Age-dependent seismic thickness and mechanical strength of the Australian lithosphere

We present constraints on the regional variations of the seismic and mechanical thickness of the Australian lithosphere. We infer the seismic thickness from a waveform tomographic model of S-wave speed, and as a proxy for the elastic thickness we use the wavelength at which the coherence of surface topography and Bouguer gravity drops below half of its long-wavelength maximum. Our results show that on scales <1000 km the relationship between the age of the crust and the thickness of the lithosphere is more complicated than longer-wavelength or global averages suggest. Recent geochemical and geodynamical evidence for small-scale secular variations of the composition and stability of continental cratons further illustrates the complexity of the age dependence of seismo-mechanical lithospheric properties on regional scales

Computing dispersal of atmospheric pollutants near airports

Computing dispersal of atmospheric pollutants near airports by use of mean wind and temperature profile

A preliminary sensitivity analysis of the coupled diffusion and chemistry model

The sensitivity of the coupled chemistry/diffusion model's outputs to a wide range of variation of the model's independent variables has been investigated. It is shown that the efficiency with which the now catalytic cycle destroys ambient O3 is extremely sensitive to the amount of NO emitted and to the relative rates of turbulent diffusion and chemical reactions. For representative conditions in the stratosphere, a tenfold variation of either the turbulence intensity or the reaction rate constant or the source strength can vary the efficiency from 1% to 50%. If the duration of Phase 3 is a significant fraction of the total residence time of the plume, then these efficiency variations can alter O3 depletion rates by more than a factor of two. These results, therefore, point toward those variables which must be accurately defined or measured if one is to adequately predict the effect of SST operations on the ambient inventory of O3 in the lower stratosphere

Tomographic evidence for compositional heterogeneity deep in earth’s mantle

In the past decade, tomographic imaging has revealed that trajectories of mantle convection are more complex than expected from end-member models of unhindered whole mantle circulation or layered convection with an interface at 660 km depth. In the context of recently proposed mantle flow models, we discuss evidence for compositional heterogeneity in the deepest 1000 km of the mantle, and describe how this could survive in a system of thermochemical convection

Stage of development, governance and performance of inter-firm innovation cooperation: a conceptual model and propositions

International audienceThis paper presents a framework for the dyadic study of inter-firm innovation cooperation, beyond the boundaries of collaborative innovation projects. In order to understand how two firms can maximize the performance of their relationship, we performed a literature review combined with interviews with practitioners. The result of this study is a model associated with propositions on the interactions between its different elements, which are (i) the governance of the relationship, (ii) its performance, (iii) its level of development and (iv) the degree of innovation of the collaborative projects. This paper concludes by suggesting future researches and stating implications for managers

Isolated deep earthquakes beneath the North Island of New Zealand

Seismicity shallows towards the south along the Tonga-Kermadec-Hikurangi margin, deep and intermediate seismicity being absent altogether in the South Island of New Zealand. Beneath the Taranaki region of the North Island the maximum depth of the main seismicity is 250 km, but very rare events occur directly below at 600 km. These could be associated with a detached slab or a vertical, aseismic continuation of the subducted Pacific Plate. Six small events that occurred in the 1990s were recorded extensively by digital instruments of the New Zealand National Network (NZNN) and temporary deployments. We relocate these events by a joint hypocentre determination (JHD) method and find their focal mechanisms using first motions and relative amplitudes of P and S arrivals. The earthquakes relocate to a remarkably uniform depth of 603 +/- 3 kmrelative error (+/- 10 km absolute error) in a line 30- km long orientated 40 NE, roughly parallel to the strike of the intermediate- depth seismicity. The only consistent component of the focal mechanisms is the tension axis: all lie close to horizontal and tend to align with the line of hypocentres. We interpret this deep seismic zone as a detached sliver of plate lying horizontally with the same orientation as the main subducted plate above. Volume change caused by a phase change controlled by the pressure at 600 km and temperature in the sliver produces a pattern of strain that places the sliver under tension along its lengt

Early Purchaser Involvement in Open Innovation- the case of an advanced purchasing function triggering the absorption of external knowledge in the French automotive industry

International audienceThis paper investigates the mechanisms that trigger the absorption of external knowledge in an innovative French automotive firm. An ethnographic-inspired study conducted by an academic embedded within the Innovation Purchasing Department has enable us to present a rare and new function of Purchasing that plays an important role between potential new suppliers and Research and Development personnel

Some analyses of the chemistry and diffusion of SST exhaust materials during phase 3 of the wake period

In the generally stably stratified lower stratosphere, SST exhaust plumes could spend a significant length of time in a relatively undispersed state. This effort has utilized invariant modeling techniques to simulate the separate and combined effects of atmospheric turbulence, turbulent diffusion, and chemical reactions of SST exhaust materials in the lower stratosphere. The primary results to date are: (1) The combination of relatively slow diffusive mixing and rapid chemical reactions during the Phase III wake period minimizes the effect of SST exhausts on O3 depletion by the so-called NOx catalytic cycle. While the SST-produced NO is substantially above background concentrations, it appears diffusive mixing of NO and O3 is simply too slow to produce the O3 depletions originally proposed. (2) The time required to dilute the SST exhaust plume may be a significant fraction of the total time these materials are resident in the lower stratosphere. If this is the case, then prior estimates of the environmental impact of these materials must be revised significantly downward

Compositional heterogeneity in the bottom 1000 kilometers of earth's mantle : Toward a hybrid convection model

Tomographic imaging indicates that slabs of subducted lithosphere can sink deep into Earth's lower mantle. The view that convective flow is stratified at 660-kilometer depth and preserves a relatively pristine lower mantle is therefore not tenable. However, a range of geophysical evidence indicates that compositionally distinct, hence convectively isolated, mantle domains may exist in the bottom 1000 kilometers of the mantle. Survival of these domains, which are perhaps related to local iron enrichment and silicate-to-oxide transformations, implies that mantle convection is more complex than envisaged by conventional end-member flow models

Zoned mantle convection

We review the present state of our understanding of mantle convection with respect to geochemical and geophysical evidence and we suggest a model for mantle convection and its evolution over the Earth’s history that can reconcile this evidence. Wholemantle convection, even with material segregated within the D00 region just above the core{mantle boundary, is incompatible with the budget of argon and helium and with the inventory of heat sources required by the thermal evolution of the Earth. We show that the deep-mantle composition in lithophilic incompatible elements is inconsistent with the storage of old plates of ordinary oceanic lithosphere, i.e. with the concept of a plate graveyard. Isotopic inventories indicate that the deep-mantle composition is not correctly accounted for by continental debris, primitive material or subducted slabs containing normal oceanic crust. Seismological observations have begun to hint at compositional heterogeneity in the bottom 1000 km or so of the mantle, but there is no compelling evidence in support of an interface between deep and shallow mantle at mid-depth. We suggest that in a system of thermochemical convection, lithospheric plates subduct to a depth that depends|in a complicated fashion|on their composition and thermal structure. The thermal structure of the sinking plates is primarily determined by the direction and rate of convergence, the age of the lithosphere at the trench, the sinking rate and the variation of these parameters over time (i.e. platetectonic history) and is not the same for all subduction systems. The sinking rate in the mantle is determined by a combination of thermal (negative) and compositional buoyancy and as regards the latter we consider in particular the e¬ect of the loading of plates with basaltic plateaux produced by plume heads. Barren oceanic plates are relatively buoyant and may be recycled preferentially in the shallow mantle. Oceanic plateau-laden plates have a more pronounced negative buoyancy and can more easily founder to the very base of the mantle. Plateau segregation remains statistical and no sharp compositional interface is expected from the multiple fate of the plates. We show that the variable depth subduction of heavily laden plates can prevent full vertical mixing and preserve a vertical concentration gradient in the mantle. In addition, it can account for the preservation of scattered remnants of primitive material in the deep mantle and therefore for the Ar and 3He observations in oceanisland basalts