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Annual Report 2000 - WIT

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28<br />

is formulated in such a way that the influence of the curved surface can be clearly<br />

recognized.<br />

THEORY<br />

According to (Schleicher et al., 1993), the hyperbolic traveltime approximation for a<br />

ray from ¢£ to ¢¤£ and from ¢¤£ to ¤:£ both on a curved surface, in the vicinity of a<br />

normal (zero-offset) ray from ¢Œ¤ to ¢ and from ¢ to ¢Œ¤ (Figure A-1) is given by<br />

(1)<br />

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with<br />

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This formula is valid for a 2D laterally inhomogeneus medium. is the velocity at the<br />

ZO location , is zero-offset (two-way) traveltime. and are the coordinates<br />

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of ©½ the source Wº and receiver measured along the tangent to the curved surface ¢£ at<br />

¤:£<br />

. ¢Œ¤<br />

The components °(|¬ |¾V|¿ of the so-called ÁÀÂ surface-to-surface propagator<br />

matrix for the two-way normal ray (see Appendix) are given by<br />

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,f.<br />

where · ¸ is the angle of incidence of the normal ray (emerging on the curved<br />

measurement surface ¢Œ¤ at ) with the normal of the tangent to the curved surface at<br />

. Let us define à · as the surface curvature at the point ¢Œ¤ . £3¦6¨ and à £ are<br />

¢Œ¤<br />

the curvatures of the NIP-wave and the N-wave observed ¢Œ¤ at , respectively (Hubral,<br />

1983; Jäger et al., 2001).<br />

· ¸ 4

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