circular reasoning - the science of EQs

All EQ waves are not created equal.

P-Waves are faster than S-Waves

time delay

so the P-Waves get to the seismograph first.
And there is a wait for the S-Waves to arrive.

time = distance

the farther away the quake -- the longer the delay.
Ahh - time = distance.

distance = radii

once the distance is known -- a circle can be drawn with your laboratory at its center, and this distance as the radius.

i'll get by with a little help from my friends

and when two other friends tell you how far away the quake occurred from their laboratory --- the site of the EQ can be plotted.

The three circles intersect at the EQ site.