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The lack of sharp velocity contrasts mean there are no clearly
observable reflections in the impulse response. The visible events
are diving waves (refractions) of increasing order.
The first arrival is the the direct wave that would be characterized
as the `P' arrival in terrestrial geophysics. The second arrival is
equivalent to a `PP' event (or first order multiple) having bounced
once on the solar surface.
About six distinct arrivals are visible in
Figure 3, corresponding to multiples up to
fifth-order.
Since there are no distinct velocity interfaces, only a smooth
velocity gradient, the head waves continually curve upward. The
contrast between this behavior and head waves on terrestrial
exploration seismograms is illustrated in
Figure 5.

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Stanford Exploration Project

4/20/1999