Global seismic tomography: Present status and future perspectives

Global seismic tomography of the Earth’s mantle has traditionally focused on the inversion of travel times from a small number of seismic phases, well isolated in time domain seismograms. The resulting uneven sampling of the Earth, dictated by the available distribution of earthquake sources and receivers, greatly limits the resolution of 3-D structure that can be attained. With recent progress in the simulation of wave propagation in realistic 3-D Earth models combined with significant increases in computational power, seismologists are well positioned to start fully exploiting the wealth of information contained in the rapidly expanding database of high quality broadband seismic waveforms, accumulated globally and regionally over the last twenty five years. New opportunities presented by 3-D forward and inverse modeling of long period waveforms will be presented with illustrations from recent work on deep and shallow elastic and anelastic mantle structure, addressing, among others, such questions as: what is the fate of subducted slabs or the nature of the lower mantle ‘‘superplumes’’?