Body waves from distant earthquakes
travel a curving path through the earth arriving at seismic stations from below.
The compressive motion of a P-wave is in the direction the wave travels, thus the
motion of the seismometer will be mostly vertical with little horizontal motion.
The S wave has a shearing motion perpendicular to the ray path, thus the S
wave produces chiefly horizontal movement. Surface waves travel in an undulating
pattern across the surface of the Earth producing up-down back forth
side-to-side motion. The seismogram merely depicts motion, not direction of
motion. The movement of the building is exaggerated to show the relative motion of each wave only detectable by seismometers of this distance