36 Component Seismic Data: Investigating Translational and Rotational Components in Exploration Seismology

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Author
Date
2016-08Type
- Master Thesis
ETH Bibliography
yes
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Abstract
In conventional multicomponent seismic exploration, the wavefield is recorded by measuring translational motions in three directions using three-component sensors. A novel approach in land seismic acquisition is to additionally record the rotational components of the wavefield around the various Cartesian axes and to combine them with translational measurements. Additional rotational
measurements provide the opportunity to locally extract valuable information on the propagating
wavefield, that either cannot be obtained from conventional translational measurements alone or
are challenging to extract. For example, rotational data facilitate wavefield separation, shear-wave
(S-wave) imaging, and ground roll suppression because of the direct link between rotation and the
S-wave component, but also enable local instantaneous phase velocity estimation.
At the Earth’s free surface, rotational motions can be expressed in terms of spatial seismic
wavefield gradients. Wavefield gradients can be estimated by differencing the outputs of closely
spaced three-component translational sensors. The same approach can be adapted to source arrays:
differencing of recordings from closely spaced translational (directed) sources can be used to simulate
rotational sources that primarily emit S-waves. The combination of three components of translation
and three components of rotation on both the source and the receiver side leads to a total of 36 measurable seismic components. In this thesis, I first verify that array-derived rotational rates,
estimated using spatial seismic wavefield gradients, correspond to direct rotation measurements from
rotational sensors. Then, I investigate the value of 36-component seismic data using synthetic as
well as real field data. I show that rotational components around the vertical axis mainly contain
horizontally polarized S-waves. I found that rotational components around the crossline (transverse
horizontal) axis mainly contain ground-roll and vertically polarized S-waves and that these data can
be combined with translational data to suppress ground roll. I show that the amplitudes of rotational
components are dependent on the angle of incidence of the wavefield and that source-sided rotational
components are reciprocal to receiver-sided rotational components.
To accelerate multicomponent acquisition, I furthermore present a new multicomponent seismic
vector-source, which uses the Galperin configuration to obtain orthogonal vector sources of equal
impact patterns and constant source-coupling. This source allows a fast multicomponent dataacquisition in engineering and environmental exploration seismology. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000273384Publication status
publishedPublisher
ETH ZurichSubject
Rotational seismology; SEISMIC EXPLORATION + SEISMIC SOUNDING (APPLIED GEOLOGY AND GEOPHYSICS); SHEAR WAVES (GEOPHYSICS); seismic sources; multicomponent seismologyOrganisational unit
01656 - MSc Applied Geophysics / MSc Applied Geophysics
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ETH Bibliography
yes
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