General-Circulation- Model System for Global Tsunami Warning

Transcription

1 A Coupled Teleseismic Ocean-General General-Circulation- Model System for Global Tsunami Warning Y. Tony Song Jet Propulsion Laboratory, California Institute of Technology Contents:. Tsunami formation theory 2. Methodology of seismic prediction Dec 24 & 28 Mar 25 Tsunamis 4. Summary Contributors: L.-L. Fu & Victor Zlotnicki (NASA JPL) Chen Ji & Vala Hjorleifsdottir (SeismoLab, Caltech) C.K. Shum & Y. Yi (Ohio State University)

2 Facts: Too Many False Alarms A strong earthquake does not necessarily results in a proportionally strong tsunami. July 998 New Guinea M7.5; 5m run-up up and 2, fatalities March 25 N. Sumatra M8.7; 2m run-up up and fatalities, due to evacuation June 25 Northern California M7.; triggered a tsunami alert; no tsunami Without knowing how tsunamis form from earthquakes,, it would be impossible to predict a tsunami precisely. For a long time, it has been believed that the under earthquakes that involve a significant vertical motion are more effective in generating tsunamis than those that primarily horizontal motion (Pond & Pichard 983; Satake 995). The old theory is wrong!

3 Earthquake Fault & Topography 5N 2 km (a) Topography km N 2 Vertical motions 5N 3 km 4 km Eq 9E 92E 94E 96E 98E 3 4 (b) Section 5 o N Lateral motion Depth (km) Slip 5 92E 93E 94E 95E 96E Longitude Mega tsunamis are caused by horizontal motions of continental slopes!

4 TOPEX/Poseidon Tude gauges Sea Surface Height Data used in this study P b h = ζ gρdz Ocean Ocean Bottom Pressure () The Global Seismographic Network gives the seismic waves generated by the undersea earthquake. (2) Satellite radar altimeters measure the sea-surface surface waves tsunami, caused by the seafloor motions (3) Tide gauges record shallow waves or run-up up to beaches

5 Method : Seismic Waveform Inversion u( t) n n = j= k= D 2 [ cos( λ ) Y ( V, t) + sin( λ ) Y ( V, t) ] S ( t) Dynamical seafloor deformation 4N (a) Displacement 4N (b) Topography 2N 2N N N 8N 8N 6N 6N 4N 4N 2N 2 m 2N GPS measurements from C. Vigny (Nature 25) Fault area survey by British Navy (K. Moran) 9E 92E 94E 96E 98E meter 2 2 9E 92E 94E 96E 98E km

6 Method 2: Deriving tsunami source energy Seismic data inverted 3D seafloor motions: (u, n, e) upward, northward and eastward fault displacement Vertical uplift: η = at sea-surface u + eh x + nh y Horizontal displacement: ( u, v ) = ( δ ( z) e, δ ( z) n) b b within the bottom layer of z < L H hx x y Tsunami potential energy: PE=5.4 x 4 Joule Amp=3% Tsunami kinetic energy: KE=2. x 5 Joule Amp=7%

7 Method 3: Ocean Models with Bottom-Layer Forcing. S-coordinate (Song&Haidvogel 994): z = ζ ( + s) + h s + ( H h ) C( s) c c SCRUM/ ROMS (Boussinesq) 2. Sp-coordinate (Song&Hou 25): p = p s ( + s) ( p ' b + p c ) s ( p b p c ) C( s) Ocean-bottom-pressure model (non-boussinesq) Three-dimensional seafloor motions are applied

8 Prediction system: Seismograph to Tsunami Waves u( t) n n = j= k= D 2 [ cos( λ ) Y ( V, t) + sin( λ ) Y ( V, t) ] S ( t) 2 Bottompressure coupling 3

9 N N (a) 2: hrs after quake Validations by Satellites and Tide-Gauges 3N (b) 3: hrs after quake 2N N N Eq Eq S Jason 2S 7E 8E 9E E E S Envisat 2S 7E 8E 9E E E 8 (c) Jason track Jason data Model: 6 S 5S Eq 5N N 5N 2N 2S S Eq. N 2N Asymmetric N-Waves Leading depression waves toward Thailand Leading elevation waves toward Sri Lanka SSH (cm) (d) Envisat track Envisat data Model: propagating westward propagating eastward Belawan Sibolga Male Gan Hanima (a) Vertical only Data 2 m Model Receding first Elevating first (b) Vertical & Horizontal Belawan Data Model Sibolga Male Gan Hanima Dec Dec Tony Song, January 26

10 4N 3N 2N N T=3 sec m/s Seismic Prediction of 28 March 25 a) Horizontal slip EQ 95E 97E 99E km N 3N 2N N T=3 sec b) Vertical uplift (cm) EQ 95E 97E 99E N 5N 5N 5S c) 28 Mar tsunami (slip & uplift) * Male 5S 7E 8E 9E E Residual (cm) Dec4 28 Mar5 d) Tide at Male Data Model 2h 4h 6h 8h The horizontal slip has occurred in the shallow and relatively flat region; therefore, it is ineffective for generating long waves.

11 Conclusion Remarks Evidence from seismometers, satellite altimeters, and tide gauges s suggests that horizontal motions of faulting are the main cause of the Indian Ocean tsunami. The vertical uplift accounts for only 3% of the tsunami i height. Implications:. Movement of continental margins,, rather than the local vertical uplift of seafloor,, should be the focus of tsunami observation and prediction. 2. Many remote-sensing technologies (e.g., GPS), combining with the proposed methodology, become useful for tsunami detection. 3. Seismic prediction of tsunamis is feasible: Based on JPL s s supercomputer, the coupled earthquake-tsunami tsunami modeling system is going to connect to the global-seismographic seismographic-network. Song et al., GRL, 32,, doi:.29/25gl23683 (25). Song et al., Horizontal motions of faulting dictate the 26 December tsunami (submitted to Nature).