Gillian Sharer accepted answer staff Nov. 14, 2013, 1:54 p.m.
Earth tides can be seen at most of the coastal TA stations using an appropriate filter. Very long period noise, siting far inland, and/or vault instabilities at a site are possible reasons why Earth tides may not be observed. See the attached images for more information, which compare an earth tide signal signature on the LHZ channel at GSN network station KDAK on Kodiak Island, Alaska, USA with an earth tide signal signature on the LHZ channel at TA station I64A at Boothbay, Maine, USA. Both signals have been demeaned and have a low-pass filter applied.
Figure 3 below shows this in even more detail for station TA_I64A on the LHZ channel: