Studies of seismic deconvolution and low-frequency earthquakes
department or school: Science, Faculty of
department or school: Earth, Ocean and Atmospheric Sciences, Department of
data provider: DSpace
degree campus: UBCV
creator: Royer, Alexandra Amélie
issued: 2014-08-11T15:01:21Z
issued: 2014
related degree: Doctor of Philosophy - PhD
degree grantor: University of British Columbia
description: Deconvolution of seismic data is an important component of signal processing that aims to remove the seismic source from seismograms, thereby isolating the Green’s function. By considering seismograms of multiple earthquakes from similar locations recorded at a given station and that therefore share the same Green’s function, we investigate a system of equations where the unknowns are the sources and source durations. Our solution is derived using direct linear inversion to recover the sources and Newton’s method to recover source durations. For the short seismogram durations considered, we are able to recover source time functions for noise levels at 1% of the direct P -wave amplitude. However, the nonlinearity of the problem renders the system expensive to solve and sensitive to noise; therefore consideration is limited to short seismograms with high signal-to-noise ratio (SNR). When SNR levels are low, but a large multiplicity of seismograms representing a common source-receiver path are available, we can apply a different deconvolution approach to recover the Green’s function. In an application to tectonic tremor in northern Cascadia, we implement an iterative blind deconvolution method that involves correlation, threshold detection and stacking of 1000’s of low frequency earthquakes (LFEs) that form part of tremor to generate templates that can be considered as empirical Green’s functions. We exploit this identification to compute hypocentres and moment tensors. LFE hypocentres follow the general epicentral distribution of tremor and occur along tightly defined surfaces in depth. The majority of mechanisms are consistent with shallow thrusting in the direction of plate motion. We analyze the influence of ocean tides on the triggering of LFEs and find a spatially variable sensitivity to tidally induced up-dip shear stress (UDSS), suggesting that tidal sensitivity must partially depend on laterally heterogeneous physical properties. The majority of LFEs fail duri…
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/49978
note: Studies of seismic deconvolution andlow-frequency earthquakesbyAlexandra Ame´lie RoyerB. Sc. Universite´ Joseph Fourier, 2007M. Sc. Universite´ Joseph Fourier, 2009A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinThe Faculty of Graduate and Postdoctoral Studies(Geophysics)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)August 2014c© Alexandra Ame´lie Royer, 2014iiAbstractDeconvolution of seismic data is an important component of signal processing thataims to remove the seismic source from seismograms, thereby isolating the Green’sfunction. By considering seismograms of multiple earthquakes from similar locationsrecorded at a given station and that therefore share the same Green’s function, we inves-tigate a system of equations where the unknowns are the sources and source durations.Our solution is derived using direct linear inversion to recover the sources and Newton’smethod to recover source durations. For the short seismogram durations considered,we are able to recover source time functions for noise levels at 1% of the direct P -waveamplitude. However, the nonlinearity of the problem renders the system expensive tosolve and sensitive to noise; therefore consideration is limited to short seismograms withhigh signal-to-noise ratio (SNR). When SNR levels are low, but a large multiplicity ofseismograms representing a common source-receiver path are available, we can apply adifferent deconvolution approach to recover the Green’s function. In an application totectonic tremor in northern Cascadia, we implement an iterative blind deconvolutionmethod that involves correlation, threshold detection and stacking of 1000’s of low fre-quency earthquakes (LFEs) that form part of tremor to generate templates that canbe considered as empirical Green’s functions. We exploit this identification to computehypocentres and moment tensors. LFE hypocentres follow the general epicentral dis-tribution of tremor and occur along tightly defin…
has type: Thesis/Dissertation
date issued: 2014-09
is shown at: 10.14288/1.0165914
language: eng
degree discipline: Geophysics
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: Attribution-NonCommercial-NoDerivs 2.5 Canada
rights URI: http://creativecommons.org/licenses/by-nc-nd/2.5/ca/
scholar level: Graduate
type: Text
identifier URI: http://hdl.handle.net/2429/49978