Seismic refraction – single horizontal interface

Seismic refraction – single horizontal interface

 

 The P-wave is refracted at the interface between the two layers. Since v1 > v2 the wave is refracted towards the horizontal. As the angle of incidence is increased, the geometry results in a head wave travelling horizontally in layer 2. From Snell’s Law we can write: 

 

 

 

 

                                                                       

• The travel time curve for the refracted wave is a straight line with slope = 1 / v2
• The refracted arrival is only observed when x > xcrit = 2z tan cθ
• The refracted wave is the first arrival at values of x greater than the cross over distance (xcross)
• When x = xcrit the refracted and reflected waves are the same
• v2 can be calculated from the slope of the refracted wave on the t-x plot                  
• The depth of the interface (z) can be found by extrapolating the travel time of the refracted wave to x = 0 where the travel time is