Joint Inversion of Coseismic and Early Postseismic Slip to Optimize the Information Content in Geodetic Data: Application to the 2009 M_w 6.3 L'Aquila Earthquake, Central Italy

When analyzing the rupture of a large earthquake, geodetic data are often critical. These data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. As a consequence, many studies analyze the coseismic rupture with data that also include one or more days of early postseismic deformation. Here, we invert simultaneously for the coseismic and postseismic slip with the condition that the sum of the two models remains compatible with data covering the two slip episodes. We validate the benefits of this approach with a toy model and an application to the 2009 M_w 6.3 L'Aquila earthquake, using a Bayesian approach and accounting for epistemic uncertainties. For the L'Aquila earthquake, we find that if early postseismic deformation is not an explicitly acknowledged coseismic signal, coseismic slip models may overestimate the peak amplitude while long‐term postseismic models may largely underestimate the total postseismic slip amplitude. This example illustrates how the proposed approach could improve our comprehension of the seismic cycle, fault frictional properties, and the spatial and temporal relationship between seismic rupture, afterslip, and aftershocks

Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE.

We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): "Surfaces and Near-surface Exospheres of the Satellites, dust and rings"

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

Mesures InSAR et modélisation de faibles déformations d'origine anthropique (lac Mead, USA) ou tectonique (faille de Haiyuan, Chine)

I used radar interferometry to measure and model the Earth surface deformation of small amplitude ($<$cm). InSAR has proven to be a powerful tool to mapp surface deformation with sub-centimetric accuracy. However, interferograms correction from atmospheric delays is often required to reach such an accuracy. A large part of my work has thus been dedicated to this task. The first study area is the deformation around the Lake Mead (Nevada, USA). This artificial lake has been filled with water in 1935. An earlier study, based on leveling measurements, has shown that the load associated with lake impoundement induced a subsidence of 17 centimeters. This relaxation process has been argued as analogous to the postglacial rebound, but at a smaller spatial scale and with a much lower viscous relaxation time scale. To quantify the deformation and thus constrain the crust and mantle rheological parameters in the lake area, we analyze multiple interferograms (241) based on 43 ERS images acquired between 1992 and 2001. Corrected interferograms are then inverted to solve for the time series of ground motion in the lake Mead area. We obtain a time series of the deformation in the lake Mead area with a millimetric accuracy. The deformation is non linear in time and spreads over a large spatial scale. The deformation model allows to constrain the rheology in the lake Mead area. The model takes into account the loading history of the lake since 1935. We show that a simple elastic response with parameters constrained by seismic wave propagation does not explain the amplitude and spatial wavelength of the observed motion. To fit the data, a low viscosity (around 10$^{18}$ Pa.s) in the mantle below a 30 km thick elastic layer is required. In a second study, I have studied the interseismic displacement across the Haiyuan fault. This fault is one of the major left-lateral faults that accommodates part of the deformation due to India-Asia collision at the north-eastern edge of the Tibetan plateau. Our objective is to better constrain the present mechanical behavior of this fault system, at the origin of two M$\sim$8 earthquakes in 1920 and 1927 and along which a seismic gap with high potential seismic hazard has been identified. We focus on the Tianzhu seismic gap segment, along which the long-term slip rate has been estimated to 12 (+/-)4 mm/yr from neotectonic studies (Lasserre et al., 1999). We analyze ERS SAR data from two tracks along descending orbits between longitudes 102.6\degresE and 105.3\degresE and latitudes 36\degresN and 38\degresN. The results between both independent tracks are very consistent. A screw dislocation model in an elastic half space indicates an average fault-parallel velocity of 6.5 $\pm$mm/yr and a very small apparent locking depth of about 1.7 km. Superficial creep or a compliant zone around the fault could also explain this low value.Cette thèse porte sur la mesure par interférométrie radar (InSAR), et la modéli\-sation de faibles déformations, de moyennes à grandes longueurs d'onde spatiale. L'InSAR s'est révélée être, depuis quelques années, un outil performant pour mesurer de petites déformations, à la condition, notamment, de corriger suffisamment les délais atmosphériques perturbant le signal radar et la mesure de la déformation. Une partie de cette thèse montre des développements méthodologiques spécifiques effectués afin d'obtenir une mesure subcentimétrique effective sur deux chantiers d'application. Les deux études présentées dans ce manuscrit montrent deux approches différentes, liées aux contraintes matérielles (nombre d'images/nombre d'interférogrammes calculables) et au type de déformation recherché. Dans un premier temps, j'ai mesuré la déformation autour du lac Mead (Nevada, USA). Cette déformation est due aux fluctuations du niveau d'eau du lac depuis sa mise en eau en 1935. Pour quantifier cette déformation, et contraindre les paramètres visco-élastiques de la lithosphère dans la région du lac Mead, j'ai analysé 241 interférogrammes calculés avec des images acquises par les satellites ERS entre 1992 et 2002. L'inversion des interférogrammes corrigés des délais orbitaux et tropostatiques a permis d'établir la série temporelle du déplacement du sol sur ces 10 années. Des modèles directs montrent qu'une simple réponse élastique n'explique ni l'amplitude de la déformation, ni la longueur d'onde spatiale de la déformation. Il semble donc qu'il soit nécessaire de prendre en compte la viscosité du manteau pour retrouver la déformation. Un modèle simple, concordant avec une étude précédente \citep{kaufmann00a}, constitué d'une croûte élastique d'environ 30 km et d'un manteau supérieur présentant une viscosité de 10$^{18}$ Pa.s, explique bien les données. Dans un deuxième temps, je me suis intéressé à la déformation intersismique à travers la faille de Haiyuan (Gansu, Chine), située au nord est du plateau tibétain. Il s'agit d'une des failles décrochantes sénestres majeures qui accommode en partie la collision Inde-Asie. L'objectif était de mieux contraindre le comportement mécanique de ce système de faille, à l'origine de deux séismes de M$\sim$8 au cours du XXième siècle. Je me suis focalisé sur un segment particulier de la faille appelé ''la lacune sismique de Tianzhu'', dont la vitesse long-terme à été estimée à 12 $\pm$4 mm/an à partir d'études neotectoniques. J'ai analysé des données radar ERS acquises sur deux orbites descendantes le long de la lacune. Une fois les interférogrammes corrigés de l'erreur résiduelle orbitale et du délai tropostatique, ils ont été sommés afin d'obtenir une carte de vitesse moyenne dans la zone de faille (déterminée par les images ERS disponibles, i.e. 1993-1998). Un modèle classique de dislocation dans un demi-espace élastique homogène indique une vitesse instantanée de 6.5 $\pm$3 mm/an, mais aussi une profondeur de blocage faible autour de 1.7 km. Cependant, ce résultat peut aussi être expliqué par d'autres modèles incluant une zone d'endommagement autour de la faille ou du glissement superficiel

In Situ Exploration of the Giant Planets and an Entry Probe Concept for Saturn

ESA 2013 call for White Papers for the definition of L2 and L3 Missions in the ESA science programme, 201

Fault Interactions and Synchronization: Insight from the 1936-1997 NE Lut, Iran, Earthquake Sequence

International audienc

Expérimenter les humanités numériques : Des outils individuels aux projets collectifs

Univers en perpétuelle expansion et au foisonnement chaotique, Internet offre un nombre incalculable d’outils, dont l’exploration paraît parfois hors de portée. Dans le paysage des sciences humaines, les blogs, les logiciels bibliographiques, les bases de données, les éditions en ligne et les wikis, tous ces objets qui éveillaient notre curiosité il y a une décennie, sont devenus aussi anodins qu’omniprésents. Mais comment bien s’en servir ? Les appréhensions face à ces outils – et leur simple mais robuste méconnaissance – sont encore largement répandues. Or on ne peut plus ignorer leur intérêt, voire leur nécessité, et les chercheurs qui s’y essaient ne savent souvent pas par quel bout attraper ces logiciels nouveaux. C’est à cela que cet ouvrage veut les aider, de façon simple et précise, et il entend le faire sans en cacher les difficultés, mais sans dissimuler non plus qu’elles sont désormais connues, donc surmontables, et que, dans la majorité des cas, le résultat vaut tous les efforts à consentir