Answer:
in a perpendicular direction
Step-by-step explanation:
The shear wave or S wave (from secondary wave) is the one that is produced after an Earthquake produces the principal wave (P), and this S wave travel in opposite direction and with a slower velocity.
That is the reason why the apparatus first detect the P wave and then the S wave.
They can travel trough rocks but with less energy and less velocity.
Hope this info is useful.