6:15 PM - 7:30 PM
[SVC46-P12] Variation of VLP signals accompanying eruptions at Stromboli volcano, Italy
Keywords:Strombolian eruptions, VLP, explosion earthquakes
We have conducted broadband seismic observation at Stromboli volcano since May 2014. From 4 month long broadband seismic record, most VLP events seem to have similar waveform characteristics mentioned in Chouet et al. (2003) (inflation-deflation-inflation sequence). However, we recognized there are several waveform types prior to main first inflation phase.
1. Gradual inflation (10 ~ 30 sec) prior to main inflation
2. Having small deflation phase (~ 5 sec) during gradual inflation (type 1)
3. Gradual deflation (10 ~ 30 sec) prior to main inflation
4. Combination of type 2 and 3
5. Short deflation (~ 5 sec) prior to main inflation
6. No main inflation phase (Only downward pulse)
As described above, there are certain groups of VLP events which have deflation phase prior to main first inflation phase. Even if amplitude of deflation phase is small, such deflation process cannot be explained by the simple gas slug rising model. Moreover, some VLP events (type 6) have no inflation phase at the onset. Particle motion analysis for onset and first inflation phase shows events in type 1, 2, 5, 6 have common azimuthal direction (NW-SE direction), while events in type 3, 4 have slightly different direction. Since Stromboli volcano has several active vents on the northwest direction from our seismic station, these differences of azimuthal motions may reflect the difference of vents where eruptions were taken place. Another remarkable feature is about the transition of occurrence frequency of each type. For example, occurrence frequency of type 6 has decreased at the beginning of Aug. 2014. Those days correspond to the period that amplitude of RMS (root-mean-square) of high frequency (> 3 Hz) has decreased. Also transition of eruption style has been reported at that period, from intermittent Strombolian eruptions to lava outflow and effusive eruptions.