John Lyons (jlyons@mtu) Greg Waite Tricia Nadeau 17 December 2010 AGU Fall Meeting

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. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Study motivation and goals • 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

3. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion 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

4. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Seismic and acoustic data Infrasound 10 – 30 s 0.5 – 10 Hz

5. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Repeating VLP signals

6. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion VLP particle motion

7. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Full waveform inversion • 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

8. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Synthetic VLP waveforms • 6 moment component best fit source (240 m west, 380 m below summit crater) F900 F900 F9A F9SW

9. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Source time function • Point by point eigenvector analysis suggests a stable source mechanism

10. Motivation Study siteVLP dataWaveform 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

11. 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

12. Motivation Study siteVLP dataWaveform 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

13. Motivation Study siteVLP 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]

14. Motivation Study siteVLP data Waveform Inversion Tilt data SO2 emissions Conclusion UV camera SO2 emissions

15. Motivation Study siteVLP data Waveform Inversion Tilt data SO2 emissions Conclusions Conclusions and future work • 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

16. Motivation Study site VLP data Waveform Inversion Tilt data SO2 emissions Conclusion

17. Motivation Study siteVLP dataWaveform Inversion Tilt data SO2 emissions Conclusion Inversion results