ERSC 3V93 Lecture Notes - Lecture 47: Seismology, The Intercept, Reflection Seismology
4 May 2016
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Critical distance: xcrit - distance at which first head wave arrives at surface, xcross - is point at which headwave overtakes direct wave. Simple two-layer case with v2 > v1 and a planar horizontal interface: direct wave from a to d travels at velocity v1, head wave travels down to refractor along slant paths. Ab and cd at velocity v1: travels along refractor bc at velocity v2. The travel time of the head wave is obtained by dividing the ray path segments by their respective velocities: distance/velocity = m/ms-1 = s travel-time equation can be. The reformulated into a more useful form using sin = v1/v2 and trig identities: re-write eq. in terms of x, v1, v2. The travel time equation is straight line with slope 1/v2 andintercept ti. The intercept term is rearranged and solved for depth: valid only for planar, horizontal refractor, depth usually assigned to first shot point.
