Making the map

Putting all this information together we can, for the first time, reconstruct the path and timing of the wave. This is what is shown in the map. Remember, you saw it first in Earth Talk in The National! It would be a bit boring to go through all the detail on which the map is based but here are some of the observations, just to show you how it was done. Firstly eyewitnesses at Arop and Malol told me that in fact they felt three earthquakes, the first being a very weak shake about ten minuites before EQ1. This also was noted by Colonel John Sanawe at Arop. Let's borrow some jargon from the seismologists and call this first event a foreshock. So survivors at Malol felt the foreshock, then EQ1, then EQ2. They said EQ2 was by far the strongest. The first wave arrived at Malol immediately after EQ2 had ceased shaking. If we say EQ2 shook for two minutes then the wave arrived at Malol at time EQ1 + 22 minutes. The wave was square on to the coastline. So we can draw a line parallel to the coast at Malol and label it with the number 22. Dickson Dalle, from his house on a hill above Aitape, observed that the wave approached Aitape from the northwest, rather than the north, so we can add a gentle curve to the end of the 22 line. Eyewitnesses on Tumileo Island felt two earthquakes that were equally strong, EQ1 and EQ2. The wave arrived on the west coast of Tumileo five minutes after EQ2 so we can draw a line between Aitape and Tumileo and label it with the number 27. Survivors from the "devastated" area between Arop and Nimas and westward to Sissano mission and airstrip felt only one earthquake. This suggests that the first wave arrived some time before the second earthquake, at perhaps EQ1 + 19 minutes or even as early as EQ1 + 18, or EQ1 + 17. At Arop, Warapu and Nimas the wave was square on to the shore, but at Sissano Mission it was oblique, sweeping along the coast from east to west. So we can draw a curved wave front and label it with the number 19. Yes it is a crude method, I agree, and involves some guesswork. But probably it is the best we can do. Surprisingly, the shape of the wave front is quite similar to that shown in The Wave video tape. Perhaps Father Mlak had inside information! Two more conclusions can be drawn from this map. First, we can estimate the speed of the wave by measuring the distances between the three wave front lines and dividing by the elapsed time. The result is around 16 metres per second, which is not too far off the speed of 10 to 15 metres per second that was estimated by the international team, using other evidence. The second is that from the shape of the wave front we can locate, roughly, the point that the tsunami started from. My guess is that this point was 20 km straight out to sea from the Otto mouth. What do you think?