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

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

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 Délégation CNRS and Congé pour Recherches et Conversion Thématique from the Université 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

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

Migration of seismic activity associated with phreatic eruption at Merapi volcano, Indonesia

Phreatic activity of Merapi started after nearly 2 years of quiescence following the October-November 2010 eruption which was the largest in more than 100 years. A dozen eruptions identified by visual andior seismic observations took place between August 2012 and April 2014. We present in this work the results of a detailed analysis of the April 20, 2014 phreatic eruption. We attempted to reconstruct the eruptive process, which lasted for over 30 min. To this end, we determined the wavefield composition by polarization analysis, located high-frequency earthquakes occurring in the initial part of the eruption process and then determined the seismic source migration of low-frequency part of the tremor-like signal [0.3-3 Hz] over time. Source depth of low-frequency signal was obtained by comparing the slowness vector calculated using 3 stations of the seismic antenna with a slowness vector model obtained by ray tracing in the structure, taking into account the topography and a 1D velocity model obtained by spatial auto-correlation analysis. The results allow to distinguish 3 different phases: 1) High-frequency transients interpreted as the result of a sudden decompression caused by the transition of the volcanic fluid to a gaseous phase that occurred approximately 1.5 km deep. This decompression process in the hydrothermal system generated a migration of the low-frequency seismic source from 900 m to 1800 m above sea level: 2) A second decompression process revealed by high-frequency micro-seismicity and associated to the migration of the low-frequency tremor source which is marked first by a descent phase, followed by a sharp ascent until reaching the surface. The evolution of the back-azimuth during the migration process indicates a slight inclination of the conduit, presumably in the orientation of the dome fracture, in the NW-SE direction. This direction is consistent with the alignment of regional tectonic structures and with the directivity of eruption deposits. 3) The seismic source then remains positioned at the altitude of the dome for over 10 min. This phase probably corresponds to the ash emission process. The average migration speed of the low-frequency seismic source from the starting eruptive process to ash emission is about 5 m/s