Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Earth and Planetary Sciences

Language

English (en)

Date of Award

Winter 1-1-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Michael E Wysession

Abstract

In this thesis I discuss some existing array techniques and extend them in new ways to study specific seismic phases with immense amounts of seismic data. The results of this new and unique dataset have implications on the state and natural processes occurring in two main regions of the Earth: the bottom of the mantle and the near-surface of the Earth. Chapter 2 analyzes more than one million frequency-dependent measurements of the ray parameter: horizontal slowness) and decay constant of both Pdiff and SHdiff waveforms for more than 100 earthquakes to observe the influence of geographic variations of lowermost mantle seismic velocity structure on these waves. I am able to show that the large, low provinces noted in many whole-mantle tomography models are the most significant lower mantle influence on both seismic phases. Furthermore, I am able to quantify the frequency dependence of these phases and how that dispersion varies with geographic position, which has implications on both the radial and lateral seismic velocity structure. Chapter 3 locates body wave microseism sources using techniques dating back to the 1960s. The most significant difference of this study compared to previous ones is that it focuses on microseisms recorded in Africa and it uses 4 arrays in a rather close geometry instead of a single array or arrays located on different continents. The results show that three factors play a critical role in the generation of body wave microseisms: ocean wave heights, coastlines and bathymetry. Chapter 4 explores the seasonal patterns in Rayleigh wave microseisms in equatorial and southern Africa and the main source locations using a new frequency-domain surface-wave back-projection method. The results illustrate that the main sources of microseisms propagating through equatorial and southern Africa come from near the coast and certainly on the continental shelves. In one case, my results directly contradict a previous study on the source location of microseisms in Tanzania. In another case, I am able to localize a persistent source of Rayleigh wave microseisms in South Africa from across an ocean basin.

Comments

Permanent URL: http://dx.doi.org/10.7936/K7G73BR4

Download

Share

COinS