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Evolving properties of rocks during fracture growth : from numerical to experimental and in-situ experiments

Final Activity Report Summary - EVOROCK (Evolving properties of rocks during fracture growth : from numerical to experimental and in-situ experiments)

After six years of post-doctoral research, I would like to stress the importance of a Marie Curie Reintegration grant to consolidate and develop a scientific career in Europe. Thanks to this fellowship, I was not only able to continue my research into fracture mechanics of rock, I was also able to initiate some research into environmental and deep Earth geophysics. These new activities and the autonomy in financial matters boosted my accomplishments and improve my position and responsibility within the French research community. New opportunities in finding position arise quite naturally after few months. I am now a teaching assistant in a group of geomorphology working on erosion, deposition and transport mechanisms from the length scales of laboratory experiments to landscape dynamics.

Any summary of work performed has to answer this simple question: how it is possible to work three years on rock mechanics and to get a position in geomorphology?

The answer is in the methodology that was developed during my post-doctoral research, the so-called cellular automata approach. Based on a discrete structure and a finite number of states at an elementary scale, cellular automata are systems that evolve on a network according to local rules of interaction. These rules determine how each element responds to information transmitted from other elements along the network connections. Most of the time, these connections are simplified to include only nearest neighbours interactions. Cellular automata modelling of physical systems are useful tools in social sciences, physical geography, geophysics and biology because their output match very well what we observe in nature without being dependent on a complete description of small scale processes. Thus, the origin of macroscopic phenomena may be analysed from a limited set of parameters via patterns of interaction between different elements of the system over time. Taking advantage of my experience in these modelling techniques, I have implemented models on different types of geophysical environments from aeolian dunes to river beds. These models have found increasing application across Earth and Environmental sciences, a domain in science where the role of heterogeneities is known to be important.

It is only through a deeper knowledge of apparently unrelated phenomena that truly powerful methods can be developed for complex system. Therefore the project has voluntarily explored various geophysical interfaces from deep Earth to surface processes. Major results concern:
1. earthquake sequences (three publications, one submission, one in preparation);
2. population of fractures (two publications, two submissions);
3. population of dunes and landscape dynamics (one publication, one in preparation);
4. reversal sequences of the dipolar magnetic field of the Earth (one publication, one submission).

These results and the development of new partnerships have opened new perspectives in analysing complex geophysical systems. Let us illustrate these perspectives with an example in physical geography. In this domain, the modelling of vulnerable environments has to take into account the evolution of topography over long time (i.e. tectonic, erosion, deposition and transport processes), but also climate changes and modifications in human activities that occurs over much smaller time scales. Then, these environments can be considered as networks in which many physical processes are interacting with one another. In this framework, the cellular automata approach is an efficient calculation strategy for quantitative assessment of feedback mechanisms and it can provide an outstanding background for beginning to address practical management of contemporary ecosystems.