-y method. In parallel, a set of design charts and analytical relations is established, for approximate computation of maximum pile deflections and bending moments, using a “theory guided” multi-variable statistical analysis of the numerical predictions. Three different combinations (design cases) of pile head constraints and soil conditions were considered, which are commonly encountered in practice. The overall accuracy of the proposed analytical relations is evaluated against experimental results from seven centrifuge and five large shaking table experiments.     

Quantifying potential propagule pressure of aquatic invasive species from the commercial shipping industry in Canada

We quantify and compare different measures of potential propagule pressure (PPP) of aquatic invasive species (AIS) from commercial vessels in Canada. We used ship arrivals and ballast water discharge volumes as proxies for PPP from ballast water organisms, and wetted surface area (WSA) as a proxy for hull fouling PPP, to determine their relative contributions to total PPP. For three regions studied, PPP proxies correlated significantly across ports and some vessel categories. Relative contributions of ship arrivals, ballast discharge, and WSAs to PPP, evidenced by non-significant correlations across these measures, varied across regions, ports, vessel types, and seasons. Flow-through (dominant on east and west coasts) and empty-refill (in Great Lakes-St. Lawrence region) were the major ballast water exchange methods employed by the vessels surveyed. These methods have different biological efficacy for AIS removal, influencing PPP. Our study illustrates benefits and limitations of using different PPP proxies to estimate invasion risk.     

Bioaccumulation depuration kinetics and effects of benzo(a)anthracene on Mytilus galloprovincialis

Polycyclic aromatic hydrocarbons (PAHs) are important environmental pollutants due to their persistence and bioaccumulation potential both in organisms and in sediments. In this study, bioaccumulation and depuration experiments were performed employing local Mediterranean mussel species, Mytilus galloprovincialis, with two biomarkers: filtration rate and lysosomal stability (neutral red retention) assay. Benzo(a)anthracene (BaA) was chosen as the model PAH compound due to its common presence in several matrices in the marine environment. Bioconcentration Factors (BCFs) for the mussels exposed to different BaA concentrations were calculated from both kinetic rate constants and from the experimental data and found between 27-3184 and 16-2745, respectively. Experimental QSAR values were found comparable to the previous QSAR models created for BaA. The effect of BaA exposure on the mussels showed a more clear dose-response relationship according to the results of lysosomal stability compared to the filtration rate.