Global study of the mantle transition zone structure from SS wave propagation.

Abstract

Understanding the mantle transition zone structure can provide important constraints on the convection style that prevails in the mantle, a fundamental open problem in geodynamics. The transition zone is characterized by phase changes in olivine, the most abundant mineral in the mantle, and plays a key role in determining the mantle convection style, either layered convection or whole-mantle convection. In this proposal of research internships abroad, we focus on determining the topography of the 410 and 660 km discontinuities using traveltimes of SS precursors analysis. We will make a critical evaluation of currents methods used to derive such topographies, trying to understand how theoretical simplifications on the ray theory could affect the estimative of the transition zone thickness. Using the finite frequency theory and global seismic tomography models, we intent to derive more accurate maps of the undulations at the 410 and 660 km discontinuities. These maps will be used as a priori information in the inversion of geoid anomalies to determine a density distribution model within the transition zone. A joint interpretation of the thickness variation of the transition zone, which is frequently used as a "thermometer" of the mantle, the signal of the density contrast and the laboratorial experiments provided by mineral physics will give us more reliable results about the actual mantle thermal state around our planet.