[Steve Van Doorn]

This is Seismogram of harmonic tremor recorded on seismic station RAN on April 2, 1980. saint Helen:

[Godzilla]

Yes it is - about 1/2 way down from the top. Go to the link I provided you - you will see the constant, long period wave

Now find the similar one in your picture. In fact my link and picture above are taken from the very image you posted - right there in the middle. The shorter, higher amplitude waves are not harmonic tremors.

But then don't take my professional word on it as a geologist - nor the professional word of those who have made it their career to study it.