ERC FUNDED PROJECTS

Despite the dramatic impact of earthquakes, the physics of their onset and the short-term behavior of fault are still poorly understood. Using existing high quality seismic observations, we propose to develop a novel functional imaging of the brittle crust to clarify not only structural properties but also the dynamics of faults. We will analyze spatio-temporal changes of elastic properties around fault zones to highlight the interplay between changes in the host rocks and fault slip. Imaging the damage structure around faults and its evolution requires new seismological methods. With novel methods to image the highly heterogeneous fault regions, we will provide multi-scale descriptions of fault zones, including their laterally variable thicknesses and depth dependence. In parallel we will image temporal changes of seismic velocities and scattering strength. External natural forcing terms (e.g. tides, seasonal hydrologic loadings) will be modeled to isolate the signals of tectonic origin. This will also allow us to monitor the evolving seismic susceptibility, i.e. a measure of the proximity to a critical state of failure. Improved earthquake detection techniques using ‘deep machine learning’ methods will facilitate tracking the evolution of rock damage. The imaging and monitoring will provide time-lapse images of elastic moduli, susceptibility and seismicity. The observed short-time changes of the materials will be included in slip initiation models coupling the weakening of both the friction and the damaged host rocks. Laboratory experiments will shed light on the transition of behavior from granular (shallow fault core) to cohesive (distant host rock) materials. Our initial data cover two well-studied fault regions of high earthquake probability (Southern California and the Marmara region, Turkey) and an area of induced seismicity (Groningen). The derived results and new versatile imaging and monitoring techniques can have fundamental social and economic impacts.

2 434 743 €

Start date: 2017-10-01, End date: 2022-09-30

The initial conditions of the Earth and other terrestrial planets were set 4.5 Gy ago during their accretion from the solar nebula and their concomitant differentiation into an iron-rich core and a silicate mantle. Accretion in the solar system went through several different dynamical phases involving increasingly energetic and catastrophic impacts and collisions. The last phase of accretion, in which most of the Earth mass was accreted, involved extremely energetic collisions between already differentiated planetary embryos (1000 km size), which resulted in widespread melting and the formation of magma oceans in which metal and silicates segregated to form the core and mantle. Geochemical data provide critical information on the timing of accretion and the prevailing physical conditions, but it is far from a trivial task to interpret the geochemical data in terms of physical conditions and processes. I propose here a fluid dynamics oriented study of metal-silicate interactions and differentiation following planetary impacts, based in part on fluid dynamics laboratory experiments. The aim is to answer critical questions pertaining to the dynamics of metal-silicate segregation and interactions during each core-formation events, before developing parameterized models of metal-silicate mass and heat exchange, which will then be incorporated in geochemical models of the terrestrial planets formation and differentiation. The expected outcomes are a better understanding of the physics of metal-silicate segregation and core-mantle differentiation, as well as improved geochemical constraints on the timing and physical conditions of the terrestrial planets formation.

1 258 750 €

Start date: 2017-04-01, End date: 2022-03-31

For more than 30 years, seismologists have used seismic waves to produce 3D images of the structure of the Earth. Despite many successes, a number of key questions still remain, which are of the uttermost importance to understand plate tectonics. What is the nature of the Lithosphere-Asthenosphere Boundary? What is the structure and history of the continental lithosphere? The problem is that different seismic observables sample the Earth at different scales; they have different sensitivity to structure, and are usually interpreted separately. Images obtained from short period converted and reflected body waves see sharp discontinuities, and are interpreted in terms of thermo-chemical stratification, whereas seismic models constructed from long period seismograms depict a smooth and anisotropic upper mantle, and are usually interpreted in terms of mantle flow. However, sharp discontinuities may also produce effective anisotropy at large scales, and only a joint interpretation of different frequency bands can allow to fully localizing the patterns of deformation in the mantle. The proposed work consists in developing and applying an entirely new approach to geophysical data interpretation, where different data types sampling the Earth at different scales are jointly embraced into a single Bayesian procedure. This proposal focuses on theoretical, algorithmic and computational advances needed for a new generation of tomographic models. We will use the large amount of data available in North-America (surface wave measurements, scattered body waves, SKS splitting measurements) to produce a multiscale model under North-America, depicting both discontinuities and anisotropy. This will allow us to answer some crucial questions about the structure and evolution of Earth. We will also produce a first fully Bayesian global Earth model by jointly inverting normal modes, surface and body wave observations.

1 498 750 €

Start date: 2017-04-01, End date: 2022-03-31