GPS Requirements for Tsunami Detection Y. Tony Song

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GPS Requirements for Tsunami DetectionY. Tony
Song Geoff Blewitt
CollaboratorsYoaz Bar-Sever, Richard Gross,
Vindell Hsu, Kenneth Hudnut, Hans-Peter Plag
,Mark Simons, and Frank Webb Jet Propulsion
Laboratory NOAA (PTWC) USGS Caltech Universi
ty 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 Hawaiis 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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Earthquakes Occur Near Coast
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This talk is based on
Tsunami Theory Song et al., Horizontal impulses o
f faulting continental slopes dictate tsunami
genesis, Ocean Modell., doi10.1016/j.ocemod.2007.
10.007 (2008)
Seismic inversion Approach Song et al., The 26 De
cember 2004 tsunami source estimated from
satellite radar altimetry and seismic waves, GRL,
32, doi10.1029/2005GL023683 (2005).
GPS Approach Blewitt, G., et al. Rapid determinat
ion of earthquake magnitude using GPS for tsunami
warning systems. GRL, 33, L11309,
doi10.1029/2006GL026145, (2006).
GPS Approach Song, Y. T., Detecting tsunami genes
is and scales directly from coastal GPS stations,
GRL, 34, doi10.1029/2007GL03168 (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 di
splacement
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 motions derived from GPS data
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Step3 Determining Tsunami Scales

• EarthquakesRichters scale (magnitude)
• HurricanesSimpsons scale (category)
• Tsunamis can be scaled (based on sqrt (ET)
  tsunami height)

• If ST
• 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
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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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NASA Decision Project GPS-aided Real-Time
Earthquake and Tsunami (GREAT) Alert
System--Bar-Sever et al
Coastal Real-Time GPS Network

• Technical Requirements
• Network design (10 km spacing)
• Signal frequency (1 Hz)
• Data accuracy (
• 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