The above seismogram was recorded at one sample per second from a Geotech KS54000-0103 broadband seismometer at 119 meter depth in the Glastnost Borehole near Leonard, Oklahoma. The trace represents vertical ground acceleration. On the top unfiltered trace (black), the large M shaped curves are the solid earth tides. Like Ocean tides, earth tides are caused by the gravitational attraction of the sun and moon, which, at any given location, changes as the earth rotates. Several earthquakes show up as spikes. The earthquake's individual waves are only seen if the trace is spread out. The Ocean generated microseisms, with a repitition period of only about six seconds, are different from tides, which repeat in 12 hours and 20 minutes. The constant up and down of oceanic microseisms thickens the tide trace into a band. The second (middle, green) trace, is the top trace with all motion with a period less than 1000 seconds (or a frequency greater than 0.001 Hertz) filtered out. This leaves only tides and long period free vibrations of the earth. This trace shows almost exclusively earth tides. The tidal curve changes in shape as the phase of the moon changes. The bottom (light blue) trace is the top trace filtered to pass only 100 second to 20 second period (0.01 Hz. to 0.05 Hz. frequency) waves characteristic of earthquakes. Five earthquakes are labeled with their location and magnitude.
On this and the next figure, the unfiltered tide trace is blue instead of black. Only a short portion of the first figure is shown, to make the Northern Colombia earthquake clearer, and show two additional earthquakes. The green (earth tide) trace is "bumpy". The bumps are possibly free vibrations of the entire earth, excited by the four magnitude 6 or larger earthquakes shown in the first figure.
This figure includes top and bottom traces, but not the middle tide trace. It is zoomed in to show some individual waves from the Northern Colombia earthquake. Four identified phases (arrivals) are identified on the bottom trace.