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GPS Requirements for Tsunami Detection
Y. Tony Song & Geoff Blewitt
Collaborators:Yoaz Bar-Sever, Yoaz Bar-Sever, Richard Gross, Vindell Hsu, Kenneth Richard Gross, Vindell Hsu, Kenneth Hudnut, Hans-Peter Plag ,Hudnut, Hans-Peter Plag ,Mark Simons, and Frank WebbMark Simons, and Frank Webb
Jet Propulsion Laboratory Jet Propulsion Laboratory NOAA (PTWC)NOAA (PTWC)USGS USGS Caltech Caltech University of Nevada RenoUniversity 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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Conclusion: Earthquake magnitude does not determine tsunami impact.
Date Location Magnitude Early Warning? Fatalities
26 Dec 2004 Sumatra 9.2 No Tsunami death~230,000
28 Mar 2005
19 July 2005
Nias Island
North California
8.7
7.7
Panic evacuation
False alarm
Evacuation killed ~100
No tsunami
27 Jan 2006
3 May 2006
19 July 2006
15 Nov 2006
Benda Sea
Tonga
South Java
Kuril Islands
7.6
8.0
7.7
8.3
?
False Alarm
No
False alarm/alert
No tsunami
No tsunami
Tsunami death~730
Small tsunami
13 Jan 2007
1 Apr 2007
15 Aug 2007
12 Sep 2007
Kuril Islands
Solomon Island
Central Peru
South Sumatra
8.1
8.0
8.0
8.4
False alarm/alert
No
Alert
Alert
No tsunami
Tsunami death~54
No tsunami
No tsunami
Recent Tsunami Events
11 events in 4 years
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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
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).
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).
Panic evacuation killed ~100 in March 2005
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Earthquakes Occur Near Coast
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GPS ApproachGPS ApproachSong, Y. T., Detecting tsunami genesis and Song, Y. T., Detecting tsunami genesis and
scales directly from coastal GPS scales directly from coastal GPS stations, stations, GRLGRL, , 3434, , doi:10.1029/2007GL03168 (2007).doi:10.1029/2007GL03168 (2007).
Tsunami TheoryTsunami TheorySong et al., Horizontal impulses of faulting continental Song et al., Horizontal impulses of faulting continental
slopes dictate tsunami genesis, slopes dictate tsunami genesis, Ocean Modell.Ocean Modell., , doi:10.1016/j.ocemod.2007.10.007 (2008)doi:10.1016/j.ocemod.2007.10.007 (2008)
Seismic inversion ApproachSeismic inversion ApproachSong et al., The 26 December 2004 tsunami Song et al., The 26 December 2004 tsunami
source estimated from satellite radar source estimated from satellite radar altimetry and seismic waves, altimetry and seismic waves, GRLGRL, , 3232, , doi:10.1029/2005GL023683 (2005).doi:10.1029/2005GL023683 (2005).
This talk is based on:
GPS ApproachGPS ApproachBlewitt, G., et al. Rapid determination of Blewitt, G., et al. Rapid determination of
earthquake magnitude using GPS for earthquake magnitude using GPS for tsunami warning systems. tsunami warning systems. GRLGRL, , 3333, , L11309, doi:10.1029/2006GL026145, L11309, doi:10.1029/2006GL026145, (2006)(2006).
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1. Tsunami Genesis
Tsunami TheoryTsunami Theory
Those earthquakes Those earthquakes transfer transfer oceanic energy 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 CaseLateral 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
Step 1: GPS displacements
Step 2: Seafloor displacement
Step 3: Tsunami energy
Calculating tsunami source energy from GPS displacements
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• 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
GPS 30-sec Series
Step1: GPS Displacements
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Step2: Seafloor Displacement
Seafloor motions derived from GPS data
rrNErU exp8
2exp)( 222
022exp)( errErE jj
022exp)( nrrNrN jj
GPS-inverted Seafloor Displacements
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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):
1. If ST < 5, local warning only.
2. If ST > 5, basin-wide warnings and modeling are needed.
3. Early warnings can be issued in few minutes after quake.
10log10 TT ES
Earthquake Magnitude Tsunami Energy(ET)
Tsunami Scale(ST)
Basin-wide Warning?
GPS GPS ST = 5 threshold
2004 Sumatra (Mw 9.2) 6.0e+15 J 5.8 >> 5 Yes
1964 Alaska (Mw 9.2) 8.2e+15 J 5.9 >> 5 Yes
2005 Nias (Mw 8.7) 2.8e+14 J 4.4 << 5 No
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Summary: Tsunami Prediction System
seafloor motions
Tsunami scales
GPS
3-D Ocean Model
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From Historical Tsunamis to GPS Requirements
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From Historical Tsunamis to GPS Requirements
1m
5 cm200 km 200 km
Tsunami height
GPS displacement
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NASA Decision Project: GPS-aided Real-Time Earthquake and Tsunami (GREAT) Alert System--Bar-Sever et al
Existing GDGPS (JPL/NASA)
Add into GDGPS
Coastal Real-Time GPS Network
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