Global Seismic Full-Waveform Inversion

Abstract

This dissertation details the construction of a tomographic model of the Earth's crust

and mantle based on seismic full-waveform inversion (FWI). The new model involves

a database of 1,480 earthquakes in the magnitude range 5.5 < Mw < 7.2 recorded

by more than 11,000 global seismographic stations. The approach utilizes 3D simulations

of global seismic wave propagation with a shortest period of 17 s accelerated by

Graphics Processing Units (GPUs), requiring access to the world's largest and fastest

supercomputers. These simulations accommodate eects due to 3D anelastic crust

& mantle structure, topography & bathymetry, the ocean load, ellipticity, rotation,

and self-gravitation. An adjoint-state method is used to calculate Frechet derivatives

in 3D anelastic Earth models facilitated by a parsimonious storage algorithm.

The construction of the model, named GLAD-M25, posed numerous challenges. The

Adaptable Seismic Data format (ASDF) was designed to meet the requirements and

standards of modern data containers, accommodating fast parallel I/O and full data

provenance. To manage the complex and fragile iterative global tomographic inversion,

workflow management tools were introduced to automate and harden the process.

To balance the uneven distribution of earthquakes and stations, a geographical

weighting scheme was introduced, thereby speeding up convergence in the iterative

quasi-Newton inversion algorithm. The new model was evaluated by assessing mist

reductions and traveltime & amplitude anomaly histograms in four period bands on

three seismographic components. Similar assessments were made for a held-out data

set consisting of 360 earthquakes, with results comparable to the actual inversion. All

of these evaluations show that model GLAD-M25 produces signicant improvements

in t. GLAD-M25 is compared with numerous other global and regional models,

and a wide variety of plumes and subduction zones are highlighted. These comparisons

demonstrate that GLAD-M25 has unprecedented resolution compared to other

global-scale models, approaching that of regional- and continental-scale models of

the upper mantle. These improvements in resolution provide new insights into the

dynamics and evolution of the Earth's interior.