Investigating elastic properties with full-waveform inversion at the hikurangi margin
File(s)
Author(s)
Frahm, Laura
Type
Thesis
Abstract
Full-waveform inversion (FWI) is an inversion technique that generates high-resolution physical property models of the subsurface. The NZ3D dataset was acquired to perform FWI and generate P-wave velocity models of the Hikurangi margin. In this project, I develop a reliable workflow to apply FWI on this dataset. I perform a 2D FWI that images the accretionary wedge as well as the d´ecollement and a 3D inversion which focusses on a near-surface area within the accretionary wedge. This area is characterized by a thrust ridge with a relatively strong bottom-simulating reflector (BSR). In order to investigate this BSR, I apply a newly developed method that allows the use of acoustic FWI to analyse the amplitude-versus-offset (AVO) effect in the seismic data and, thereby, resolve the elastic parameters and investigate the fluid distribution along the BSR. While the applicability of this method has been proven for synthetic data, this study is the first to apply it to field data. Additionally, I perform rock-physics modelling for the study area which allows me to relate the P-wave velocities in the FWI model to rock properties providing gas hydrate and free gas saturation estimates for the BSR and a quality control for the application of the FWI AVO method. I jointly interpret the results from the FWI, the FWI AVO analysis and the rock-physics modelling to identify the cause of the investigated BSR. The BSR is characterised by a higher gas saturation within the basin which decreases towards the ridge and vice-versa for the gas hydrate saturation. The gas hydrate was probably generated during the process of hydrate recycling and sourced by free gas flow from below the BSR into the gas hydrate stability zone along permeable structures.
Version
Open Access
Date Issued
2024-07-01
Date Awarded
01/02/2025
License URL
Advisor
Bell, Rebecca
Morgan, Joanna
Davy, Richard
Sponsor
The Leverhulme Trust
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)