Previous Tohoku Earthquakes

[Mulboyne]

National Geographic: The Recent Earthquake Wave on the Coast of Japan (1896)

Video of 1933 Quake

(Also a 1964 clip of the Niigata quake here)

[Bucky]

[dimwit]

From the National Geographic story:


. . . you would think with this sort of history that seawalls or breakwaters would have been specced much higher than what they are. I seem to recall the Fukushima seawall as being a max of 20 feet tall. Doh!:wall:

Or given the frequency of earthquake-induced tsunamis not build nucleur reactors anywhere on the Pacific coast side of Japan.

Seawalls probably give people in the affected communities an extra minute at most to flee the tsunami. Were they to have been higher they would have cost much more than the value of the property they were protecting. The biggest problem with them is that they gave far to many people a false sense of security, in building residental areas far to close to the sea on lowlaying land. Worse still causing many to not immediately flee to higher ground on the assumption that the seawall would hold the water back.

[matsuki]

Or given the frequency of earthquake-induced tsunamis not build nucleur reactors anywhere on the Pacific coast side of Japan.

Seawalls probably give people in the affected communities an extra minute at most to flee the tsunami. Were they to have been higher they would have cost much more than the value of the property they were protecting. The biggest problem with them is that they gave far to many people a false sense of security, in building residental areas far to close to the sea on lowlaying land. Worse still causing many to not immediately flee to higher ground on the assumption that the seawall would hold the water back.

Should be more accurately named tsunami speed bump....calling it a wall, regardless of height, seems to make people feel safe....well, it used to.

[Mulboyne]

What struck me, reading about the 1896 tsunami, is that the waves may have reached heights of up to 100ft even though the quake itself didn't seem to be of a magnitude to produce that reaction.

It appears that there is a type of earthquake called a "tsunami earthquake" where this discrepancy is very pronounced. TEPCO's planning didn't seem to consider this possibility and you wonder which other parts of the country are also ignoring that risk.

[dimwit]

What struck me, reading about the 1896 tsunami, is that the waves may have reached heights of up to 100ft even though the quake itself didn't seem to be of a magnitude to produce that reaction.

It appears that there is a type of earthquake called a "tsunami earthquake" where this discrepancy is very pronounced. TEPCO's planning didn't seem to consider this possibility and you wonder which other parts of the country are also ignoring that risk.

The worst tsunamis are not necessarily produced by the largest magnitude earthquakes. What may have happened in 1896 was that the quake produced a submarine avalanche where a large chunk of the continental shelf broke off. In that case, the displacement of water can be truely immense. A magnitude 7 earthquake can produce a tsunami in that way which is the reason that they have tsunami warnings after many quakes in which the fault displacement would not seem to be very large.