UBC Theses and Dissertations
Seismic energy propagation in highly scattering environments and constraints on lunar interior structure from the scattered signals of the Apollo passive seismic experiment Blanchette-Guertin, Jean-François
Meteoroid impacts over hundreds of millions to billions of years can produce a highly fractured and heterogeneous megaregolith layer on planetary bodies such as the Moon that lack effective surface recycling mechanisms. The energy from seismic events occurring on these bodies undergoes scattering in the fractured layer(s) and this process generates extensive coda wave trains that follow major seismic wave arrivals. These long coda trains can obscure the secondary crustal, mantle or core phases that are often crucial in assessing the interior structure of these planetary bodies when using more traditional seismological analyses. However, the decay properties of these codas are affected by the interior velocity, intrinsic attenuation and scattering structure of the planet or moon. As such, these decay properties can contain valuable information regarding these aspects of interior structure. This thesis provides the first systematic analysis of scattering in the Apollo Passive Seismic Experiment dataset, demonstrating that scattering in the Moon occurs over a wide range of frequencies, and dominantly in the near-surface megaregolith that comprises many more small scale heterogeneities than large ones. I also present a new numerical modeling technique (referred to as PHONON1D) that models seismic energy propagation and integrates high levels of scattering. Using this method, I investigate the effects of various velocity, scattering and intrinsic attenuation structures on the scattered coda. Results show that the main controls on the coda generation and decay times are the seismic velocity profile, attenuation levels, and the number density of scatterers. Thus these properties can be assessed by comparing predicted synthetic seismic coda with those observed in the Apollo Passive Seismic Experiment data. Finally, I use the PHONON1D method to show that locations within young and large impact basins, away from the edges, have the potential to minimize the scattering observed in the recorded seismic signals. These locations would be ideal for the emplacement of future seismic surveys on the lunar surface.
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Attribution-NonCommercial-NoDerivs 2.5 Canada