A detailed source model for the M_w9.0 Tohoku-Oki earthquake reconciling geodesy, seismology, and tsunami records

The 11 March 2011 M_w9.0 Tohoku-Oki earthquake was recorded by an exceptionally large amount of diverse data offering a unique opportunity to investigate the details of this major megathrust rupture. Many studies have taken advantage of the very dense Japanese onland strong motion, broadband, and continuous GPS networks in this sense. But resolution tests and the variability in the proposed solutions have highlighted the difficulty to uniquely resolve the slip distribution from these networks, relatively distant from the source region, and with limited azimuthal coverage. In this context, we present a finite fault slip joint inversion including an extended amount of complementary data (teleseismic, strong motion, high-rate GPS, static GPS, seafloor geodesy, and tsunami records) in an attempt to reconcile them into a single better resolved model. The inversion reveals a patchy slip distribution with large slip (up to 64 m) mostly located updip of the hypocenter and near the trench. We observe that most slip is imaged in a region where almost no earthquake was recorded before the main shock and around which intense interplate seismicity is observed afterward. At a smaller scale, the largest slip pattern is imaged just updip of an important normal fault coseismically activated. This normal fault has been shown to be the mark of very low dynamic friction allowing extremely large slip to propagate up to the free surface. The spatial relationship between this normal fault and our slip distribution strengthens its key role in the rupture process of the Tohoku-Oki earthquake

Finite-Difference Modeling of Acoustic and Gravity Wave Propagation in Mars Atmosphere: Application to Infrasounds Emitted by Meteor Impacts

The propagation of acoustic and gravity waves in planetary atmospheres is strongly dependent on both wind conditions and attenuation properties. This study presents a finite-difference modeling tool tailored for acoustic-gravity wave applications that takes into account the effect of background winds, attenuation phenomena (including relaxation effects specific to carbon dioxide atmospheres) and wave amplification by exponential density decrease with height. The simulation tool is implemented in 2D Cartesian coordinates and first validated by comparison with analytical solutions for benchmark problems. It is then applied to surface explosions simulating meteor impacts on Mars in various Martian atmospheric conditions inferred from global climate models. The acoustic wave travel times are validated by comparison with 2D ray tracing in a windy atmosphere. Our simulations predict that acoustic waves generated by impacts can refract back to the surface on wind ducts at high altitude. In addition, due to the strong nighttime near-surface temperature gradient on Mars, the acoustic waves are trapped in a waveguide close to the surface, which allows a night-side detection of impacts at large distances in Mars plains. Such theoretical predictions are directly applicable to future measurements by the INSIGHT NASA Discovery mission

Seismic constraints from a Mars impact experiment using InSight and Perseverance

NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

Atmospheric Science with InSight

International audienceIn November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP3), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous in situ missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSight’s sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both “noise” to be decorrelated from the seismic signal and “signal” to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Le rôle des traces écrites en sciences au cycle 3

Language development is a critical issue of the investigative approach in science. Writings are very important in science teaching. It was interesting to verify if writings influence the change of ideas of pupils and their learnings. Two types of approaches were proposed to the pupils : a transmissive approach with a few writings made by the pupils, and an investigative one with more writings in order to determine their role. The results show that the ideas of pupils change with the two types of approach, but scientific concepts are better acquired when pupils are in a research situation. Writings generated by pupils allow a better knowledge anchoring, permitting them to check information by referring to their previous work and to visualise their line of reasoning. Pupils can discuss about these writings, enabling them to progress in their research. Writing impact on learnings is nevertheless difficult to quantify.Un enjeu de la démarche d’investigation en sciences est le développement du langage. Les traces écrites tiennent donc une place importante dans l’enseignement des sciences. J’ai trouvé intéressant d’étudier le rôle de ces traces écrites et de voir si elles permettent une évolution des conceptions des élèves et l’acquisition des concepts scientifiques de manière plus durable. Ainsi, les élèves ont vécu deux types de démarches : une séquence dispensée en transmissif avec peu de traces écrites produites et une autre faite en démarche d’investigation afin de déterminer le rôle des écrits produits au cours de cette démarche. Les résultats de cette étude montrent que les conceptions des élèves évoluent avec les deux types de démarches, mais que les concepts scientifiques sont mieux acquis lorsque les élèves sont placés en situation de recherche. Les traces écrites produites par les élèves permettent un meilleur ancrage du savoir en leur laissant la possibilité de vérifier des informations en se référant à ce qui a été vu en classe et de visualiser le cheminement de leur pensée. Elles sont aussi la source de nombreux échanges entre pairs qui leur permettent d’avancer dans leur réflexion. Cependant, leur impact sur les apprentissages reste difficilement quantifiable

Sismologie ionosphérique (détection et modélisation des ondes ionosphériques postsismiques)

Nous détectons et modélisons les perturbations ionosphériques générées après un séisme ou le passage d'un tsunami. Des ondes acoustiques sont forcées par le passage des ondes de Rayleigh à la surface de la Terre solide, tandis que dans l'océan la propagation d'un tsunami génère des ondes de gravité. Nous confirmons en particulier la détectabilité des ondes de gravité générées par le passage de trois tsunamis transpacifiques récents (Kouriles 2006, Samoa 2009 et Chili 2010) au large de l'archipel d'Hawaï, grâce à un réseau dense de stations GPS (Global Positioning System). Une modélisation complète tridimensionnelle au premier ordre des ondes de Rayleigh atmosphériques et ionosphériques est proposée. Les fluctuations du plasma ionosphérique modélisées nous permettent de reconstruire les perturbations du contenu électronique total (TEC) détecté par GPS. L'influence du champ géomagnétique sur le couplage entre l'atmosphère neutre et l'ionosphère est aussi illustrée en différents endroits du globe et nous étudions l'influence de la géométrie d'observation, afin de mieux caractériser la sensibilité directionnelle de la détection. Nous mettons ainsi en évidence la nécessité d'améliorer notre connaissance de la haute atmosphère et de ses mécanismes physiques, tels que les effets de dissipation thermique et visqueuse, ainsi que le frottement des ions sur les particules neutres. Ces travaux ouvrent des perspectives pour l'observation depuis l'espace des séismes et des tsunamis et pourraient contribuer à terme à la prévention de ces risques naturels.We detect and model the ionospheric perturbations generated after an earthquake or the passage of a tsunami. Acoustic waves are forced by the passage of Rayleigh waves at the Solid Earth surface, while in ocean the tsunami propagation generates gravity waves. In particular, we confirm the detectability of gravity waves generated by the passage of three recent transpacific tsunamis (Kouriles 2006, Samoa 2009 and Chile 2010) offshore the Hawaii archipelago, thanks to a dense network of GPS (Global Positioning System) receivers. A first-order complete three-dimensionnal modeling of Rayleigh-waves induced atmospheric and ionospheric waves is proposed. The modelled ionospheric plasma fluctuations allow the reconstruction of total electron content (TEC) perturbations detected by GPS. The geomagnetic field influence on the coupling between the neutral atmosphere and the ionosphere is also illustrated in various locations of the world and we study the influence of the observation geometry, in order to better characterize the directional sensitivity of the detection. We also highlight the necessity of improving our knowledges about the high atmosphere and about the physical mechanisms involved, as the thermal and viscuous dissipation effects, as much as the drag of ions on the neutral particles. This work opens perspectives for future space-based observations of eathquakes and tsunamis and could contribute to prevent these natural risks.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Detection and modeling of Rayleigh wave induced patterns in the ionosphere

International audienceGlobal Positioning System (GPS) allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events. We describe a method to model the time and space distributions of Rayleigh wave induced total electron content (TEC) patterns detected by a dense GPS array. We highlight the conditions for which a part of the ionospheric pattern can be directly measured, at teleseismic distance and above the epicenter. In particular, a satellite elevation angle lower than 40 degrees is a favorable condition to detect Rayleigh wave induced ionospheric waves. The coupling between the solid Earth and its atmosphere is modeled by computing the normal modes of the solid Earth-atmosphere system. We show the dependency of the coupling efficiency on various atmospheric conditions. By summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake. This shows that a part of the observation is a Rayleigh-induced radiation pattern and therefore characteristic of the seismic rupture. Through atmosphere-ionosphere coupling, we model the ionospheric perturbation. After the description of the local geomagnetic field anisotropic effects, we show how the observation geometry is strongly affecting the radiation pattern. This study deals with the related data for two earthquakes with far-field and near-field observations using the Japanese GPS network GEONET: after the 12 May 2008 Wenchuan earthquake (China) and after the 25 September 2003 Tokachi-Oki earthquake (Japan), respectively. Waveforms and patterns are compared with the observed TEC perturbations, providing a new step toward the use of ionospheric data in seismological applications

Seismo‐Ionospheric Observations, Modeling, and Backprojection of the 2016 Kaikōura Earthquake

International audienceWe processed Global Navigation Satellite System (GNSS) time‐series data to extract total electron content (TEC) perturbations of the ionosphere caused by the Kaikōura earthquake. We used ray‐based modeling to infer which part of the Earth’s surface coupled significant energy from the solid Earth into the atmosphere. We compared modeled TEC data with the observed time‐series data and determined that significant coupling occurred north‐northeast of the initial slip. This work corroborates existing analysis made with geodetic and Interferometric Synthetic Aperture Radar (InSAR) data. The TEC data suggested that the initial rupture coupled some energy into the atmosphere, but later surface displacements ( ∼60  s after the initiation) caused more significant ionospheric perturbations. Using an array of GNSS stations, we were able to track the moveout of the acoustic wave through the ionosphere. We used a method commonly used in seismological studies called backprojection to estimate the location of the source of the TEC perturbation on Earth’s surface. This is the first time that this method has been applied to TEC data, and the results are promising. The backprojection results are slightly shifted in space from the known area of maximum uplift, and we attribute this small discrepancy to the fact that we did not account for horizontal winds in the atmosphere, nor the 3D heterogeneity of the real atmosphere in the travel‐time modeling