Sealing the deal? A seismic source model for strombolian explosions at

Fuego volcano, Guatemala

John Lyons (jlyons@mtu.edu)

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

Infr

asou

nd

10

– 30

s

0.5

– 10

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