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Beamforming and Polarisation analysis
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.
Funding
Australian Research Council
History
Publication title
Seismic Ambient NoiseEditors
N Nakata, L Gualtieri, and A FichtnerPagination
32-72ISBN
9781108264808Department/School
School of Natural SciencesPublisher
Cambridge University PressPlace of publication
United KingdomExtent
10Repository Status
- Restricted