Reflection moveout approximation for a P-SV wave in a moderately anisotropic homogeneous vertical transverse isotropic layer

0501098 - GFÚ 2020 RIV US eng J - Journal Article
Farra, V. - Pšenčík, Ivan
Reflection moveout approximation for a P-SV wave in a moderately anisotropic homogeneous vertical transverse isotropic layer.
Geophysics. Roč. 84, č. 2 (2019), C75-C83. ISSN 0016-8033. E-ISSN 1942-2156
R&D Projects: GA ČR(CZ) GA16-05237S
Institutional support: RVO:67985530
Keywords : reflection moveout * transverse anisotropy * converted wave
OECD category: Volcanology
Impact factor: 2.609, year: 2019
Method of publishing: Open access
https://library.seg.org/doi/10.1190/geo2018-0474.1

A description of the subsurface is incomplete without the use of S-waves. Use of converted waves is one way to involve S-waves. We have developed and tested an approximate formula for the reflection moveout of a wave converted at a horizontal reflector underlying a homogeneous transversely isotropic layer with the vertical axis of symmetry. For its derivation, we use the weak-anisotropy approximation, i.e. we expand the square of the reflection traveltime in terms of weak-anisotropy (WA) parameters. Traveltimes are calculated along reference rays of converted reflected waves in a reference isotropic medium. This requires the determination of the point of reflection (the conversion point) of the reference ray, at which the conversion occurs. This can be done either by a numerical solution of a quartic equation or by using a simple approximate solution. Presented tests indicate that the accuracy of the proposed moveout formula is comparable with the accuracy of formulas derived in a weak-anisotropy approximation for pure-mode reflected waves. Specifically, the tests indicate that the maximum relative traveltime errors are well below 1% fix models with P- and SV-wave anisotropy of approximately 10% and less than 2% for models with P- and SV-wave anisotropy of 25% and 12%, respectively. For isotropic media. the use of the conversion point obtained by numerical solution of the quartic equation yields exact results. The approximate moveout formula is used for the derivation of approximate expressions for the two-way zero-offset traveltime, the normal moveout velocity and the quartic term of the Taylor series expansion of the squared traveltime.
Permanent Link: http://hdl.handle.net/11104/0293102