Although shakemaps are of great interest for large-magnitude earthquakes where the ground motion is mainly controlled by the rupture on the fault, their relevance for moderate-size events is still questionable. So far, the implemented ground-motion prediction does not have the necessary spatial resolution to account for the real impact of the earthquake, because shakemaps use only first-order parameters that are not relevant for the fine city or building scales. This results in their poor efficiency in areas close to moderate earthquakes and/or located on deep sedimentary layers prone to complex site effects. This project aims at improving the reliability and the spatial resolution of the shakemaps and at developing damage maps to predict the impact of an earthquake anywhere, including in complex geological environments and in the lack of seismological data. Our methodology is targeted on rapid and low-cost estimates, but still keeping track of physics-based approaches. We take advantage of satellite imagery in France to develop an innovative method for retrieving sediment thicknesses and predicting sediment resonance periods based on the mapping of subsidence rates in alluvial and urbanized valleys from InSAR data. The collected parameters are compared to observations: earthquake recordings from French seismic stations, from low-cost seismometers hosted by citizens, contemporary and historical macroseismic intensities. The comparison is performed by artificial intelligence to develop a new estimator of the aggravation of the ground motion at fine scale in sedimentary valleys and their periphery. The combination of the high-resolution shakemaps with an innovative damage prediction model will allow to get the damage maps at building scale.

Dating hydrothermal mineralization is difficult because most chronometers are commonly reset in open system. Although monazite is rare in hydrothermal deposits, it is very attractive to date mineralization because it has a very robust isotopic system (U-Th-Pb) that retains the age of its precipitation. In presence of successive fluid circulations, monazite (re)crystallizes sporadically. Growth episodes are identifiable from zoning in trace elements composition (REE+Y, Th, U and Pb). Using in-situ high resolution techniques (spot size ~ 5µm), it is possible to date these distinct domains and to obtain the age of the successive mineralization stages. In monazite taken from Alpine clefts (Central Alps), preliminary SIMS U-Th-Pb dating gave very promising results. Results show that Miocene monazite can be dated with a resolution of 0.2 Ma. Within a single grain, it is possible to distinguish episodic growth stages separated by an interval <2Ma. Furthermore, monazite is zoned with extreme trace elements fractionation (Th/U up to 600), which remains to be understood. The aim of this project is to investigate the potential of monazite as chronometer and geochemical tracer of fluid mineralization via detailed characterization of natural samples and hydrothermal experiments. The objectives are two-fold : (1) Obtaining monazite growth ages and growth duration for different areas of the Alps and to link them with the local deformation and exhumation history, (2) trying to understand chemical and isotopic behaviour of the REE+Y, Th and U during monazite/fluid interaction. Project achievement will require a pluridisciplinar approach combining mineralogy, experimental petrology, geochronology and structural geology. For the experimental part (ISTerre, Grenoble), we expect to perform 32 experiments in cold-seal vessels in order to evaluate the role of monazite composition, T, fO2 and fluid speciation on the trace elements behaviour. For the natural case study, we dispose of large hydrothermal monazite crystals taken from different parts of the Alps. Identification of experimental and natural phases requires use of advanced and expensive analytical techniques, including XRD, EMP, SEM, TEM, FIB, LA-ICP-MS, SIMS and fluid inclusions analyses (GET, Toulouse). High-resolution Th-Pb isotopic age dating of cleft monazites will be obtained using LA-ICP-MS (Laboratoire Magmas-Volcans, Clermont-Ferrand). For the realization of the project, we demand for the funding of a PhD student. .

In recent years, multi-step nucleation pathways involving the formation of pre-nucleation clusters, nanocrystalline and amorphous precursors, have been reported for a wide variety of inorganic and organic phases, including natural and engineered cements. A paradigmatic example is that of the CaCO3 system, which has been shown to form in some cases via an amorphous calcium carbonate (ACC) precursor, formed itself via the aggregation of CaCO3 prenucleation clusters. In a very recent study we have shown that C-S-H, the main component of cement, is also formed in solution via amorphous precursor clusters. This amorphous precursor pathway offers a ‘cheaper’ alternative route through the free energy landscape, due to the lower interfacial energies of the intermediate phases, which considerably reduce the nucleation barrier. In addition, these pathways probably present evolutionary advantages for biominerals, due to the easiness by which the organisms can mold these precursor phases into intricate shapes. However, and in spite of the abundant literature aimed at understanding the amorphous precursor pathway and its thermodynamics and kinetics characteristics, many open questions remain unanswered, blocking the development of effective strategies for the synthesis of novel biomimetic materials and of new additives to control the crystallization process. This project aims to build some bridges between the researches performed in the field of ‘natural cements’, bringing this knowledge to the study of nucleation of ‘engineered cements’. The key questions that still need to be resolved can be divided in two categories: (a) What is the structure of these clusters, and how is it modified in the presence of additives? Is the initial structure a signature of the final polymorph? And (b) what are the molecular mechanisms of stabilization of the amorphous precursors? What is the role of water? Here, we plan to provide answers to these questions by using a combination of state-of-the-art scattering and spectroscopy techniques combined with detailed chemical speciation. Task 1 of this project will deal with the study of the structure of aqueous (pre-nucleation) clusters. Recent advances in X-ray scattering and detection devices have made it possible now to perform experiments in very diluted conditions, providing for the first time the possibility to describe the internal structure of CaCO3 pre-nucleation clusters using the pair distribution function method. Small-angle and pair distribution function experiments will be performed as well to characterize the formation conditions and the structure of the precursor phase to C-S-H. All these experiments will be performed under controlled chemical conditions, using a titration setup and synchrotron radiation. Task 2 includes an original approach to probe the atomistic dynamics and the stability against crystallization of amorphous precursors. Complementary techniques such as X-ray photon Correlation Spectroscopy and Inelastic Incoherent Neutron Scattering will be used to probe the atomistic dynamics of ions and water, respectively. These techniques will serve to test the long-standing simulation-based hypothesis that water acts as a stabilizer of the amorphous structure in the case of ACC. Systematic studies of the microscopic dynamics of ACC and of C-S-H amorphous precursors in the presence of different additives, and at different hydration states, will be performed. The results of this research will have a large impact for (i) the understanding of how additives control the nucleation of naturally-occurring cements, such as ACC in biominerals, and (ii) the improved design of additives to control crystallization of engineered cements, of which C-S-H is the main component. This research will also impact other applications where a control on the crystallization kinetics is desired, such as restoration of cultural heritage, CO2 sequestration via mineral trapping or the prevention of scale formation.

The decline of Arctic sea ice extent is one of the most spectacular signatures of global warming, and studies converge to show that this decline has been accelerating over the last 4 decades, with a rate that was not anticipated by forecasting models. In order to improve these models, relying on comprehensive and accurate field data is essential. While sea ice extent and concentration are accurately monitored from microwave imagery, we are still lacking an accurate and comprehensive measure of its thickness. In addition, models could benefit from including other observables related to the ability of the ice cover to resist cracking and to heal/reform when cracking occurs. The ICEWAVEGUIDE project introduces a methodology based on seismic waves propagation to meet these needs, and aims at completing current knowledge so far acquired mostly from Radar and Sonar data. Based on continuous, passive recordings of seismic ambient noise at an array of geophones, the ICEWAVEGUIDE project will demonstrate that propagation of leaky seismic waves guided in the thickness of the ice can be measured. Guided waves being sensitive to the geometrical and mechanical properties of the waveguide, the measures will be inverted to recover important markers of ice mechanical resistance, such as thickness, elastic properties and damage level. This new methodology was successfully tested on data acquired in a lab-scale experiment. The experiment consisted in leaving a water tank in a cold room so as to grow an ice layer at its surface. While its thickness was increasing, ultrasonic guided waves were generated in the ice with a piezoelectric source, and measures were subsequently inverted to monitor the thickness and mechanical properties of the ice. The goal of the proposal is to extend this proof of concept on actual geophysical data acquired on a frozen lake in Svalbard (Norway) during winter. The project will be decomposed in 5 packages: data acquisition at Vallunden Lake (WP1), data processing (WP2), forward modelling (WP3), data inversion (WP4), and identification of ice resilience markers (WP5).

The main objective of the Project is to explore the possibility to use seismic wave?elds emerging from the correlation of long recordings (a.k.a. seismic interferometry) to probe the Earth’s deep interior. In practice, we want to build and mine a new robust dataset of seismic signals that are complementary to earthquake data, for improved deep-mantle and core imaging. The Project will focus on the core-mantle boundary (CMB) region. Two methodological approaches will be explored on a global scale: microseism-based and coda-based correlations. On the one hand, the correlation of microseism signals with the aid of excitation models will be used to constrain the structure of the velocity of the entire lower mantle. On the other hand, the correlation of the reverberated coda of large earthquakes will be used to question the existence of a stratified layer at the top of the outer core. The geodynamics of these two targets are still an on-going debate, mainly due to incomplete direct observables. TerraCorr will pave the way towards a much broader use of continuous seismic signals to improve our understanding of the Earth’s history and its present dynamics.