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Title: Structure and heterogeneity of the Earth's mantle from broadband earthquake seismology
Author: Sharrock, David Stuart
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Attenuation of seismic energy is often seen as an unavoidable 'problem' in earthquake seismology. Observation of earthquakes at teleseismic distances is severely limited by the signal-to-noise ratio of the recording seismograph. However, the underlying mechanisms behind seismic attenuation are very different to those underlying other parameters and seismic attenuation can yield information on the structure of the Earth different to that obtained from, for example, seismic wave speed studies. In this study, 59 globally-distributed earthquakes and explosions, recorded at the four UK-type arrays in Eskdalemuir (Scotland), Gauribidanur (India), Warramunga (Australia), and Yellowknife (Canada), have been used to investigate the seismic attenuation along the P-wave propagation path in the frequency range 1-8 Hz. Two advantages of using array data, without which this study would have been unfeasible, are that the array seismographs record data over a wider frequency band (1-8 Hz) than many short-period instruments, and the method of 'beam-forming' seismic array data enhances the signal-to-noise ratio. The scatter of the data suggest that the upper mantle is inherently heterogeneous on scale-lengths of as little as 1-2 km. The difference between low-frequency and high-frequency models is attributed to scattering near-surface, and to strain rate effects in the lower mantle, however, the attenuation in the upper mantle at high frequencies shows an anomalous jump which is difficult to explain but may be due to a change in mantle behaviour for larger strain rates (increased frequency in cyclic loading).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available