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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