S–P time
= S–P time
{c}
{title2=$\Delta t=t_S-t_P$}
The delay between corresponding <S wave> and <P wave> arrivals. For a common uniform path of length $r$, $\Delta t=r(1/V_s-1/V_p)$, cancelling <earthquake origin time>. Matched phase identification and an appropriate <velocity model> are needed to infer distance.