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

Comparing P and S wave heterogeneity in the mantle

From the reprocessed data set of Engdahl and co-workers we have carefully selected matching P and S data for tomographic imaging. We assess data and model error and conclude that our S model uncertainty is twice that of the P model. We account for this in our comparison of the perturbations in P and S-wavespeed. In accord with previous studies we find that P and S perturbations are positively correlated at all depths. However, in the deep mantle systematic di fferences occur between regions that have undergone subduction in the last 120 million years and those that have not. In particular, below 1500 km depth ∂ ln Vs/∂ ln Vp is signifi cantly larger in mantle regions away from subduction than in mantle beneath convergent margins. This inference is substantiated by wavespeed analyses with random realizations of the slab/non-slab distribution. Through much of the mantle there is no signi ficant correlation between bulk sound and S-wave perturbations, but they appear to be negatively correlated between 1700 and 2100 km depth, which is also where the largest di erences in ∂ ln Vs/∂ ln Vp occur. This finding supports convection models with compositional heterogeneity in the lowermost mantle

Intensive care patients with influenza A (H1N1) infection in Iceland 2009

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn Skoða/Opna(view/open)BACKGROUND: We describe the main characteristics of patients that required intensive care due to the influenza (H1N1) outbrake in 2009. METHODS: Retrospective and prospective analysis of medical records from patients admitted to ICU with positive RT-PCR for (H1N1). RESULTS: During a six week period in the fall of 2009, 16 patients were admitted to intensive care in Iceland with confirmed H1N1 infection. Mean age was 48 years (range 1-81). Most patients were considered quite healthy but the majority had risk factors such as smoking, obesity or hypertension. All but one had fever, cough, dyspnea and bilateral infiltrates on chest x-ray and developed any organ failures (mean SOFA score 7). 12 needed mechanical ventilation and two extra corporeal membrane oxygenation (ECMO). Mean APACHE II score was 20. No patient died in the ICU but one elderly patient with multiple underlying diseases died a few days after being discharged from the ICU. CONCLUSIONS: (1) The incidence of severe influenza A (H1N1) that leads to ICU admission appears to be high in Iceland. (2) Many patients developed acute respiratory distress syndrome in addition to other organ failures, and required additional measures for oxygenation such as prone position, nitric oxide inhalation and ECMO. (3) 28 day mortality was low. (4) This study will aid in future outbreak planning in Iceland. Key words: influenza A, pneumonia, multiple organ failure, death rate, intensive care, ventilator therapy, ECMO.Tilgangur: Að lýsa helstu einkennum og afdrifum þeirra sem lögðust inn á gjörgæsludeildir á Íslandi vegna inflúensusýkingar af A stofni (H1N1) haustið 2009. Aðferðir: Aflað var upplýsinga um sjúklinga sem lögðust inn á gjörgæsludeildir á Íslandi með staðfesta H1N1 2009 sýkingu. Niðurstöður: 16 sjúklingar lögðust inn á gjörgæsludeildir vegna inflúensu A (H1N1) sýkingar, meðalaldur 48 ár (1-81). Flestir töldust vera tiltölulega frískir fyrir, en 13 höfðu þó sögu um reykingar, offitu eða háþrýsting. 15 höfðu hita, hósta, öndunarþyngsli og dreifðar íferðir í báðum lungum á lungnamynd og margir fengu fjöllíffærabilun. Allir fengu veirulyf og 12 voru meðhöndlaðir í öndunarvél, þar af tveir einnig í hjarta- og lungnavél. Enginn sjúklingur lést á gjörgæsludeild, en einn fjölveikur aldraður sjúklingur lést síðar á legudeild. Ályktanir: (1) Tíðni alvarlegra sjúkdómseinkenna af völdum inflúensu A (H1N1) sem leiða til gjörgæslumeðferðar er há á Íslandi. (2) Þessir sjúklingar fá flestir, auk annarra líffæratruflana, mjög alvarlega öndunarbilun sem oft lætur ekki undan hefðbundinni öndunarvélameðferð. (3) Árangur meðferðar á íslenskum gjörgæsludeildum hefur verið góður. (4) Niðurstöður þessarar rannsóknar geta nýst yfirvöldum við mat á meðferðarmöguleikum og fyrirbyggjandi aðgerðum gegn þessum lífshættulega sjúkdómi

The Slab Puzzle of the Alpine‐Mediterranean Region: Insights from a new, High‐Resolution, Shear‐Wave Velocity Model of the Upper Mantle

Mediterranean tectonics since the Lower Cretaceous has been characterized by a multi‐phase subduction and collision history with temporally and spatially‐variable, small‐scale plate configurations. A new shear‐wave velocity model of the Mediterranean upper mantle (MeRE2020), constrained by a very large set of over 200,000 broadband (8‐350 s), inter‐station, Rayleigh‐wave, phase‐velocity curves, illuminates the complex structure and fragmentation of the subducting slabs. Phase‐velocity maps computed using these measurements were inverted for depth‐dependent, shear‐wave velocities using a stochastic particle‐swarm‐optimization algorithm (PSO). The resulting three‐dimensional (3‐D) model makes possible an inventory of slab segments across the Mediterranean. Fourteen slab segments of 200‐800 km length along‐strike are identified. We distinguish three categories of subducted slabs: attached slabs reaching down to the bottom of the model; shallow slabs of shorter length in down‐dip direction, terminating shallower than 300 km depth; and detached slab segments. The location of slab segments are consistent with and validated by the intermediate‐depth seismicity, where it is present. The new high‐resolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the Mediterranean realm

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

Tomographic imaging of the lowermost mantle with differential times of refracted and diffracted core phases (PKP, Pdiff)

The mapping of variations in P wave speed in the deep mantle is restricted by the uneven sampling of P waves, in particular beneath the Southern Hemisphere. To enhance data coverage, we augmented the ∼1.6 million summary rays of P, pP, and pwP that we used in previous studies with differential travel times of diffracted and refracted core phases. The joint inversion puts better constraints on the long‐wavelength variations in the very deep mantle and yields an increase in the amplitude of velocity perturbations near the CMB that is in agreement with but still smaller than inferences from shear wave studies. Resolution tests indicate that in some regions the enhanced definition of structure is significant, but in most regions the improvements are subtle and structure remains poorly resolved in large regions of the mantle

Constraints on mantle convection from seismic tomography

Since the advent of global seismic tomography some 25 years ago, advances in technology, seismological theory, and data acquisition have allowed spectacular progress in our ability to image seismic heterogeneity in Earth's mantle. We briefly review some concepts of seismic tomography, such as parameterization

Tomographic imaging of the lowermost mantle with differential times of refracted and diffracted core phases (PKP, Pdiff)

The mapping of variations in P wave speed in the deep mantle is restricted by the uneven sampling of P waves, in particular beneath the Southern Hemisphere. To enhance data coverage, we augmented the ∼1.6 million summary rays of P, pP, and pwP that we used in previous studies with differential travel times of diffracted and refracted core phases. The joint inversion puts better constraints on the long‐wavelength variations in the very deep mantle and yields an increase in the amplitude of velocity perturbations near the CMB that is in agreement with but still smaller than inferences from shear wave studies. Resolution tests indicate that in some regions the enhanced definition of structure is significant, but in most regions the improvements are subtle and structure remains poorly resolved in large regions of the mantle

Epeirogenic uplift above a detached slab in northern Central America

P-wave tomographic images reveal that the northern Central America highlands east of the modern volcanic arc overlie a detached slab. Hypsometric analysis of the highlands in Honduras demonstrates that the region is a dissected plateau that is disrupted by normal faults near the North American–Caribbean plate margin. The dissected Central American plateau contains a network of superimposed rivers with meanders cut into bedrock; such a geomorphic character indicates that the regional uplift occurred in the absence of tilting. We propose that the epeirogenic uplift of northern Central America is the buoyant upper-plate response to the influx of mantle asthenosphere following the breakoff and sinking of the slab

4-D evolution of SE Asia mantle structure from geological reconstructions and seismic tomography

How the collision between India and Asia is related to processes deeper in the mantle is unclear. Here we compare geological reconstructions of block motions within Asia since W50 Ma with the tomographically imaged threedimensional (3-D) morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure. Past positions of the convergent margin show remarkable similarities with slab geometry at specific depths. The striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision. The slab contours match the progressive deformation of Asia’s margin, including India’s indentation and Sundaland’s extrusion. Ever since the onset of collision, the Indian plate appears to have overridden its own sinking mantle and it does not seem, at present, to underthrust Tibet significantly north of the Zangbo suture. If correct, this observation would provide further evidence against models of plateau build-up involving Indian lithosphere. The tomographic images beneath India confirm that Asian deformation has absorbed at least (circa) 1500 km of convergence since collision began. From the match between the southeastward motion of Sundaland between 40 and 20 Ma and the principal change in slab structure between 700 and 1100 km depths, we infer that lateral advection in the mantle is small and that the sinking rate beneath Sunda was circa 2 cm/yr in the lower mantle and circa 5 cm/yr above the transition zone