Large scale interactions on a subduction zone : insight from numerical models

6 mois

Subduction zones host the world largest earthquakes, and understanding how these earthquakes initiate and interact is an important challenge in earth science. Puzzling observations show that large earthquake can cluster in space and time. Large scale interactions along the strike of the subduction zone have been observed, for example the apparent changes in the plate interface locking after a large earthquake. Also, interaction between deep (>100km) and shallow (>40 km) seismicity have been suggested. In both cases, these observations are unexplained by classical static stress interactions as they occur at distances of hundreds to thousand of kilometers, and also fail to be explained by post-seismic relaxation mechanism. One potential candidate to ex-plain these phenomenon is the role played by the rigid subducting slab, and potential low viscosi-ty channel in the vicinity of the slab, that could help to transfer stresses at large distances over a subduction zone.

During this Master project, we propose to study via numerical simulation how a subduction zone adjusts to the perturbation created by a large earthquake. The simulations will provide theoretical surface deformation fields, which can be compared with real observations such as GNSS data. They will also provide the temporal evolution of normal and shear stresses along the subduction interface away from the initial earthquake location which can help to understand the potential in-teractions with subsequent events. Furthermore, they will allow to quantify the excess corner flow and slab velocity created by a large subduction earthquake.

Different mechanical scenarios will be considered, in each case imposing the displacement pro-duced by a large earthquake, and varying the rigidity of the slab and the viscosity of the asthe-nosphere. For each scenario, we will assess the distance of interactions and the time scales in-volved. The results will be qualitatively compared to published observations of triggered slip far away from large earthquakes (e.g., Tokashi-Oki 2003 - Tohoku 2011, Maule 2010 –Illapel 2015) The numerical simulations will be performed using the finite element code Pylith. We will first start with a 2D configuration, in which we will assess the potential link between deep and shallow seismicity. In a second step, a 3D model will be constructed in order to assess the along-strike interactions.

A solid background in Mathematics, Geophysics and Computation is required for this master project. The student will work within the “Seismic cycle and transient deformation” team in ISTerre laboratory, Grenoble. This master project aims at being continued and widened dur-ing a PhD for which a scholarship is already guaranteed through the project DEEP-trigger funded by the European Research Council. The student will interact with the group of stu-dents and researchers involved in the project, and with collaborators in France and abroad.

contacts anne.socquet -at- univ-grenoble-alpes.fr
mathilde.radiguet -at- univ-grenoble-alpes.fr