Analysis of converted refractions for shear statics and near-surface characterisation
Alan Meulenbroek 1 Steve Hearn 1 21 Velseis Pty Ltd and School of Earth Sciences, University of Queensland, PO Box 118, Sumner Park, QLD 4074, Australia.
2 Corresponding author. Email: steveh@velseis.com
Exploration Geophysics 42(2) 147-154 https://doi.org/10.1071/EG10031
Submitted: 27 October 2010 Accepted: 26 May 2011 Published: 28 June 2011
Abstract
Converted-wave refraction statics is an algorithm that incorporates both P-wave and S-wave refraction events to correct S-wave static errors in multicomponent seismic data. Conventional (PPP) and converted (PPS) refractions are picked on vertical and inline-horizontal shot records respectively. These picks are then analysed using the reciprocal method to create a near-surface model from which S-wave receiver statics are derived.
The derived PPS refraction statics have a similar short-wavelength character to S-wave statics obtained via statistical analysis of converted-wave reflections. Based on standard P-wave practice, we believe that an optimal production approach will include converted-refraction analysis, followed by converted-wave residual statics.
Although the thrust of this work has been towards derivation of S-wave statics, an interesting auxiliary output is also available. Based on theoretical modelling, the observed S-to-P time-depth ratios can be tuned to provide P-to-S velocity ratios (and hence dynamic Poisson’s ratios) for the near-surface. This has interesting implications for lithological and rock strength analysis in mining, geotechnical and environmental investigations.
Key words: converted-wave, multi-component seismic, near-surface, refraction, shear-wave statics.
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