Thursday, March 31, 2011

Tsunami: How Long it Took for the Crest to Arrive


BBC has the details on the town in which this video was shot ... it was one of few which survived because it had an unusually high sea wall. Read the details.

2 comments:

Dave in Pa said...

How high should those sea walls be?

The scientific consensus is that this earthquake was a 9.0 on the Richter scale. The Richter scale is logarithmic, that's to say a 9.0 is 10X times as strong as an 8.0 is 10X as strong as a 7.0, etc. For historical comparison, the scientific consensus on the Great 1906 Earthquake that destroyed San Francisco and much of the Bay Area was that it was an 8.0.

Given Japan's being on the edge of the "Pacific Ring of Fire", logic suggests that most if not all of the country's coast have substantial sea walls. A 9.0 may be a "once every few centuries" earthquake but sea walls to contain at least an 8.0 earthquake-caused tsunami would seem not unreasonable. Not even considerign the tens of thousands of dead, but looking at it from a cost accounting perspective, that would be an extremely expensive national project. However, that's far less than the cost of fixing most of the northern half of Honshu island will be after this disaster. The latest rough estimate I read was a quarter trillion dollars...and counting.

AND LET'S NOT FORGET: the western coasts of Canada and the US are sitting on the eastern edge of the "Pacific Ring of Fire". It's not a question of if but when either or both countries get hit by another huge earthquake.

Tom Riel said...

There are 2 other facts to consider - this earthquake was the strongest ever recorded in Japan, and from an area not expected until very recently to have the potential of such a strong quake, and the quake itself caused a 3 ft. subsidence in the land immediately after the quake so that a 30 ft. sea wall suddenly became a 27 ft sea wall.