Seismic rays, interface refraction and travel time
In a high-frequency ray model, travel time along a pathγ is t=∫_γ ds/v.
Key knowledge
In a high-frequency ray model, travel time along a pathγ is t=∫_γ ds/v. Across a stationary planar interface, matching phase along the interface gives sinθ₁/v₁=sinθ₂/v₂ for propagating branches, with angles from the normal. For v₂>v₁ the transmitted grazing angle occurs at sinθ_c=v₁/v₂. Reflection and converted elastic branches require their own speeds and boundary conditions.
Values and equations
t=∫_γ ds/v; sinθ₁/v₁=sinθ₂/v₂; sinθ_c=v₁/v₂ (v₂>v₁)
- t
- ray travel time s
- s
- distance along a ray m
- v,v₁,v₂
- local branch propagation speeds m s⁻¹
- θ₁,θ₂,θ_c
- angles from the interface normal rad
Conditions and scope
- Wavelength is small compared with the smooth variation scale away from interfaces; local isotropic phase speeds and a time-independent medium. The actual path must satisfy the ray/interface conditions.
- Beyond a critical angle, absence of a propagating transmitted branch does not imply absence of evanescent fields or mode conversion. Amplitudes, diffraction, caustics, attenuation and anisotropic group directions require wave treatment; mechanical particle-momentum conservation is not the derivation of Snell phase matching.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual printed17–19 interface reflection/refraction/conversion and critical-angle bodies. The path integral is the disclosed infinitesimal distance/speed definition and tangential phase continuity supplies the corrected derivation. Excluded no-evanescent/all-energy-reflected wording, mechanical momentum argument and the later blanket depth-speed claim.
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Entry details
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