Methane (CH4) emissions have to be reduced to reach the Paris Agreement objectives. Modeling approaches assimilating observations are expected to verify the effectiveness of mitigation policies by monitoring sectoral and regional emission changes based on atmospheric observations. These “top-down” approaches are appropriate to estimate CH4 net flux at the surface; however, they have critical weak points: an incomplete prior knowledge of CH4 natural emissions, and difficulties in disentangling overlapping sources from different sectors. The main natural sources of CH4 are inland water emissions: wetlands, peatlands, lakes, ponds… While global wetland emissions gridded products exist, none are available for other inland water systems, which are thus missing in the prior description of emissions forcing top-down approaches. Global estimates of inland water systems remain not consistent in terms of localization and magnitude. Thus, dynamical maps of these areas and their emissions based on same data sets, are necessary to ensure consistency and reduce uncertainties in CH4 emission estimates. 3D top-down approaches retrieving CH4 emissions are based on total CH4 observations only, at surface stations or from remote sensing, and solve for net fluxes at the surface or few individual sectors. However, CH4 observations are not sufficient to properly distinguished between sectors. Isotopic or co-emitted species such as ethane for oil and gas emissions, or carbon monoxide for biomass burning, could help better discriminating the emissions from different sectors and their trend. For this, the project coordinator’s team has newly developed an inverse system (CIF-LMDz-SACs) that integrates isotopic observations to constrain CH4 emissions. The AMB-M3 project aims at 1) producing the first consistent gridded product of CH4 emissions from wetlands, peatlands and lakes to be used for CH4 sources analysis and as input to global top-down models, and 2) discriminating CH4 sources by improving the capabilities of an inverse systems. In the first work package we will develop dynamical and consistent gridded CH4-centric inland water maps including information on vegetation and soil types (carbon content), over 1995-2020 based on the GIEMS-2 inundated data set. GIEMS-2, covering already 1995-2015, provides inundated extent and dynamics under dense vegetation, produces consistent surface water in semi-arid regions and accounts for satellite inter-calibration issues. Then CH4 emissions based on this new product will be estimated by upscaling density fluxes from the literature. Developments on CH4 emissions from wetlands and northern peatlands have been done in different versions of the ORCHIDEE land surface model. For the project, they will be integrated into the trunk version of the ORCHIDEE model to better simulate CH4 emissions and compared to previous estimations. The second work package will demonstrate the potential of adding ethane and carbon monoxide within the CIF-LMDz-SACs surface data constrained global inversions. Analyses will be performed to optimally combine different tracer constraints from both surface and satellite observations to take advantage of all available observations for regional analysis. Finally, AMB-M3 project will provide new estimates of CH4 sources and sinks at the global and regional scales over 2010-2020 based on up-to-date bottom-up (ORCHIDEE) estimates and top-down modelling system.

Almost 2/3 of Earth's surface is covered by oceanic crust formed at mid-ocean ridges where >70% of the total magma flux is concentrated. In the last decades it has been shown that the magmatic system, which has long been seen as a melt-dominated system, is rather mushy: magmatic but with a high crystal fraction. This modifies the expected thermal regime, the modes of melt migration, and the igneous processes that give rise to the crust by differentiation and magma emplacement. Despite tremendous progress made over the last decades by a multidisciplinary marine geoscience community, our understanding of the oceanic magma plumbing architecture and of the related igneous processes at both fast- and slow-spreading ridges still needs to be refined and quantified. More specifically, the modes of differentiation that have been considered during decades to be governed by fractional crystallization (operating in crystal-poor mediums) are now revisited, and a yet poorly constrained reactive porous flow process is now widely proposed. The objective of MUSH-OCEAN is to make a breakthrough in our understanding of oceanic magmatic systems. With MUSH-OCEAN we will provide brand new constraints on 1/ the temporal (e.g., lifespan), spatial, and thermal relations between magma (s.s.) bodies (with 40 % crystals, thus not mobilizable), 2/ the kinematics of melt collection and migration in mushy reservoirs, and 3/ the igneous processes that govern mush evolution, and thus the overall differentiation of oceanic igneous reservoirs (reactive porous flow). Finally, beyond allowing a major advance in our understanding of oceanic magmatic systems (>2/3 of magmatism on Earth), the understanding of the processes governing the evolution of magmatic mushes will allow a better understanding of the majority of igneous systems in other geodynamic contexts since these crystal-rich mediums seem to be dominant in general.

Earthquake occurs at the end of the seismic cycle. During a long time, the plate tectonics increase the stress loading along the plate boundaries, where mega-subduction earthquake eventually happen. Today, thanks to permanent GPS stations installed on subduction margins, we can measure the deformation of the crust associated with the subduction interface loading. This observation can be used to estimate in advance a crucial parameter of the earthquake in preparation: the stress drop. Knowing in advance the distribution of one of the two important parameters controlling the rupture enhances greatly the predictability of the future earthquake. By carefully evaluating the other parameters (the friction parameters), it is possible to compute future rupture scenarios, which can help to mitigate tsunami and strong-motion hazards. This new technique has been recently developed for the Nankai subduction zone, in Japan. However, a real earthquake did not validate the prediction technique. This is the first objective of this project: we need to apply the same technique to a monitored subduction zone where an earthquake occurred, to serve as a blind test. We will then compare the prevision made using only interseismic studies with the actual rupture. The discrepancies will be studied in order to improve the anticipation quality. This closely related to segmentation issues. What is responsible for the apparent segmentation of subduction zones? Can segmentation change over several seismic cycles? Since our goal is to be able to determine reliably what will be the maximum extent of the future rupture, we need to study very large earthquakes, which occurred in sufficiently instrumented regions before the earthquake. There are two equivalent places in the world where we can develop this project: Japan, with the 2011 Mw9.0 Tohoku earthquake, and Chile, with the 2010 Mw8.8 Maule earthquake. The method was initially developed for the Nankai trough, and we have started the study of Tohoku earthquake recently, but Chile seems a better target for this initial part of the project, since ENS team has been working on Chile for years now, and have a stronger expertise than for Japan needed to understand the limitations of the modelling. Of course, developments for Chile will have a strong impact in Japan, and are likely to be applied there too. The final task will be to elaborate scenarios for identified gaps close to rupture in Chile, and in Japan. Around the promising hopes of this approach, there are limitations that we want to investigate deeply. A second objective of this project is to model more precisely the interseismic deformation, and the corresponding stress accumulation on the slab. So far, simplified crustal models, and purely elastic behaviour are used to constrain the slip-deficit distribution. The elastic hypothesis is certainly valid for crustal behaviour at the time of the earthquake, but is it still a good hypothesis when looking at the long time interseismic loading? A related task is to investigate the role of spatial heterogeneities of friction at small scale on both earthquake preparation phase and the rupture. What is the meaning of the so-called plate-coupling rate? Are there different kinds of barriers? Can we locate barriers as well as asperities? There are several points we want to investigate which could improve our fundamental understanding of the mechanical processes leading to megathrust rupture. Finally, the project will contribute to one of the great challenge of modern seismology: rupture dynamic inversion. This technique is not well developed due to several limitations. We propose to improve the method. We will modify the dynamic inversion algorithm to take advantage of the interseismic information. Introducing a realistic a priori stress drop distribution will reduce the number of inverted parameters and increase the reliability of the solutions. Here again, both Tohoku and Maule earthquakes are good candidates.

The understanding of the coupled thermo-hydro-mechanical behaviour of fault zones in naturally fractured reservoirs is of fundamental importance for a variety of societal and economic reasons, such as the sustainable energy transition for the safe use of natural resources (energy storage, nuclear waste disposal or geothermal energy). The overall objective of this project is to better understand the physical processes resulting from a thermal and hydric load on an existing, identified and characterized fault zone. The idea here is to carry out a thermally controlled in situ fluid injection experiment in one of the faults accessible from the Tournemire underground research laboratory (URL). A heating system will be installed around the injection area and enable a precise and controlled incremental increase of the thermal load. In addition, an important monitoring system will be installed to measure the seismic and aseismic events induced either by thermal or by hydraulic loading. The monitoring system will be composed of acoustic and broadband sensors that will measure low to medium magnitude events. Furthermore, it is also planned to install a fibre optic network to measure temperature and displacement in a distributed manner in the investigation area. The active seismic methods will be deployed before and after the experiment to determine the structural network but also to detect the appearance of new structures triggered from the hydro-thermal pressurisation of the fault. A series of laboratory experiments will be conducted to understand the chemical and structural evolution occurring within the fault zones during the thermal and hydraulic loading. Experiments in climatic chambers exposing the samples to the same heat treatment as that of the in situ experiment will be carried out in order to compare the mineralogical composition evolution of the samples with those taken from the field investigated zone. Finally, a rock mechanical study, from the microscopic to the centimeteric scale with monitoring of the acoustic properties will be carried out. This study will include experiments from Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDS) allowing the identification of the micro-scale mechanisms of deformation localization to which it is planned to add an acoustic measurement system. In order to study the evolution of mechanical behaviour as a function of scale, experiments in triaxial press, again with acoustic monitoring, are planned.