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Complex RhEologies in Earth dynamics and industrial Processes

Periodic Reporting for period 2 - CREEP (Complex RhEologies in Earth dynamics and industrial Processes)

Reporting period: 2017-04-01 to 2019-03-31

The word CREEP has multiple meanings, but in the Innovative Training Network CREEP it stands for Complex RhEologies in Earth and industrial Processes. Rheology (from the Greek ρειν, “to flow”) is the study of how a material deforms in response to applied forces. In industry, knowledge of rheology is key for producing high-performance materials. In Earth Sciences, the rheology of rocks controls the dynamics of our planet. Rheology is also critical in many fields of Earth Sciences that have a direct societal impact. Knowledge of how rocks react when stressed and how they heal afterwards is essential to understand faults dynamics and estimate earthquakes and tsunami hazard. This knowledge is also essential to predict and control seismicity associated with energy production activities, to develop clean energy production methods, like geothermics, and to establish safe natural reservoirs for chemical and radioactive waste.

The objective of the CREEP research program is to advance our understanding of the complex rheology of Earth and industrial materials and its consequences for our planet dynamics, from the global deformation to natural or human-induced seismicity, and for industrial uses of rock-like materials. To fulfil this aim, we use a multidisciplinary and multi-scale approach, which associates observations, experiments, and numerical and laboratory modelling in mineral physics, rock mechanics, tectonics, seismology, and geodynamics, spanning a wide range of spatial scales, from the nanoscale to global mantle dynamics.

- structured the collaboration in research and doctoral training between 10 academic centres in Earth Sciences and 11 partner organizations whose activity encompasses a wide range of fundamental studies and industrial applications in the domain of rheology (chemical industries, glass, steel, fuel exploration, high technology SMEs), bringing together in-depth expertise from six European countries.
- provided training to 16 early stage researchers via a structured program of cross-disciplinary collaborative research, specialized short courses, workshops, practical activities, and secondments in the industrial partners. This experience-based training is centred on research projects leading to a PhD, which focus on the rheology of Earth materials and its implications for geodynamic and industrial processes. The research projects cover a large spectra of applications, which include the study of the deformation of the Earth surface (earthquakes) and interior, geothermal or petroleum exploration, establishment of safe reservoirs for chemical and radioactive waste disposal, and industrial processes.
WP1. Experimental characterization of rheology
We characterized, using laboratory experiments, the rheology of key materials for the Earth dynamics and for industrial applications (exploration, waste storage, or glass industry). Most notable results to date are:
- new data on transient creep behaviour of olivine-rich rocks showing strain hardening, but no associated microstructural evolution;
- successful use of noise interferometry to image the exploration-induced deformation in a gas field;
- new constraints on the role of deformation on the storage properties of rock-salt;
- new data the mechanical behaviour of fault rocks during earthquakes and a physical model explaining this behavior;
- data on the mechanical behaviour of industrial glasses at high pressure and temperature;
- constraints on the effect of pressure and temperature on fault healing processes and on the brittle-ductile transition.

WP2. Laboratory modelling of complex rheologies
We developed physical models and define new analog materials to study the effect of complex rheologies of Earth materials on the planet dynamics. Main results to date are:
- a global database of seafloor roughness and seismogenic behaviour in subduction zones and a model relating both quantities;
- scaling laws for the dynamics of free subduction;
- new constraints on the rheology and dynamics of bi-phase systems with high solid fractions.

WP3. Numerical modelling of complex rheologies
We developed numerical models for studying the effects of history-dependent rheologies and of complex feedbacks on the deformation at various scales, from mantle convection and plate tectonics to hydrothermal fields. Main results to date are:
- establishment of an effective parameterisation of the mechanical anisotropy due to strain-induced orientation of olivine crystals in the mantle;
- extension of the capabilities of the code LaMEM, allowing the predict the 3D failure patterns that may be produced by fluid injection in a reservoir;
- constraints on the physical properties of the Large Low Shear Velocity provinces in the deep mantle based on convection models with a time-evolving rheology;
- numerical models of the growth of a transform fault by alternated aseismic creep and propagation of dynamic rupture.

WP4. Seismological investigations of deformation and rheology
We developed and/or perfected seismological methods to indirectly study the deformation of the Earth. Most notable results to date are:
- seismic evidence of flow-induced anisotropy in the lowermost mantle beneath the central Atlantic;
- a modelllng workflow to predict the seismic anisotropy of salt structures in sedimentary basins;
- methods based on the analysis of seismic anisotropy to study fracture compliance.

WP.5 Training
This WP comprised a personalized follow-up of each ESRs career development plansand network-wide activities.The 4 workshops and 4 short-courses planned were successfully organized (cf. ITN CREEP website). All ESRs performed at least one academic and one industrial secondment.

WP6. Public engagement
The CREEP ESRs attended >30 international conferences, where they presented 41 orals and 47 posters, winning 3 Outstanding Student Presentation Awards. They published 16 articles in 1st-level journals in Earth Sciences. Other articles are submitted or in preparation. They also led or participated to a range of outreach activities. They prepared movies (Special Award of the Honorary Committee of the “On the Rocks” video contest) and webpages presenting their work, visited schools and received school pupils in the labs, created blogs sharing their experience, contributed with articles to the EGU and to the AGU websites, and created and presented experiments in science events in France, Switzerland, Germany, the Netherlands, and UK.
The main impact of the ITN CREEP has been to:
- contribute to the formation of a new generation of creative, entrepreneurial and innovative young researchers;
- enhance the intersectoral dimension of the doctoral/early stage training in Earth Sciences in Europe;
- advance our understanding of how the complex rheology of Earth and industrial materials controls their mechanical behaviour and the associated economic or societal impacts;
- sensitize young researchers to their responsibility in making scientific research and its outcomes understood by the society;
- promote scientific careers among young Europeans.

These objectives have been successfully fulfilled. Our training/dissemination impact has been enhanced by effective exchanges with other EU projects, like EPOS and other ITNs in Earth Sciences.