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Ambient Seismic Noise Interferometry on the Island of Hawai‘i.

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Title:Ambient Seismic Noise Interferometry on the Island of Hawai‘i.
Authors:Ballmer, Silke
Contributors:Geology & Geophysics (department)
Keywords:Ambient seismic noise interferometry
volcanic tremor
volcano monitoring
show 1 moresurface wave tomography
show less
Date Issued:May 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Ambient seismic noise interferometry has been successfully applied in a variety of tectonic
settings to gain information about the subsurface. As a passive seismic technique, it extracts the
coherent part of ambient seismic noise in-between pairs of seismic receivers. Measurements of
subtle temporal changes in seismic velocities, and high-resolution tomographic imaging are then
possible – two applications of particular interest for volcano monitoring. Promising results from
other volcanic settings motivate its application in Hawai‘i, with this work being the first to
explore its potential. The dataset used for this purpose was recorded by the Hawaiian Volcano
Observatory’s permanent seismic network on the Island of Hawai‘i. It spans 2.5 years from
5/2007 to 12/2009 and covers two distinct sources of volcanic tremor. After applying standard
processing for ambient seismic noise interferometry, we find that volcanic tremor strongly affects
the extracted noise information not only close to the tremor source, but unexpectedly, throughout
the island-wide network. Besides demonstrating how this long-range observability of volcanic
tremor can be used to monitor volcanic activity in the absence of a dense seismic array, our
results suggest that care must be taken when applying ambient seismic noise interferometry in
volcanic settings. In a second step, we thus exclude days that show signs of volcanic tremor,
reducing the dataset to ~three months, and perform ambient seismic noise tomography. The
resulting two-dimensional Rayleigh wave group velocity maps for 0.1 – 0.9 Hz compare very
well with images from previous travel time tomography, both, for the main volcanic structures at
low frequencies as well as for smaller features at mid-to-high frequencies – a remarkable
observation for the temporally truncated dataset. These robust results suggest that ambient
seismic noise tomography in Hawai‘i is suitable 1) to provide a three-dimensional S-wave model
for the volcanoes and 2) to be used for repeated time-sensitive tomography, even though volcanic
tremor frequently obscures ambient noise analyses. However, the noise characteristics and the
wavefield in Hawai‘i in general remain to be investigated in more detail in order to measure
unbiased temporal velocity changes.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Geology and Geophysics

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