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Kurama Okubo receives the 2020 CNFGG Geophysics Thesis Prize

Kurama Okubo receives the 2020 CNFGG Geophysics Thesis Prize

Publication date: 18/11/2020

Awards and Distinctions, Institute Life, Press, Research

Since 1989, the CNFGG has awarded an annual prize for a thesis in geophysics to one or more young researchers who have submitted outstanding theses in the field of geophysics, either for their fundamental or observational aspects or for their potential applications in society.

Kuruma Okubo, a doctor from the IPGP, is one of the winners of the Geophysics 2020 prize. Kurama Okubo defended his thesis, carried out jointly at IPGP and ENS-PSL under the supervision of Harsha Bhat and Yann Klinger, in November 2018. After a spell at Harvard, he has been a researcher at the National Research Institute for Earth Science and Disaster Resilience (NIED) in Japan since October 2020.

His thesis, which won the CNFGG prize, focused on the dynamics of earthquakes on multi-scale fault zones and fractures:

Natural fault zones are structurally complex at different scales. They are composed of a network of major faults, where the main slip occurs, itself surrounded by a meso- and microscopic network of fractures. This geometric complexity has an impact on rupture dynamics, seismic wave propagation and the energy balance during earthquakes. In this study, in order to be able to model seismic ruptures along faults with realistic geometry, associated with the creation of secondary fractures, we propose an approach that combines the modelling of continuous and discontinuous media, using the combined finite and discrete element method (FDEM). We first present the results of dynamic fracture modelling with secondary fracture generation. These simulations illustrate the damage mechanisms, a decrease in fracture rate, and high-frequency near-field radiation. The energy budget is also modified due to radiation and the dissipation of fracture energy associated with damage. We then carried out numerical experiments to reproduce dynamic rupture during the Kaikōura earthquake (magnitude 7.8), which occurred in 2016, on the South Island fault system of New Zealand. We were able to demonstrate that, by comparing field observations with the nature of the damage and the displacement profiles generated by our models, it is possible to discriminate between different potential coseismic rupture scenarios. In conclusion, the work carried out during this thesis proposes a new generation of models which, thanks to the combined approach of continuous and discrete media, enables the activation and generation of secondary fracture systems in connection with earthquakes on major faults. They demonstrate the significant effects that damage generated during earthquakes can have.

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