The three seismograms above show vertical earth velocity on the pier of the walk-in underground vault near Leonard Oklahoma. The middle trace is the unfiltered output of the seismometer. It shows P, S and LR (LR are surface Rayleigh waves). It also shows SS (S reflected from the earths surface midway between the epicenter and Leonard) and SSS (S reflected twice from the surface). The top trace is the same seismogram filtered to pass only waves with frequencies between 0.5 and 2.0 Hertz. This shows only the P (longitudinal, or push-pull, or primary) seismic waves. Many seismographs are designed to only pick up these higher frequency P waves. The bottom trace is the same as the middle trace except that it is filtered to only pass waves with frequencies below 0.01 Hertz. These extremely low frequency waves vibrate the ground so slowly that the time from one peak to another peak is 100 seconds or more.
The above seismograms show ground velocity recorded by the OGS in vertical, radial (toward the epicenter), and transverse (at right angles to the direction of the epicenter) directions. Each trace is lowpass filtered to show only waves with a period of 100 seconds or more. The P arrival is off the figure. S is clear on all traces. When the traces are rotated to produce vertical, radial, and transverse motion, the two types of surface waves are completely separated. Rayleigh waves (LR) show only on the vertical and radial traces. The earlier arriving Love (LQ) waves only show on the transverse seismogram. The vertical LR ground motion was about 3.8 millimeters peak-to-peak, at the underground vault near Leonard. This allowed the OGS to calculate an MW type magnitude of 7.8. It might seem that if the earth's surface in Oklahoma moved up and down four millimeters, that buildings would be damaged. There would be damage if the movement was rapid. However, the movement was like slowly lifting the earth over a minute or so, then lowering it as slowly. Such slow motion will not effect anything but the detection sensor of a very broadband seismometer.
The Rayleigh surface wave from the 1999 AUG17 earthquake, had both up-down and radial (toward and away from the epicenter) motion. The above is a particle motion plot showing how the earth moved along a vertical plane with the laft edge pointing toward the epicenter. The figure was generated using 450 seconds from the 100 second vertical and radial seismograms in the previous figure. Rayleigh waves move in an ellipse (nearly a circle in this case). When the ground is at its highest point, it is moving toward the epicenter, away from the direction the wave is moving. Ocean or lake waves, or the ripples in a glass of liquid, move in a similar fashion, but the motion at the high point is in the same direction the wave is moving.