Surface wave interferometry
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Date
2009Author
Halliday, David Fraser
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Abstract
This thesis concerns the application of seismic interferometry to surface waves.
Seismic interferometry is the process by which the wavefield between two recording
locations is estimated, resulting in new recordings at one location as if a source had
been placed at the other. Thus, in surface-wave interferometry, surface waves
propagating between two receiver locations are estimated as if one receiver had
recorded the response due to a source of surface-wave energy at the other receiver. In
global and engineering seismology new surface-wave responses can allow for
imaging of the subsurface, and in exploration seismology it has been proposed that
these new surface-wave responses can allow for the prediction and removal of socalled
ground-roll (surface waves that are treated as noise). This thesis presents a
detailed analysis of surface-wave interferometry: using a combination of modelling
studies, real-data studies, and theoretical analyses the processes involved in the
application of interferometry to complex (both multi-mode and scattered) surface
waves are revealed. These analyses identify why surface waves are often dominant in
the application of interferometry, where errors may be introduced in the application
of surface-wave interferometry, and how interferometry may be processed in such a
way as to minimise those (and other) errors. This allows for the proposal of new
data-processing strategies in the application of seismic interferometry to surface
waves, potentially resulting in improved surface-wave estimates. Much of the work
in this thesis focuses on the use of seismic interferometry to predict and subtract
surface waves in land-seismic exploration surveys. Using insights from the presented
analyses it is shown that seismic surface waves can be successfully predicted and
removed from land-seismic data using an interferometric approach. However, the
work in this thesis is not only limited to applications in exploration seismology. In
addition to the ground-roll removal method, improved estimates of higher-mode and
scattered surfaces waves may allow for more advanced imaging algorithms to be
used in conjunction with seismic interferometry. Also, as a consequence of the analysis presented a Generalized Optical Theorem for Surface Waves is derived.
This highlights a link between seismic interferometry and the optical theorem and
may allow for further application of optical theorems in seismology.