1. 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

2. Study motivation and goals Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Need for greater constraint on shallow conduit processes at 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 Locate the source of very long period (VLP) signals Model the geometry of the VLP source Model the geometry of the VLP source Explore shallow conduit dynamics with SO 2 and tilt Explore shallow conduit dynamics with SO 2 and tilt

3. Study site and experimental setup 10 broadband seismometers (60 and 30 s corner) 10 broadband seismometers (60 and 30 s corner) 8 infrasound sensors (50 s corner) 8 infrasound sensors (50 s corner) UV camera (~1 Hz sample rate) UV camera (~1 Hz sample rate) 19 days of recording 19 days of recording strombolian activity strombolian activity Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion

4. Seismic and acoustic data Infrasound 10 – 30 s 0.5 – 10 Hz

5. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Repeating VLP signals

6. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion VLP particle motion

7. Synthetic Green’s functions 3-D finite difference method (Ohminato and Chouet, 1997) Synthetic Green’s functions 3-D finite difference method (Ohminato and Chouet, 1997) 11.7 x 9 x 6 km computational space 11.7 x 9 x 6 km computational space 600 x 240 x 1080 m source volume (40 m mesh) 600 x 240 x 1080 m source volume (40 m mesh) 30 – 10 s period 30 – 10 s period Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Full waveform inversion

8. Synthetic VLP waveforms 6 moment component best fit source (240 m west, 380 m below summit crater) 6 moment component best fit source (240 m west, 380 m below summit crater) Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion F900 F9A F9SW

9. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Source time function Point by point eigenvector analysis suggests a stable source mechanism Point by point eigenvector analysis suggests a stable source mechanism

10. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Forward modeling to constrain source geometry Single crack dominates forward models Single crack dominates forward models Sill-like geometry dipping 30° southwest Sill-like geometry dipping 30° southwest Forces would produce 2000 m 3 volume change in a sill Forces would produce 2000 m 3 volume change in a sill

11. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion VLP source location Sill located 240 m west, 380 m below summit dipping 30° southwest Sill located 240 m west, 380 m below summit dipping 30° southwest Location and geometry suggest old lava flow may control shallow conduit geometry Location and geometry suggest old lava flow may control shallow conduit geometry

12. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion Tilt signal accompanies explosions Apparent tilt derived from seismic data Apparent tilt derived from seismic data Positive tilt away from summit crater 4-6 minutes prior to explosions Positive tilt away from summit crater 4-6 minutes prior to explosions

13. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion UV camera SO 2 emissions UV images reveal 2 active vents UV images reveal 2 active vents Decrease in SO 2 prior to explosions Decrease in SO 2 prior to explosions [Nadeau et al., JGR, 2010]

14. UV camera SO 2 emissions Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion

15. Conclusions and future work Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusions VLP source located 240 m west and 380 m below summit crater VLP source located 240 m west and 380 m below summit crater Forward modeling suggests sill-like source dipping 30° southwest Forward modeling suggests sill-like source dipping 30° southwest Radial tilt and decreasing SO 2 recorded prior to explosions Radial tilt and decreasing SO 2 recorded prior to explosions Sealing or annealing of the conduit traps gas that drives explosions Sealing or annealing of the conduit traps gas that drives explosions Need to invert more VLP signals to test source location and geometry Need to invert more VLP signals to test source location and geometry Compare seismic VLP to infrasound VLP Compare seismic VLP to infrasound VLP Deployment of tilt meters in future experiments Deployment of tilt meters in future experiments

16. Motivation Study site VLP data Waveform Inversion Tilt data SO 2 emissions Conclusion

17. Inversion results