Seimoacoustics from kilauea volcano using multiple arrays
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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

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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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