1. Improving Estimates of Tsunami Propagation Speed
Victor C. Tsai
Seismological Laboratory
Division of Geological and Planetary Sciences
California Institute of Technology
Institute for Earth Science, Academia Sinica
March 19th, 2014

2. March 11, 2011; Tohoku, Japan

3. Modeled Tsunami Amplitude
Courtesy of NOAA

4. Understanding Tsunami Propagation
Tsunami speed given by
Numerical models based on this assumption work reasonably well

5. Taking a Step Back How fast do tsunamis travel? Simple to understand?
Improving the model?
Philosophy:
The simpler it is to understand the derivation, the easier it is to make improvements to the model

6. How fast does a tsunami travel?
Simple theory to understand this
Analogy to mass on spring ,
frequency:
speed: M K

7. How fast does a tsunami travel?
Simple theory to understand this
Analogy to mass on spring ,
frequency:
speed: M K

8. Waveform Comparison Observed (black) Synthetic (red) based on
~17 hrs
After 17 hrs, synthetics are early by ~15 mins!
Lay et al., 2011

9. Tsunami Speed Discrepancy (in percent)
Timing discrepancy is wavelength dependent
WHY is there a discrepancy???
Watada et al., 2011

10. Why?

11. Why? Ocean currents? Ocean bottom friction? Incorrect bathymetry?
Coriolis effects?
Local g variability?
Solid Earth deformation?
Density differences?

12. The Two Biggest Differences
Solid Earth deformation under the ocean is important
Density differences within the ocean are important

13. The Two Biggest Differences
Solid Earth deformation under the ocean is important
Why? Total Earth elastic displacement is significant
Density differences within the ocean are important
Why? Compressibility is significant

14. A More Detailed Calculation
Solid Earth deformation under the ocean is important
Energy calculation: , 

15. A More Detailed Calculation
Density differences within the ocean are important
Similar type of energy calculation … , 

16. Tsunami Speed Discrepancy (in percent)
Timing discrepancy is wavelength dependent
WHY is there a discrepancy???
Including solid
Earth deformation
+ density also
Accounts for ~60-90% of discrepancy
Tsai, Ampuero, Kanamori, & Stevenson, GRL 2013

17. Conclusions Questions? Tsunami propagation is easily understood
Errors from other effects easily estimated
New model including solid Earth deformation and ocean density differences explains anomalies
Simple models and estimates are useful
Questions?