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Beamforming and Polarisation analysis

Citation

Gal, M and Reading, AM, Beamforming and Polarisation analysis, Seismic Ambient Noise, Cambridge University Press, N Nakata, L Gualtieri, and A Fichtner (ed), United Kingdom, pp. 32-72. ISBN 9781108264808 (2019) [Research Book Chapter]


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DOI: doi:10.1017/9781108264808.004

Abstract

Beamforming and polarisation analysis are two approaches to seismic data analysis which aim to determine the wave type and source location of the incoming signal. Beamforming is viable where seismic signals are recorded by an array of 1- or 3-component stations, while polarisation analysis techniques exist for both 3-component arrays and single 3-component stations. The majority of permanent seismic arrays were deployed as part of the International Monitoring System to improve the detection of nuclear explosions. Such arrays are optimised for events occurring one at a time, with an impulsive onset, tightly constrained location, and short duration. In contrast, ambient seismic noise occurs at many locations simultaneously with relatively low amplitude, has no sharp onset and may have moving sources. The range of methods that may be used to estimate the slowness and backazimuth of incoming energy arriving at the array are reviewed and discussed as well as developments of such methods that improve the observation of ambient noise, its location and character.

Single component plane wave beamforming in the form of conventional frequency-wavenumber (f-k) analysis and data adaptive beamforming (MVDR / Capon) is introduced. Almost all array observations of seismic noise, e.g. source localisation of Rayleigh, Lg, P waves and power measurements, can be attributed to these two techniques which have solidified the understanding between theory, numerical modelling and observations. The choice of array design impacts on the resolution for a given frequency range for the intended task. The theory for the underlying beamforming techniques is related to the array design and further strategies are discussed to optimise beamforming for the analysis of microseisms.

Methods for investigating the polarisation of incoming ambient noise signals are presented for seismic arrays and 3-component stations. Multiple ways are reviewed to extend the beamformers described previously for an analysis of the 3-component wavefield, which allows for the observation of shear surface and body waves and improves overall performance. For single station 3-component sensors, a review of the most commonly used polarisation methods in the context of microseism analysis is given.

Item Details

Item Type:Research Book Chapter
Keywords:seismic array, ambient noise, beamforming, polarisation,
Research Division:Earth Sciences
Research Group:Geophysics
Research Field:Seismology and Seismic Exploration
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
UTAS Author:Gal, M (Mr Martin Gal)
UTAS Author:Reading, AM (Professor Anya Reading)
ID Code:136548
Year Published:2019
Funding Support:Australian Research Council (DP150101005)
Deposited By:Mathematics and Physics
Deposited On:2020-01-07
Last Modified:2020-01-21
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