There is a constant vibration in teh earth with a dominant period of 6 seconds called the "microseismic peak". This is caused by the interactions of oceanic swells with the continental shelf, the amplitude of this signal will vary with the seasons (and the size of the waves in the North Atlantic). You should be able to see this microseismic 6sec peak in a spectrum of your data. If the peak amplitude of your noise spectrum is not at about 6 seconds then this is a good indication that something is wrong with your setup.
pdenton, 24-Feb-2008 08:57 (GMT)