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Home/Biophysics, Fluids & Geoscience/Layered Medium: P/S Fronts & Hodograph

Layered Medium: P/S Fronts & Hodograph

P and S in a two-layer straight-ray toy: reflected legs and optional head branches when the lower layer is faster; hodograph plus minimum-time first arrivals (no conversions or amplitudes).

Layer model

4.5 km/s
6.8 km/s
2.55 km/s
3.85 km/s
12 km
120 km

Schematic P- and S-wave travel times (same two-layer ray geometry): reflected leg through the top layer and, when the basement is faster, a head wave along the interface after the critical distance. The bottom graph is the minimum time among the four body-wave branches at each offset — kinematic cartoon only (no amplitudes, no converted phases).

Measured values

P head possibleyes
S head possibleyes

Straight-ray two-layer model; default v_S ≈ 0.57 v_P is typical order-of-magnitude for crustal rocks, but you should tune both pairs independently.

Live graphs

About this model

P- and S-waves share the same two-layer straight-ray geometry: a reflected leg through the upper layer and, when the basement is faster, a head wave along the interface after the critical distance. The hodograph plots each mode’s branches; the lower panel is the minimum time over the four body-wave branches at each offset (kinematic sketch only).

Who it's for: Introductory geophysics or exploration seismology students.

Key terms

  • Head wave
  • Critical refraction
  • Hodograph
  • Layered medium
  • S-wave

How it works

Layered-earth cartoon: P and S head waves when the lower layer is faster; hodograph (t–x) shows crossover between reflected and head branches and the fastest body-wave arrival.

Frequently asked questions

Are amplitudes, mode conversions, or curved rays included?
No. Only schematic travel times for reflected and head branches of P and S, with an independent (v_S1, v_S2) pair; the envelope is the fastest of those four branches at each offset.