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Seimoacoustics from Kilauea Volcano using multiple arrays. David Fee and Milton Garces Infrasound Laboratory Univ. of Hawaii, Manoa [email protected] Tim Orr, David Wilson US Geological Survey Hawaiian Volcano Observatory. Overview. Introduction to Kilauea Arrays

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seimoacoustics from kilauea volcano using multiple arrays
Seimoacoustics from Kilauea Volcano using multiple arrays

David Fee and Milton Garces

Infrasound Laboratory

Univ. of Hawaii, Manoa

[email protected]

Tim Orr, David Wilson

US Geological Survey

Hawaiian Volcano Observatory

overview
Overview
  • Introduction to Kilauea
  • Arrays
  • Observations in Chronological Order
    • Multiple types of tremor
    • Skylight Detection
    • Two fissure eruptions
  • Acoustic energy vs. seismic/tilt event
  • Conclusions
pu u o o crater complex
Pu`u` O`o Crater Complex
  • Pu`u O`o crater complex is the active section of Kilauea Volcano
  • Nearly 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 ocean
  • Multiple open vents and lava tube skylights appear active
  • System changed in June 2007  fissure eruptions
infrasound arrays mene
Infrasound Arrays – MENE

MENE Array

  • Semi-permanent
  • 12.5 km from Pu`u O`o
  • Dense Jungle
  • Since 9/06
infrasound arrays kipu
Infrasound Arrays – KIPU

KIPU Array

  • 2 week deployment in 4/07
  • 2.5 km from Pu`u O`o
  • High S/N
  • Collocated BB Seis
infrasound arrays zion

STC Seismometer

Infrasound Arrays - ZION

ZION Array

  • Since 9/07
  • 7 km from Pu`u O`o
  • 6.5 km from Fissure D
  • Better azimuthal resolution
  • Results preliminary
infrasonic tremor for 12 1 2006
Infrasonic Tremor for 12/1/2006
  • Usually constant between ~0.5-3 Hz
  • Harmonic, gliding tremor as well
    • Broad harmonics (~2 Hz)
    • High Attenuation?
  • 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 harmonics
  • Tremor not visible in waveforms
kipu results tremor and skylight

KIPU

KIPU results – Tremor and Skylight
  • PMCC Detections:

4/22/07 1510-1525

  • Nearly all signal originated from Pu`u O`o
  • Discovered skylight along lava tube system
    • Intermittently acoustic active, both audible and infrasound
  • Possible to discriminate between the two sources
  • Need confirmation of detection…
kipu results 4 22 07 0600 0800 utc
KIPU results – 4/22/07 0600-0800 UTC
  • A sharp, complex spectral peak of ~0.6 Hz is present at KIPU and MENE
  • Tends to bifurcate and shift frequency over time
  • Seismic wavefield is complex and path effects appear to be present, but spectral peak is also manifested
  • Broadband infrasound signal as well

Black-2.5 km inf

Red-13 km inf

Blue-seismic

episode 56
Episode 56
  • EQ 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 6/18
  • First impulsive acoustic events at Puu Oo
  • Relatively long duration
episode 56 fissure opening

Fissure Opening?

Episode 56 – Fissure Opening
  • Infrasound signals around 1015-1045 UTC from ~132°
  • Fissure Opening?
episode 56 resuts
Episode 56 - Resuts
  • 200 m long fissure opens 6 km west of on 6/19
    • Steam, gas, and lava
  • Infrasound 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
fissure eruption 7 21 2007
Fissure Eruption – 7/21/2007
  • Magma drained from Pu`u O`o around 1000 UTC
  • Eruption moved eastward along a set of fissures – strong infrasound!
  • Seismically quiet, video blocked by poor weather
fissure eruption 8 22 07
Fissure Eruption- 8/22/07
  • Increased tremor signals in late August
  • Activation of harmonics around 2000 UTC
  • Increased activity prompted installation of second array in Glenwood
fissure eruption 7 21 2007 single array
Fissure Eruption – 7/21/2007: Single array
  • Fissure signal concentrated between 1.5-5 Hz, similar to Puu Oo
  • No harmonics
zion results 2007 9 17

PO

FD

ZION Results – 2007/9/17
  • Tremor signals switch on to Puu Oo on 9/17?
  • Puu Oo still actively degassing
  • Standing Hypothesis
    • Magma interacting with the gas
    • Many ways of producing this process
    • Want to model broad spectral peak
daily acoustic energy calculation

Fissure Eruptions

Daily Acoustic Energy Calculation
  • Calculate 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.
  • Split data into 60 sec windows
  • Mean correlation value for window must be above threshold
  • Minimum number of pixels per window

EAcoustic=2πr2/ρc ∫ΔP(t)2dt

r=source-receiver distance

ρ=air density

C=sound speed

ΔP=change in pressure

acoustic energy vs rsam tilt
Acoustic Energy vs. RSAM/Tilt
  • Event 1: 8/24 00:02 UTC (8/23 14:02 HST)
  • 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.
acoustic energy vs rsam tilt1
Acoustic Energy vs. RSAM/Tilt
  • Event 2: 8/29 1100-1400 UTC (8/29 0100-0400 HST)
  • Tremor 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.
acoustic energy vs rsam tilt2
Acoustic Energy vs. RSAM/Tilt
  • Event 3: 9/3 0152 UTC (9/2 1552 HST)
  • 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.
conclusions future work
Conclusions – Future Work
  • Identification of new sources (skylight, fissures) made at Kilauea
  • Tremor 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 6/18
  • Higher frequency harmonic, gliding tremor more intermittent and possibly due to excitation of conduit
  • Sharp spectral peaks in infrasound and seismic – same resonating source?
  • Comparison of seismic, infrasound, and tilt data help explain dynamics and overall volcanic activity levels
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