That would be a secondary, or 'S' wave. Moving in a snakelike movement, this wave has to travel a farther distance, so it takes longer to reach the recording equipment.
a siesmic wave is a wave that travels through the earth. there are two MAIN types, P and S waves. a siesmograph shows the type of wave and how far away it is from that point.
s wave
L waves are formed when P&S waves reach the surface.
These are known as the seismic waves or the s waves. They will reach the earthquake location second after the first shock.
Surface waves
L waves are formed when P&S waves reach the surface.
S waves
The Secondary or S-wave.
A surface wave is the last seismic wave to arrive after an earthquake.
"1 Hz" means that 1 complete wave passes the place where you're sitting each second. So regardless of what kind of wave it is or what its speed may be, if its frequency is 1 Hz, then it takes 1 second to travel 1 wavelength.
The standard unit for ANY type of frequency is the Hertz - cycles per second. Its dimensions are (1 / second).
It is a type of mechanical wave known as a seismic wave.