Fig 1. Schematic cartoon illustrating how the total amplitude decay of the recorded signal is composed of an intrinsic and radiative part.(Equation: Aki et al. 1977)

Fig 2. Output from finite-difference model illustrating the depth-dependence of the frequency content. At each depth level, the spectrum of a synthetic seismogram is plotted, clearly illustrating a resonance, with a fundamental and harmonic overtones, due to interface waves at the conduit walls.

Fig 4. Results of apparent Q of the synthetic signals from varying the intrinsic Q inside the conduit (for a fixed geometry and parameter contrast and hence, fixed radiative Q). Two regimes are identifiable: 1. Where the apparent Q is greater than the intrinsic Q and resonance dominates and 2. Where the apparent Q is less than the intrinsic Q and radiative energy loss dominates. These two regimes highlight the competing effects of energy trapping due to the resonance and dissipation of the energy due to radiative losses.

Fig 5. Families of low-frequency events classified by similar waveforms (Green & Neuberg 2006). Family 'A' is the dominant family before the dome collapse, which occurred at around 12:45pm local time on the 25th June 1997(dashed red line). Due to the large number of events (~3000) and largest amplitudes, family 'A' events were chosen as the first target for investigation and obtaining apparent Q values.

Fig 6. Amplitude spectra for all family 'A' events preceding the dome collapse, shown in temporal order. The dashed lines represent the swarm boundaries ( see Fig 5.). The events have been first band-pass filtered between 0.5 and 5Hz. The events show remarkable consistency of spectral peaks across both individual swarms and across the whole period of several days. This indicates that the they are caused by a common resonating source body that remains stable, in terms of both geometry and magma properties, throughout the whole time period.