DEEP EARTHQUAKES SPATIAL DISTRIBUTION: NUMERICAL MODELING OF STRESSES WITHIN THE SUBDUCTING LITHOSPHERE

The spatial distribution of deep earthquakes remains elusive. Several mechanical models that have been developed to identify the source distribution fall largely into two categories: (1) models related to thermal and/or compositional anomalies and (2) volume reductions from phase transformations, none of them able to satisfactorily explain the spatial distribution of deep earthquakes (L. Liu and S. Zhang, 2015). Models involving a metastable olivine wedge suggest a continuous and flat spectrum of stress distribution along the slab interior. We model the deformation and stress of the subducting lithosphere using a Particle in Cell method in combination with a conservative finite difference scheme. The software is written in Python and NumPy. We have tested this code for the known results of a Rayleigh–Taylor instability of solid-fluid interaction, and for a general subduction benchmark (Schmeling et al., 2008). We show a large set of numerical models in which we investigate the role of volatiles in the transition zone, by varying the viscosity of the Wadsleyite layer in the upper mantle and the presence of a high viscosity zone below the upper-lower mantle transition zone, as recently proposed by Rudolph et al (2015). Finally we compare the rate of inner energy dissipation and the stored elastic energy in the subducting lithosphere with deep earthquake spatial distribution and discuss which constrains geodynamic models offer to deep earthquake location.Bibliography:

H. Schmeling, A. Y. Babeyko, A. Enns, C. Faccenna, F. Funiciello, T. Gerya, G. J. Golabeka, S. Grigull, B. J. P. Kaus, G. Morra, S. M. Schmalholz, and J. van Hunen, “A benchmark comparison of spontaneous subduction models - towards a free surface”, Physics of the Earth and Planetary Interiors 171 (2008) 198–223.

L. Liu and S.Zhang, “Differential contraction of subducted lithosphere layers generates deep earthquakes”, Earth and Planetary Science Letters 421 (2015) 98–106

M. L. Rudolph, V. Lekić, C. Lithgow-Bertelloni, “Viscosity jump in Earth’s mid-mantle”, Science 350, 1349 (2015); DOI: 10.1126/science.aad1929