Question

PLEASE HELP ME!!!

Answer 1

The reason for that is that P-waves (primary waves) travel faster than S-waves (secondary waves).

If we call $v_p$ the speed of the primary waves and $v_s$ the speed of the secondary waves, and we call $S$ the distance of the seismogram from the epicenter, we can write the time the two waves take to reach the seismogram as
$t_P = \frac{S}{v_P}$
$t_S= \frac{S}{v_S}$

So the lag time between the arrival of the P-waves and of the S-waves is
$\Delta t = t_S-t_P= \frac{S}{v_S}- \frac{S}{v_P}= S(\frac{1}{v_S}- \frac{1}{v_P})$
We see that this lag time is proportional to the distance S, therefore the larger the distance, the greater the lag time.