The big map on the front page of today's New York Times is wrong on the travel times of the tsunami...by a lot. The map I linked to yesterday would be more likely to be correct. The link below is to equations for the velocity of shallow water waves-I used the approximation in eq. 2.9. Tsunamis are shallow water waves even in the deep ocean basins. I think that if somehow you got a short period tsunami that was not a shallow water wave, it would travel less fast than a long-period shallow water wave (someone can check that). The map in the New York Times shows that the tsunami would arrive at Mogadishu, Somalia in 6 hours. On page 17 of the .pdf document that I linked to yesterday are travel times from Pariaman, Indonesia, just 1/2 hour away from Dec 26 epicenter for a tsunami. This shows the travel time to Somalia at about 9 hours. Using the equation, and the distance from Dec 26 epicenter to Mogadishu of 5500+ km, and a water depth of 5000 m...velocity would be (sqrt(9.81 m/ss*5000m)=232 m/s*3600 s/hr=836 km/hr.
5500 km/836 km/hr=6.6 hrs. So, by this, it would sound like the New York Times would be closer. But, it is not...because 5000 m is the very deepest part of the Indian Ocean....you have to cross a spreading center at 2 to 3 km depth....and there are shallow plateaus and ridges. I'd guess from looking at our 1980 Atlas that the average depth along the path was less than 4 km..For 4000m, the velocity of a shallow water wave would be 713 km/hr...and the time would be 7.7 hours. For 3000 m average depth, 617 km/hr and 8.9 hours. Unless I am fouling up the equation, or I have the wrong equation, the New York Times is wrong. Of course, the best way to check this is to check the actual arrival time of the tsunami. Anyone?
Chris

• shallow wave equation