1. Image Courtesy HVO Seimoacoustics from Kilauea Volcano using multiple arrays David Fee and Milton Garces Infrasound Laboratory Univ. of Hawaii, Manoa dfee@isla.hawaii.edu Tim Orr, David Wilson US Geological Survey Hawaiian Volcano Observatory

2. Image Courtesy HVO Overview Introduction to KilaueaIntroduction to Kilauea ArraysArrays Observations in Chronological OrderObservations in Chronological Order –Multiple types of tremor –Skylight Detection –Two fissure eruptions Acoustic energy vs. seismic/tilt eventAcoustic energy vs. seismic/tilt event ConclusionsConclusions

3. Image Courtesy HVO Pu`u` O`o Crater Complex Pu`u O`o crater complex is the active section of Kilauea VolcanoPu`u O`o crater complex is the active section of Kilauea Volcano Nearly continuous effusion and degassing from multiple vent system since 1992Nearly continuous effusion and degassing from multiple vent system since 1992 Lava flowed from the crater complex ~13 km through a complicated conduit system until it met the oceanLava flowed from the crater complex ~13 km through a complicated conduit system until it met the ocean Multiple open vents and lava tube skylights appear activeMultiple open vents and lava tube skylights appear active System changed in June 2007  fissure eruptionsSystem changed in June 2007  fissure eruptions

4. Image Courtesy HVO Infrasound Arrays – MENE MENE Array Semi-permanentSemi-permanent 12.5 km from Pu`u O`o12.5 km from Pu`u O`o Dense JungleDense Jungle Since 9/06Since 9/06

5. Image Courtesy HVO Infrasound Arrays – KIPU KIPU Array 2 week deployment in 4/072 week deployment in 4/07 2.5 km from Pu`u O`o2.5 km from Pu`u O`o High S/NHigh S/N Collocated BB SeisCollocated BB Seis

6. Image Courtesy HVO ZION Array Since 9/07Since 9/07 7 km from Pu`u O`o7 km from Pu`u O`o 6.5 km from Fissure D6.5 km from Fissure D Better azimuthal resolutionBetter azimuthal resolution Results preliminaryResults preliminary STC Seismometer Infrasound Arrays - ZION

7. Image Courtesy HVO Infrasonic Tremor for 12/1/2006 Usually constant between ~0.5-3 HzUsually constant between ~0.5-3 Hz Harmonic, gliding tremor as wellHarmonic, gliding tremor as well –Broad harmonics (~2 Hz) –High Attenuation? Gliding (spectral peaks change frequency over time)Gliding (spectral peaks change frequency over time) –Magma level may define effective length of conduit Seismic spectrogram from same period has relatively uniform tremor, some harmonicsSeismic spectrogram from same period has relatively uniform tremor, some harmonics Tremor not visible in waveformsTremor not visible in waveforms

8. Image Courtesy HVO KIPU results – Tremor and Skylight PMCC Detections:PMCC Detections: 4/22/07 1510-1525 Nearly all signal originated from Pu`u O`oNearly all signal originated from Pu`u O`o Discovered skylight along lava tube systemDiscovered skylight along lava tube system –Intermittently acoustic active, both audible and infrasound Possible to discriminate between the two sourcesPossible to discriminate between the two sources Need confirmation of detection…Need confirmation of detection… KIPU

9. Image Courtesy HVO KIPU results – 4/22/07 0600-0800 UTC A sharp, complex spectral peak of ~0.6 Hz is present at KIPU and MENEA sharp, complex spectral peak of ~0.6 Hz is present at KIPU and MENE Tends to bifurcate and shift frequency over timeTends to bifurcate and shift frequency over time Seismic wavefield is complex and path effects appear to be present, but spectral peak is also manifestedSeismic wavefield is complex and path effects appear to be present, but spectral peak is also manifested Broadband infrasound signal as wellBroadband infrasound signal as well Black-2.5 km inf Red-13 km inf Blue-seismic

10. Image Courtesy HVO Episode 56 EQ swarm begins around 6/17 1415 UTC on upper east rift zone near Mauna UluEQ swarm begins around 6/17 1415 UTC on upper east rift zone near Mauna Ulu –Magma intrusion 1.5-3 km deep Puu Oo Vent collapses on 6/18Puu Oo Vent collapses on 6/18 First impulsive acoustic events at Puu OoFirst impulsive acoustic events at Puu Oo Relatively long durationRelatively long duration

11. Image Courtesy HVO Episode 56 – Fissure Opening Infrasound signals around 1015-1045 UTC from ~132°Infrasound signals around 1015-1045 UTC from ~132° Fissure Opening?Fissure Opening? Fissure Opening?

12. Image Courtesy HVO Episode 56 - Resuts 200 m long fissure opens 6 km west of on 6/19200 m long fissure opens 6 km west of on 6/19 –Steam, gas, and lava Infrasound recordings from 0900-1100 UTC pm 6/19Infrasound recordings from 0900-1100 UTC pm 6/19 –Focused between 2-10 Hz, doesn’t look like surf or cultural –Not constrained well by any other technology –Harmonics present –Similar to Puu Oo

13. Image Courtesy HVO Fissure Eruption – 7/21/2007 Magma drained from Pu`u O`o around 1000 UTCMagma drained from Pu`u O`o around 1000 UTC Eruption moved eastward along a set of fissures – strong infrasound!Eruption moved eastward along a set of fissures – strong infrasound! Seismically quiet, video blocked by poor weatherSeismically quiet, video blocked by poor weather

14. Image Courtesy HVO Fissure Eruption- 8/22/07 Increased tremor signals in late AugustIncreased tremor signals in late August Activation of harmonics around 2000 UTCActivation of harmonics around 2000 UTC Increased activity prompted installation of second array in GlenwoodIncreased activity prompted installation of second array in Glenwood

15. Image Courtesy HVO Fissure Eruption – 7/21/2007: Single array Fissure signal concentrated between 1.5-5 Hz, similar to Puu OoFissure signal concentrated between 1.5-5 Hz, similar to Puu Oo No harmonicsNo harmonics

16. Image Courtesy HVO ZION Results – 2007/9/17 Tremor signals switch on to Puu Oo on 9/17?Tremor signals switch on to Puu Oo on 9/17? Puu Oo still actively degassingPuu Oo still actively degassing Standing HypothesisStanding Hypothesis –Magma interacting with the gas –Many ways of producing this process –Want to model broad spectral peak FD PO

17. Image Courtesy HVO Daily Acoustic Energy Calculation Calculate acoustic source energy for tremorCalculate acoustic source energy for tremor To differentiate between signal and noise, the acoustic energy is only calculated during times of coherent signal from the specified azimuth.To differentiate between signal and noise, the acoustic energy is only calculated during times of coherent signal from the specified azimuth. Split data into 60 sec windowsSplit data into 60 sec windows Mean correlation value for window must be above thresholdMean correlation value for window must be above threshold Minimum number of pixels per windowMinimum number of pixels per window Fissure Eruptions E Acoustic =2πr 2 /ρc ∫ΔP(t) 2 dt r=source-receiver distance ρ=air density C=sound speed ΔP=change in pressure

18. Image Courtesy HVO Acoustic Energy vs. RSAM/Tilt Event 1: 8/24 00:02 UTC (8/23 14:02 HST)Event 1: 8/24 00:02 UTC (8/23 14:02 HST) Collapse Event:Collapse Event: –Significant drop-off in acoustic energy (tremor) in the days following this collapse event. –Event preceded by 3 days of high acoustic tremor and RSAM values. –No impulsive acoustic signal recorded at the time of the seismic/tilt event. Minor earthquake recorded by the infrasound sensors around 0000 UTC. –Collapse event may have changed magma/degassing dynamics.

19. Image Courtesy HVO Acoustic Energy vs. RSAM/Tilt Event 2: 8/29 1100-1400 UTC (8/29 0100-0400 HST)Event 2: 8/29 1100-1400 UTC (8/29 0100-0400 HST) Tremor EventTremor Event –Strong acoustic and seismic tremor during this 3 hour time period, originating from P‘u‘u ‘O‘o, not Fissure D. –Infrasound signal concentrated between 1220-1400 UTC, is below 3 Hz, Collapse event may have changed magma/degassing dynamics. –Infrasound signal decreased rapidly at 1400 UTC and returns to similar azimuth as Fissure D. –No longer-term variation in acoustic energy or RSAM apparent. –Similar “burst” of tremor occurred on 9/17 around 0900 UTC.

20. Image Courtesy HVO Acoustic Energy vs. RSAM/Tilt Event 3: 9/3 0152 UTC (9/2 1552 HST)Event 3: 9/3 0152 UTC (9/2 1552 HST) Collapse Event:Collapse Event: –Nothing out of the ordinary recorded acoustically at the time of this collapse event. –However, tremor energy levels decreased to near zero in the days following. Collapse event may have changed dynamics as well.

21. Image Courtesy HVO Conclusions – Future Work Identification of new sources (skylight, fissures) made at KilaueaIdentification of new sources (skylight, fissures) made at Kilauea Tremor observations consistent with pressure oscillations resulting from unsteady magma flow within tubes/conduitsTremor observations consistent with pressure oscillations resulting from unsteady magma flow within tubes/conduits P‘u‘u ‘O‘o tremor between 0.5 – 3 Hz fairly constant in both infrasound and seismic recordings before 6/18P‘u‘u ‘O‘o tremor between 0.5 – 3 Hz fairly constant in both infrasound and seismic recordings before 6/18 Higher frequency harmonic, gliding tremor more intermittent and possibly due to excitation of conduitHigher frequency harmonic, gliding tremor more intermittent and possibly due to excitation of conduit Sharp spectral peaks in infrasound and seismic – same resonating source?Sharp spectral peaks in infrasound and seismic – same resonating source? Comparison of seismic, infrasound, and tilt data help explain dynamics and overall volcanic activity levelsComparison of seismic, infrasound, and tilt data help explain dynamics and overall volcanic activity levels