Ocean Infrasound

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Ocean Infrasound
M. Garces (for UH, UM, NRL, BBN) University of
Hawaii, Manoa
Second NSF Infrasound Workshop, June 8, 2005
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Preliminary Partitioning of Ocean Infrasound
Tsunamis
Wind Advection
Surf
Swell Size
Quake-induced vibrations
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Surf Infrasound BBN-UH Collaboration
Makalawena Beach, Hawaii Rocky coastline, small
surf
Polihale Beach, Kawaii Shorebreak, huge surf
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Surf Infrasound BBN-UH Collaboration
Makalawena Beach, Hawaii Surf interaction with
rocky shoreline produces infrasound, closest
source dominates
Polihale Beach, Kawaii Barrels produce infrasound!
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(No Transcript)
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Surf Infrasound Polihale data set
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Surf Infrasound Concluding Remarks

• Infrasound is generated by waves breaking
  against rocky shorelines and cliffs water-solid
  interactions
• Infrasound is also produced by a barreling wave,
  or by fluid-fluid interactions (water-gas,
  water-water)
• Infrasonic amplitude is correlated with ocean
  wave height and possibly wave type
• Frequency content much higher than initially
  thought
• Need source models!

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Microbaroms Horizontal radiationMicroseisms
Vertical radiation
Wind
Swell Size
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Ocean waves are driven by surface winds
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Microbarom, 10-20 km wind (blue) and 50-70 km
wind (red) azimuths, all of 2003
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Locations vs predictions February 21-22, 2003
Location
030221, 12UT
030222, 00UT
030222, 12UT
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Jan 4-5 microbarom source at 0.135 Hz
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Microbaroms Concluding Remarks

• Microbaroms are generated wherever wave trains
  with opposite propagation directions interact.
  The strongest microbaroms may be generated in the
  wake regions of marine storms, where the
  amplitude of the opposing wave trains is
  greatest. In the two case studies, every
  propagating surface low exhibits a modeled wake
  region peak in source pressure. In the second
  case study observations from a network of
  infrasound stations show coherent microbaroms
  emanating from the wake regions of midlatitude
  cyclones.
• Microbaroms at I59US show an annual cycle
  associated with storm activity in the Pacific
  Basin. The majority of winter arrivals come from
  west and northwest directions, while summer
  arrivals come primarily from east and south
  azimuths. Arrivals during the shoulder seasons
  are move evenly distributed around the compass.
• Infrasound stations receive coherent arrivals
  from the strongest and closest source, therefore
  weaker signals will be masked, including those
  generated in wake of distant or weaker storms.
• New source model developed by UM. Possible
  application to passive acoustic tomography of the
  atmosphere.

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Sumatra Earthquakes 12/26/04 and 03/28/05
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Sumatra Tsunamis 12/26/04 and 03/28/05
12/26/04 Tsunami
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12/26 Diego Garcia, LF
Well defined azimuth sweep at low frequencies.
Palau under weather.
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12/26 Diego and Palau, HF
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03/28, Diego Garcia and Palau, LF
Palau
Palau
Small Tsunami! Very different at IS52
Diego
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Sumatra Concluding Remarks

• Submarine earthquakes can produce infrasound.
  The sound may be radiated by the vibration of the
  ocean surface or the vibration of land masses
  near the epicenter.
• The vibration of islands may produce infrasound.
• Infrasound stations can also serve as seismic
  and t-phase stations for large events.
• Small and large tsunamis may produce infrasound.
  The source process is not understood.
• There is a substantial difference between the
  information contained in the lower and upper
  frequency bands of the infrasound range.
• May be possible to use microbarom model.

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The End