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.
The Helicorders and webicorders do not record harmonic tremors quite like that which we are familiar with via regular seismograph signatures.
These events are captured as such on a webicorder.
http://i710.photobucket.com/albums/ww109/volcanism2/alaska/REF_2009-03-26.jpg
Note before Redoubt's first large eruption in March and throughout Feb. of last year, harmonic tremors were more the norm than the swarms you see on that graph prior to eruption. The harmonics oscillated as well but you can clearly see their signature on the webicorder.
The first large one at the top of graph led to a medium size expulsion of ash and vapor. More importantly, a series of harmonics started the quake swarm right before the first large explosive event.
