Analysis of the mantle heterogeneous velocity structure effect on converted teleseismic waves used to image the transition zone.

Abstract

In this project, we focus on analyzing how the effect of the mantle heterogeneous velocity structure affects the travel time of P waves converted to S waves at the discontinuities of 410 km and 600 km, which mark the so-called mantle transition zone (MTZ). The MTZ is characterized by pressure-induced phase changes in the olivine, the most abundant mineral in the mantle, at its top and bottom and plays a crucial role in the mantle's style convection since it can impede or allow the mass transfer through the MTZ owing to the exothermic/endothermic nature of the phase transitions. Thus, understanding the transition zone structure can provide important information about the prevailing convection style in the Earth's mantle, a problem still open in geodynamics. P waves and their conversions to S waves at discontinuities of 410 km and 660 km, P410s, and P660s, are widely used to determine variations in the MTZ thickness, mainly in regional studies. Here, we will use spectral element seismograms for the PREM model, 3 global seismic tomography models, and 2 regional ones for 48 events distributed in a spiral form from the coordinates -100Ú E and 40 N and recorded by 462 virtual seismic stations in the United States. From stacked synthetic seismograms, we will model travel times with ray theory for the PREM and 3D velocity models to map P410s-P and P660s-P travel time variations and analyze how theoretical simplifications affect the estimation of the MTZ. Additionally, to verify the resolvability of the lateral variations of the mantle discontinuities topography from the receiver function method, we will distort the SPECFEM3D_GLOBE spectral elements mesh to analyze how harmonic variations in the topography, of different wavelengths, may be recovered.