First recorded eruption of Nabro volcano, Eritrea, 2011

We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of re- gional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodi- gious quantity of SO2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic signifi- cance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of Editorial responsibility: G. Giordano the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shal- low, NW–SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response miti- gated the human costs of the eruption

Rapid response to the M_w 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics

Numerical Simulation of the Atmospheric Signature of Artificial and Natural Seismic Events

The mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere. We numerically simulate this coupled system for two application cases: active seismic experiments (ASEs) and passive seismic experiments. A recent ASE (Krishnamoorthy et al., 2018, https://doi.org/10.1002/2018GL077481) observed the infrasonic signals produced by a seismic hammer. To measure the sensitivity of observations to seismic parameters, we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock-solid subsurface. At long range, we investigate the influence of the source by using two focal mechanisms. We found surface waves generate an infrasonic plane head wave in the ASE case of the rock-solid material. For the passive seismic experiments, the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail. Despite some limitations, the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Dynamics of Episodic Magma Injection and Migration at Yellowstone Caldera: Revisiting the 2004-2009 Episode of Caldera Uplift With InSAR and GPS Data

International audienceThe 2004-2009 caldera uplift is the largest instrumentally recorded episode of unrest at Yellowstone caldera. We use GPS and Interferometric Synthetic Aperture Radar (InSAR) time series spanning 2004-2015, with a focus in the aforementioned event to understand the mechanisms of unrest. InSAR data recorded ∼25 and ∼20 cm of uplift at the Sour Creek (SCD) and Mallard Lake (MLD) resurgent domes during 2004-2009, and ∼8 cm of subsidence at the Norris Geyser Basin (NGB) during 2004-2008. The SCD/MLD uplift was followed by subsidence across the caldera floor with a maximum at MLD of ∼1.5-2.5 cm/yr, and no deformation at NGB. The best-fit source models for the 2004-2009 period are two horizontal sills at depths of ∼8.7 and 10.6 km for the caldera source and NGB, respectively, with volume changes of 0.354 and −0.121 km3, and an overpressure of ∼0.1 MPa. The InSAR and GPS time series record exponentially increasing followed by exponentially decreasing uplift between 2004 and 2009, which is indicative of magma injection into the caldera reservoir, with no need for other mechanisms of unrest. However, magma extraction from NGB to the caldera is unable to explain the subsidence coeval with the caldera uplift. Models of magma injection can also explain other episodes of caldera uplift like that in 2014-2015. Distributed sill opening models show that magma is stored across the caldera source with no clear boundary between MLD and SCD. Since the magma overpressure is orders of magnitude below the tensile strength of the encasing rock, historical episodes of unrest like these are very unlikely to trigger an eruption

La télédétection épaule la surveillance de l'éruption de la Soufrière de Saint-Vincent

International audienc

Rupture process of the Oklahoma Mw5.7 Pawnee earthquake from Sentinel-1 InSAR and seismological data

Accepted for publication in Seismological Research Letters.Since 2009, Oklahoma has experienced a sore in induced seismicity, a side effect of extensive saltwater injection into subsurface sedimentary rocks. The seismic hazard entailed by these regional-scale injection operations is however difficult to assess. The September 3, 2016, Mw5.7 Pawnee earthquake is the largest since the increase of seismic activity. The event was preceded by a mb3.2 foreshock two days before, and changes in injection rates have been reported on wastewater disposal wells located less than 10km from the epicenter, suggesting that the earthquake may have been induced. Using Sentinel-1 spaceborne interferometric synthetic aperture radar, we unambiguously show that the earthquake produced peak-to-peak line-of-sight displacement of 3 cm at the surface. Kinematic inversion of geodetic and seismological data shows that the main seismic rupture occurred between 4 and 9km depth, over a length of 8km, with slip reaching at least 40cm. The causative fault is entirely buried within the Precambrian basement, i.e. well beneath the Paleozoic sedimentary pile where injection is taking place. Potentially seismogenic faults in the basement of Oklahoma being poorly known, the risk of Mw≥6 events triggered by fluid injection remains an open question

L' apport de la géodésie spatiale dans la compréhension du processus de rifting magmatique (l'exemple de l'épisode en cours en Afar Ethiopien (2005-2009))

L'épisode de rifting en cours en Afar Ethiopien, initié en Septembre 2005, est étudié à l'aide de l'interférométrie radar (InSAR), et de la corrélation sub-pixel d'images optiques et radar. Un traitement en série temporelle de ces données géodésiques permet de séparer les événements discrets et les déformations transitoires lentes. Les intrusions magmatiques sont isolées, et le champ de déformation de surface est inversé pour déterminer les caractéristiques géométriques des dikes. L'interaction entre dikes est étudiée à l'aide d'un calcul des variations de contraintes normales statiques sur le plan vertical du dike. Des relations d'échelle sont déduites, et leurs implications mécaniques sont discutées. La présence d'un réservoir sub-crustal d'alimentation, situé au centre du segment magmatique, est mise en évidence. Des déformations transitoires, causées par des cycles de remplissage/vidage de ce réservoir, sont suivies au cours du temps. Un modèle synthétique permettant d'expliquer la cyclicité de l'activité magmato-tectonique sur différentes échelles de temps, de l'heure à la centaine d'années, est introduit. Ce modèle prend en compte la stratification rhéologique de la croûte, la dynamique de recharge du système magmatique central et de mise en place des dikes, et la variation d'épaisseur crustale le long de l'axe du rift. Il intègre aussi les informations issues d'observations effectuées lors de crises de rifting précédentes en Afar et en IslandePARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF