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

2 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 Indian Ocean Tsunami Tsunamis occur after earthquakes

3 Conclusion: Earthquake magnitude does not determine tsunami impact. DateLocationMagnitudeEarly Warning?Fatalities 26 Dec 2004Sumatra9.2NoTsunami death~230, Mar July 2005 Nias Island North California Panic evacuation False alarm Evacuation killed ~100 No tsunami 27 Jan May July Nov 2006 Benda Sea Tonga South Java Kuril Islands ? False Alarm No False alarm/alert No tsunami Tsunami death~730 Small tsunami 13 Jan Apr Aug Sep 2007 Kuril Islands Solomon Island Central Peru South Sumatra False alarm/alert No Alert No tsunami Tsunami death~54 No tsunami Recent Tsunami Events 11 events in 4 years

4 The Consequence of Late Warnings 2004: tsunami death ~230, : tsunami death ~ : tsunami death ~54

5 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 ). Panic evacuation killed ~100 in March 2005

6 Earthquakes Occur Near Coast

7 GPS Approach Song, Y. T., Detecting tsunami genesis and scales directly from coastal GPS stations, GRL, 34, doi: /2007GL03168 (2007). Tsunami Theory Song et al., Horizontal impulses of faulting continental slopes dictate tsunami genesis, Ocean Modell., doi: /j.ocemod (2008) Seismic inversion Approach Song et al., The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves, GRL, 32, doi: /2005GL (2005). This talk is based on: GPS Approach Blewitt, G., et al. Rapid determination of earthquake magnitude using GPS for tsunami warning systems. GRL, 33, L11309, doi: /2006GL026145, (2006) Blewitt, G., et al. Rapid determination of earthquake magnitude using GPS for tsunami warning systems. GRL, 33, L11309, doi: /2006GL026145, (2006).

8 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

9 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)

10 2. Developing the GPS Method Step 1:GPS displacements Step 2:Seafloor displacement Step 3:Tsunami energy Calculating tsunami source energy from GPS displacements

11 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

12 Step2: Seafloor Displacement Seafloor motions derived from GPS data GPS-inverted Seafloor Displacements

13 Step3: Determining Tsunami Scales Earthquakes—Richter’s scale (magnitude) Hurricanes—Simpson’s scale (category) Tsunamis can be scaled ( based on sqrt (E T ) ~ tsunami height ): 1.If S T < 5, local warning only. 2.If S T > 5, basin-wide warnings and modeling are needed. 3.Early warnings can be issued in few minutes after quake. Earthquake MagnitudeTsunami Energy (E T ) Tsunami Scale (S T ) Basin-wide Warning? GPS S T = 5 threshold 2004 Sumatra (M w 9.2)6.0e+15 J5.8>> 5 Yes 1964 Alaska (M w 9.2)8.2e+15 J5.9>> 5 Yes 2005 Nias (M w 8.7)2.8e+14 J4.4<< 5 No

14 Summary: Tsunami Prediction System seafloor motions Tsunami scales GPS 3-D Ocean Model

15 From Historical Tsunamis to GPS Requirements

16 From Historical Tsunamis to GPS Requirements 1m 5 cm 200 km Tsunami height GPS displacement

17 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