Total time required for seismic wave to travel through the rock towards the seismic receiver:
| (1) | T^2_x = T^2_0 + \frac{4 x^2}{V^2_{rms}} |
where
x is lateral offset between the seismic source and seismic receiver,
T^2_0 is reflection time at zero offset (which means the normal incident wave reflection),
V_{rms} – average p-wave speed through the reflecting travel distance between the seismic source and seismic sensor:
| V^2_{rms} = \frac{\sum_i^N V_p^2(t_i) \, \delta t_i}{\sum_i^N \delta t_i}= \frac{\sum_i^N V_p(t_i) \, \delta h_i}{\sum_i^N \frac{\delta h_i}{V_p(t_i)}} |
where
V_p(t_i) is p-wave velocity of rocks found at travel time t_i,
\delta t_i is travel time through the rock element of thickness \delta h_i in tghe rock element found at travel time t_i.