##### A multi-azimuth seismic refraction study for a horizontal transverse isotropic medium: physical modelling results

Authors:
C.-W. Tseng, Y.-F. Chang, J.-W. Liu and C.-M. Lin

Journal name: Geophysical Prospecting

Issue: Vol 66, No 1, January 2018 pp. 13 - 25

DOI: 10.1111/1365-2478.12526

Organisations:
Wiley

Language: English

Info: Article, PDF ( 9.56Mb )

Summary:

To investigate the characteristics of the anisotropic stratum, a multi-azimuth seismic
refraction technique is proposed in this study since the travel time anomaly of the refraction
wave induced by this anisotropic stratum will be large for a far offset receiver.
To simplify the problem, a two-layer (isotropy–horizontal transverse isotropy) model
is considered. A new travel time equation of the refracted P-wave propagation in this
two-layer model is derived, which is the function of the phase and group velocities of
the horizontal transverse isotropic stratum. In addition, the measured refraction wave
velocity in the physical model experiment is the group velocity. The isotropic intercept
time equation of a refraction wave can be directly used to estimate the thickness
of the top (isotropic) layer of the two-layer model because the contrast between the
phase and group velocities of the horizontal transverse isotropic medium is seldom
greater than 10% in the Earth. If the contrast between the phase and group velocities
of an anisotropic medium is small, the approximated travel time equation of a refraction
wave is obtained. This equation is only dependent on the group velocity of the
horizontal transverse isotropic stratum. The elastic constants A11, A13, and A33 and
the Thomsen anisotropic parameter ε of the horizontal transverse isotropic stratum
can be estimated using this multi-azimuth seismic refraction technique. Furthermore,
under a condition of weak anisotropy, the Thomsen anisotropic parameter δ of the
horizontal transverse isotropic stratum can be estimated by this technique as well.

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