The main characteristics of volcanic tremor depend strongly on whether a volcano is erupting explosively and on the intensity of the event. Long before an eruption, tremor is ‘narrow-band’ (about 0.5–2 Hz and sometimes monochromatic or harmonic). On transitions to active volcanism, however, the maximum frequency can climb to 5–7 Hz (refs 1–4) (Fig. 1c and d). Moreover, whereas tremor related to low-intensity volcanism remains narrow-band, tremor associated with intermittent or protracted explosive behaviour is ‘broadband’, characterized by power distributed over the full 0.5–7 Hz tremor bandwidth.
When I read the above, I was not surprised that the tremors associated with volcanic activity were mainly comprised of low frequency components. What did surprise me was that there isn't more high frequency energy present in the measurements.
Is there a noticiable amount of high frequency activity in these tremors that is not significant enough to report, or are the higher frequency components absorbed by the crust surrounding the volcano?
- Jellinek, A.M. and Bercovici, D. (2011). Seismic tremors and magma wagging during explosive volcanism. Nature, 470, 522-526. [DOI]