41 research outputs found

    Double-difference tomography at Mt Etna volcano: Preliminary results

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    We performed a preliminary double-difference tomographic study using earthquake data recorded by the INGV-Catania seismic network during the large seismic and eruptive crisis of 2002-2003 at Mt Etna volcano. Compared to previous models, first results presented from the inversion of travel-time differences, tend to show an increase in the velocity contrast between the fast core and the slow periphery of the volcano

    Double-difference tomography at Mt. Etna volcano

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    Double-difference tomography at Mt Etna volcano was realized by using the tomographic algorithm developped by Monteiller et al. (2005), in which the travel-time computation was performed using a finite-difference solution of the Eikonal equation (Podvin and Lecomte, 1991) and a posteriori ray-tracing. The inverse problem was solved using a probabilistic approach (Tarantola and Valette, 1982). The optimal a priori information (correlation length and a priori model variance) was found experimentally by performing tomographies for correlation lengths and variances varying in large intervals. This probabilistic approach allowed us to use a sech pdf for representing errors in differential times. Data were travel-times and time delays provided by a set of 329 earthquakes, well-recorded by the INGV-CT seismic network (50 stations) on the Mt Etna volcano during the seismo-volcanic crisis occurring between October 2002 and January 2003. Checkerboard tests realized with this geometry and earthquake pairs showed that the model can be correctly reconstructed in a significant area around Mt Etna volcano. Results of the P and S-wave double-difference tomography clearly evidenced two concentric features: a fast central cylindrical core, probably of intrusive origin, surrounded by a slow annealed body, which could be related to partial melting

    DEFORMATION and RUPTURE of the OCEANIC CRUST MAY CONTROL GROWTH of HAWAIIAN VOLCANOES

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    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot- spot activity below the Pacific Plate(1,2). Despite the apparent simplicity of the parent process emission of magma onto the oceanic crust - the resulting edifices display some topographic complexity(3-5). Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown(6,7). Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/ oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities(8-10). Further studies are needed to determine whether such processes occur in other active intraplate volcanoes

    Stochastic Inversion of P-to-S Converted Waves for Mantle Composition and Thermal Structure: Methodology and Application

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    We present a new methodology for inverting P‐to‐S receiver function (RF) waveforms directly for mantle temperature and composition. This is achieved by interfacing the geophysical inversion with self‐consistent mineral phase equilibria calculations from which rock mineralogy and its elastic properties are predicted as a function of pressure, temperature, and bulk composition. This approach anchors temperatures, composition, seismic properties, and discontinuities that are in mineral physics data, while permitting the simultaneous use of geophysical inverse methods to optimize models of seismic properties to match RF waveforms. Resultant estimates of transition zone (TZ) topography and volumetric seismic velocities are independent of tomographic models usually required for correcting for upper mantle structure. We considered two end‐member compositional models: the equilibrated equilibrium assemblage (EA) and the disequilibrated mechanical mixture (MM) models. Thermal variations were found to influence arrival times of computed RF waveforms, whereas compositional variations affected amplitudes of waves converted at the TZ discontinuities. The robustness of the inversion strategy was tested by performing a set of synthetic inversions in which crustal structure was assumed both fixed and variable. These tests indicate that unaccounted‐for crustal structure strongly affects the retrieval of mantle properties, calling for a two‐step strategy presented herein to simultaneously recover both crustal and mantle parameters. As a proof of concept, the methodology is applied to data from two stations located in the Siberian and East European continental platforms.This work was supported by a grant from the Swiss National Science Foundation (SNF project 200021_159907). B. T. was funded by a DĂ©lĂ©gation CNRS and CongĂ© pour Recherches et Conversion ThĂ©matique from the UniversitĂ© de Lyon to visit the Research School of Earth Sciences (RSES), The Australian National University (ANU). B. T. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement 79382

    Translational toxicology in setting occupational exposure limits for dusts and hazard classification – a critical evaluation of a recent approach to translate dust overload findings from rats to humans

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    Background We analyze the scientific basis and methodology used by the German MAK Commission in their recommendations for exposure limits and carcinogen classification of “granular biopersistent particles without known specific toxicity” (GBS). These recommendations are under review at the European Union level. We examine the scientific assumptions in an attempt to reproduce the results. MAK’s human equivalent concentrations (HECs) are based on a particle mass and on a volumetric model in which results from rat inhalation studies are translated to derive occupational exposure limits (OELs) and a carcinogen classification. Methods We followed the methods as proposed by the MAK Commission and Pauluhn 2011. We also examined key assumptions in the metrics, such as surface area of the human lung, deposition fractions of inhaled dusts, human clearance rates; and risk of lung cancer among workers, presumed to have some potential for lung overload, the physiological condition in rats associated with an increase in lung cancer risk. Results The MAK recommendations on exposure limits for GBS have numerous incorrect assumptions that adversely affect the final results. The procedures to derive the respirable occupational exposure limit (OEL) could not be reproduced, a finding raising considerable scientific uncertainty about the reliability of the recommendations. Moreover, the scientific basis of using the rat model is confounded by the fact that rats and humans show different cellular responses to inhaled particles as demonstrated by bronchoalveolar lavage (BAL) studies in both species. Conclusion Classifying all GBS as carcinogenic to humans based on rat inhalation studies in which lung overload leads to chronic inflammation and cancer is inappropriate. Studies of workers, who have been exposed to relevant levels of dust, have not indicated an increase in lung cancer risk. Using the methods proposed by the MAK, we were unable to reproduce the OEL for GBS recommended by the Commission, but identified substantial errors in the models. Considerable shortcomings in the use of lung surface area, clearance rates, deposition fractions; as well as using the mass and volumetric metrics as opposed to the particle surface area metric limit the scientific reliability of the proposed GBS OEL and carcinogen classification.International Carbon Black Associatio

    An efficient algorithm for double-difference tomography and location in heterogeneous media, with an application to the Kilauea volcano.

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    International audienceImproving our understanding of crustal processes requires a better knowledge of the geometry and the position of geological bodies. In this study we have designed a method based upon double-difference relocation and tomography to image, as accurately as possible, a heterogeneous medium containing seismogenic objects. Our approach consisted not only of incorporating double difference in tomography but also partly in revisiting tomographic schemes for choosing accurate and stable numerical strategies, adapted to the use of cross-spectral time delays. We used a finite difference solution to the eikonal equation for travel time computation and a Tarantola-Valette approach for both the classical and double-difference three-dimensional tomographic inversion to find accurate earthquake locations and seismic velocity estimates. We estimated efficiently the square root of the inverse model's covariance matrix in the case of a Gaussian correlation function. It allows the use of correlation length and a priori model variance criteria to determine the optimal solution. Double-difference relocation of similar earthquakes is performed in the optimal velocity model, making absolute and relative locations less biased by the velocity model. Double-difference tomography is achieved by using high-accuracy time delay measurements. These algorithms have been applied to earthquake data recorded in the vicinity of Kilauea and Mauna Loa volcanoes for imaging the volcanic structures. Stable and detailed velocity models are obtained: the regional tomography unambiguously highlights the structure of the island of Hawaii and the double-difference tomography shows a detailed image of the southern Kilauea caldera–upper east rift zone magmatic complex
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