Re: 60th Anniversary of 1946 April Fool's Day Quake & Tsunami

On 2006-03-23 15:19:26 -1000, David Oberman <doberman@xxxxxxxxxxxxxxxxxx> said:

Gerard Fryer <gerard@xxxxxxxxxxxxxxxxx> wrote:

The first of the aftershocks was more impulsive than the main shock, so it felt as strong though it did not last as long.

Because the Aleutian Shelf is so shallow (about 100m) and broad (100km), the tsunami had to begin within a minute of the main shock. Either it was excited directly by the earthquake or the landslide started moving right away. Scotch Cap Light was destroyed 48 minutes after the main shock, and the tsunami travel time from the shelf edge to the lightyhouse is 43 minutes. The aftershock was some minutes later, leaving too little time for a tsunami from the aftershock to reach its destination.

Thanks, Gerard!

is it known whether the first crest was the biggest? There's something
about this particular event that is very fascinating.

The first crest was definitely not the biggest. The same thing was noted all around the Pacific: the first couple of waves were fairly small; it was the later waves that were the doozies. In Hawaii, the first deaths did not occur until wave number 3, half an hour after the phenomenon had started. If people had just understood what they were seeing and walked away from the ocean, there would have been no deaths.

Ironically, in the Marquesas, the only deaths involved someone who very much understood what she was seeing. A young woman at Tahauku on Hiva Oa raised the alarm after the first wave, and went from house to house to make sure people understood. Then she went to her own house to get her baby. She and her baby were the only casualities.

The emergent nature of the 1946 tsunami has been a challenge to tsunami modelers trying to make an earthquake source fit. Yuichiro Tanioka has come closest, by invoking sediment deformation at the shallow end of the fault (i.e., by making the earthquake look like a landslide :-)

--Gerard

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