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Sealing the deal? A seismic source model for strombolian explosions at Fuego volcano, Guatemala. John Lyons ([email protected]) Greg Waite Tricia Nadeau 17 December 2010 AGU Fall Meeting . PIRE 0530109. - PowerPoint PPT Presentation
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Sealing the deal? A seismic source model for strombolian explosions at
Fuego volcano, Guatemala
John Lyons ([email protected])
Greg Waite Tricia Nadeau
17 December 2010 AGU Fall Meeting
PIRE 0530109
Study motivation and goals
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
• Need for greater constraint on shallow conduit processes at open vent volcanoes lacking dense monitoring networks
• Locate the source of very long period (VLP) signals
• Model the geometry of the VLP source
• Explore shallow conduit dynamics with SO2 and tilt
Study site and experimental setup
• 10 broadband seismometers (60 and 30 s corner)
• 8 infrasound sensors (50 s corner)
• UV camera (~1 Hz sample rate)
• 19 days of recording
• strombolian activity
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Seismic and acoustic data
Infra
soun
d
1
0 –
30 s
0.5
– 1
0 Hz
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Repeating VLP signals
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
VLP particle motion
• Synthetic Green’s functions 3-D finite difference method (Ohminato and Chouet, 1997) • 11.7 x 9 x 6 km computational space• 600 x 240 x 1080 m source volume (40 m mesh)• 30 – 10 s period
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Full waveform inversion
Synthetic VLP waveforms• 6 moment component best fit source (240 m west, 380 m below summit crater)
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
F900F900 F9AF9SW
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Source time function
• Point by point eigenvector analysis suggests a stable source mechanism
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Forward modeling to constrain source geometry• Single crack dominates forward models • Sill-like geometry dipping 30° southwest• Forces would produce 2000 m3 volume change in a sill
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
VLP source location• Sill located 240 m west, 380 m below summit dipping 30° southwest• Location and geometry suggest old lava flow may control shallow conduit geometry
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Tilt signal accompanies explosions• Apparent tilt derived from seismic data• Positive tilt away from summit crater 4-6 minutes prior to explosions
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
UV camera SO2 emissions• UV images reveal 2 active vents• Decrease in SO2 prior to explosions
[Nadeau et al., JGR, 2010]
UV camera SO2 emissions
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Conclusions and future work
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusions
• VLP source located 240 m west and 380 m below summit crater• Forward modeling suggests sill-like source dipping 30° southwest• Radial tilt and decreasing SO2 recorded prior to explosions• Sealing or annealing of the conduit traps gas that drives explosions
• Need to invert more VLP signals to test source location and geometry• Compare seismic VLP to infrasound VLP• Deployment of tilt meters in future experiments
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion
Inversion results