[jboot]

Thanks for the reference. Harmonic tremor is sometimes but not always associated with magma movement. From the same link you sent me there is also a discussion and graphic of "Shallow Volcanic Earthquakes". For reference, here's the graphic:

Now, this is by no means diagnostic, but I've been clicking around a bit on the USGS siesmology site and comparing some of the recent larger tremors in the swarm to this graphic. Many of the waveforms appear to conform to the "shallow volcanic" sample. For instance, check out the siesmogram of Event nn00333644 from earlier today:

[Godzilla]

Thats fine, now look at the estimated depth - 0 km. Is there an eruption occuring? No.

Look again to your figure posted. Note the roughly equal amplitude of the harmonics vs the varying amplitudes of the other examples. Now look at the seismographs that are the closest to the event. Note the sharpness, while the ones you may consider to represent a ‘shallow volcanic earthquake’ are farther away. The difference? Attenuation of the wave over distance and interference by the various waves and other sources.

Again, 0 km - yet no eruption.

[Godzilla]

Harmonic tremor is sometimes but not always associated with magma movement.

You said only eruptions - whats moving? Magma, what else causes similar waveforms?