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GPS Requirements for Tsunami Detection Y. Tony Song & Geoff Blewitt. Collaborators: Yoaz Bar-Sever, Richard Gross, Vindell Hsu, Kenneth Hudnut, Hans-Peter Plag , Mark Simons, and Frank Webb Jet Propulsion Laboratory NOAA (PTWC) USGS Caltech University of Nevada Reno. Tsunami Basics.

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Gps requirements for tsunami detection y tony song geoff blewitt l.jpg

GPS Requirements for Tsunami DetectionY. Tony Song & Geoff Blewitt

Collaborators:Yoaz Bar-Sever, Richard Gross, Vindell Hsu, Kenneth Hudnut, Hans-Peter Plag ,Mark Simons, and Frank Webb

Jet Propulsion Laboratory NOAA (PTWC)

USGS

Caltech

University of Nevada Reno


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Tsunami Basics

  • Tsunamis are usually caused by undersea earthquakes.

  • Tsunami waves travel at a speed of ~800 km/hour (or 200 m/s) in deep oceans.

  • A meter-height tsunami in the deep ocean can grow to tens of meters at coast.

  • Unlike wind-driven ocean waves that are only a disturbance of the sea surface, the tsunami wave energy extends to the ocean bottom.

2004 Indian Ocean Tsunami

Tsunamis occur after earthquakes


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Recent Tsunami Events

11 events in 4 years

Conclusion: Earthquake magnitude does not determine tsunami impact.


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The Consequence of Late Warnings

2004: tsunami death ~230,000

2006: tsunami death ~730

2007: tsunami death ~54


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The Consequence of False Alarms

Panic evacuation killed ~100 in March 2005

Since 1982, tsunami warnings based on earthquake magnitude have produced false alarms 16 out of 16 in Pacific (U.S. Government Accountability Office, GAO-06-519).

State of Hawaii’s estimation: an evacuation from a tsunami alarm would have cost the state $58.2 million in economic losses (Eddie Bernard, 1996).



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This talk is based on:

Tsunami Theory

Song et al., Horizontal impulses of faulting continental slopes dictate tsunami genesis, Ocean Modell., doi:10.1016/j.ocemod.2007.10.007 (2008)

Seismic inversion Approach

Song et al., The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves, GRL, 32, doi:10.1029/2005GL023683 (2005).

GPS Approach

Blewitt, G., et al. Rapid determination of earthquake magnitude using GPS for tsunami warning systems. GRL, 33, L11309, doi:10.1029/2006GL026145, (2006).

GPS Approach

Song, Y. T., Detecting tsunami genesis and scales directly from coastal GPS stations, GRL, 34, doi:10.1029/2007GL03168 (2007).


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1. Tsunami Genesis

Tsunami Theory

Those earthquakes transfer oceanic energy

Knowing how tsunamis are generated by earthquakes is the key to successful prediction.

Lateral motions of continental slopes are the main source of tsunami energy


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In the Sumatra Tsunami Case

  • Lateral motions of continental slopes are the main source of tsunami energy

  • potential energy = 1 (vertical)

  • kinetic energy = 5 (horizontal)


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2. Developing the GPS Method

Calculating tsunami source energy from GPS displacements

Step 1: GPS displacements

Step 2: Seafloor displacement

Step 3: Tsunami energy


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GPS 30-sec Series

Step1: GPS Displacements

  • Using estimated orbits

  • Rapid displacement

    • Data confirm that it arrives mostly with body waves

    • Can be resolved using 15-minutes after the quake

    • Accuracy ~ 7 mm

  • Can be used to estimate earthquake slip model

    • Model displacements ~ 3 mm

  • And keep in mind…

    • Network was far from optimal


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Step2: Seafloor Displacement

GPS-inverted Seafloor Displacements

Seafloor motionsderived from GPS data


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Step3: Determining Tsunami Scales

  • Earthquakes—Richter’s scale (magnitude)

  • Hurricanes—Simpson’s scale (category)

  • Tsunamis can be scaled (based on sqrt (ET) ~ tsunami height):

  • IfST < 5, local warning only.

  • If ST > 5, basin-wide warnings and modeling are needed.

  • Early warnings can be issued in few minutes after quake.


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Summary: Tsunami Prediction System

GPS

3-D Ocean Model

seafloor motions

Tsunami scales



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From Historical Tsunamis to GPS Requirements

Tsunami height

1m

5 cm

GPS displacement

200 km

200 km


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Coastal Real-Time GPS Network

NASA Decision Project: GPS-aided Real-Time Earthquake and Tsunami (GREAT) Alert System--Bar-Sever et al

Technical Requirements:

  • Network design (~10 km spacing)

  • Signal frequency (1 Hz)

  • Data accuracy (< 1 cm)

  • R/T GPS orbits and clocks (10 sec)

  • Data processing ( 2 min)

  • GPS-inversion seafloor displacement & tsunami energy estimation (2 min)

    Logistical Requirements:

  • International collaboration

  • Systems integration

Existing GDGPS (JPL/NASA)

Add into GDGPS


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