Elastic and anelastic Full-Waveform Inversion across scales

Type
Thesis

Authors
Espindola Carmona, Armando

Advisors
Mai, Paul Martin

Committee Members
Bozdag, Ebru
Hoteit, Hussein
Alkhalifah, Tariq

Program
Earth Science and Engineering

KAUST Department
Physical Science and Engineering (PSE) Division

Date
2023-09

Abstract
Improving the resolution of seismic models is critical for enhancing our understanding of the Earth's subsurface structure and dynamics. Full-Waveform Inversion (FWI) has emerged as the most promising approach for connecting high-resolution body wave tomography with lower-resolution surface wave tomography at local, regional, and global scales. The advantage of theoretically assimilating every recorded wiggle from seismic stations to infer the Earth's internal structure further emphasizes the need to investigate the robustness, resolution, and uncertainty of the resulting seismic models. Furthermore, in a multi-parameter FWI framework, several challenges arise from the coupling effects between parameters and their variable influences on the phase and amplitude of the data. In this thesis, I present studies using synthetic and real data, where I explore different strategies to tackle these issues at three different scales.

At the local scale, I present a 3-D elastic model of central and southern Mexico. For this, I develop a 3-D finite difference code and FWI workflow. The tomographic model reveals several seismic wave speed anomalies consistent with previous studies, along with new wave speed anomalies that are correlated with tectonic tremors and silent earthquake regions.

At the global scale, I perform a series of realistic synthetic experiments to analyze the resolution, the trade-offs between elastic and anelastic parameters, and suitable strategies to retrieve seismic attenuation. I suggest a sequential approach to recover attenuation that first updates the elastic structure and then simultaneously updates the anelastic and elastic parameters. This with an envelope misfit function may ensure a stable and accurate reconstruction in a multi-parameter anelastic FWI framework.

Finally, at a regional scale, I apply multi-parameter FWI for the Arabian Peninsula. Here, I fit amplitude and traveltime information jointly to constrain the anelastic and elastic structure in the upper-mantle. The new tomographic model reveals low wave speed anomalies that are consistent with previous studies and associated with mantle material from the Afar plume. Furthermore, I observe high shear attenuation anomalies beneath the southern and central parts of the Arabian Shield. I suggest that these regions are related to either the hot asthenosphere from the Afar plume or partial melting triggered by lithospheric thinning along the Red Sea rift.

DOI
10.25781/KAUST-WCXV8

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