Infrasonic waves and volcanic tremor at Stromboli

Abstract

The origin of the volcanic tremor is still under debate. Many theories have been proposed in the last years, but none has yet been completely accepted. In 1993, highly sensitive pressure sensors (2.175 Pa/Volt) used to monitor the explosive activity at Stromboli have revealed unexpected correlation between small spike‐shaped pressure signals (1–2 Pa) and volcanic tremor. These pressure pulses repeat regularly in time with a recurrent period of ca. 1 s. Video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents. The striking correlation (0.971) between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain. Infrasonic and seismic signal share the same spectral content (3 Hz) for every station within a range of 700 m around the craters. Correlations in time and frequency domain remained unaltered during the 1994 field experiments. Moreover, during 1994, the increased degassing activity has been followed by an increase in pressure release (7–8 Pa) and by a shift towards higher frequencies (8 Hz) both in the infrasonic and seismic records. Infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents, appearing therefore to be produced by the same dynamical process. On this basis, we claim that volcanic tremor at Stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column.

Monitoring methane emission of mud volcanoes by seismic tremor measurements: a pilot study

“…2) strongly mimics the shape of bubble bursting events detected from acoustic measurements at Stromboli volcano in Italy (e.g. Ripepe et al, 1996;Vergniolle et al, 1996).…”

Periodic volcanic degassing behavior: The Mount Etna example

“…Whilst there was no significant correlation between the raw data sets, a relevant correlation (R 2 > 0.6) was found in the (moving window) smoothed SO 2 flux and seismic rootmean-square (RMS) series, in particular, in the time intervals (shaded grey in Figure 3b), when the long-period SO 2 flux modulations (500-1200 s) are more prominent in the DT-CMWT (Figure 3c). We conclude, therefore, that these longer-period SO 2 flux modulations (e.g., those resolved by this smoothing window RMS procedure) are indeed volcanogenic in origin and most likely related to phases of more vigorous and sustained gas bubble bursting deep inside the NEC, given the previously established relationship between intense gas spattering and volcanic tremor [Ripepe et al, 1996].…”

On the volcanic waveguide

“…In addition, a strong acoustic signal may couple into the ground and be recorded by seismic stations [Ripepe et al, 1996;Garcds, 1995]. For the sake of brevity, the problem of ground-coupled air waves is relegated to a separate paper, and in this manuscript the acoustic and seismic propagation problems are treated separately.…”