How big was the tsunami from the recent Japan earthquake?

[StevieTNZ]

Quite recent, so updates will follow. Over the radio in NZ, it is said a tsunami warning has been issued.

Magnitude 7.3 at the moment, possibly be revised.

http://www.stuff.co.nz/world/asia/86723022/big-earthquake-near-japan

 

[fresh_42]

... half a dozen news channels in three languages and all they got is a news ticker line ...

 

[CapnGranite]

A tsunami advisory was issued for Fukushima, but the Pacific Tsunami Warning center has, at this point, not issued any alerts for the west coast of North America or Alaska

 

[davenn]

large P wave on my seismo

http://www.sydneystormcity.com/seismograms.htm

USGS showing M 6.9 at the moment

 

[StevieTNZ]

A tsunami advisory was issued for Fukushima, but the Pacific Tsunami Warning center has, at this point, not issues any alerts for the west coast of North America or Alaska

With us:

Possible tsunami threat to NZ after magnitude 7.3 quake strikes near Japan.

 

[fresh_42]

correction: 12 news channels in 4 languages and out of all the Japanese channel is the only one broadcasting it ...
Does the 20 km refer to depth or "off the coast line" - I can't read Japanese - they all report 7.3

NHK: Tsunami (JP) underway, already observed

 

[davenn]

Does the 20 km refer to depth

most likely

 

[fresh_42]

They expect 3 m. (observation 9 min ago: 60 cm on sea)

 

[davenn]

must be reasonably deep, very little surface waves

 

[fresh_42]

most likely

Meanwhile I think it's both, since on one chart they had it twice.

 

[fresh_42]

The best part is that one can watch it guilt-free, for the Japanese can certainly deal with 3 m.

 

[davenn]

Meanwhile I think it's both, since on one chart they had it twice.

a google Earth on the epicentre puts it at about 33km offshr , it's going to be give or take a bit

 

[StevieTNZ]

Now at 6.9.
"A tsunami, predicted to reach as much as 3 metres, has been observed. Residents are urged to flee.

There is no tsunami threat to New Zealand as a result."

Live updates roll in on this site -- http://www.stuff.co.nz/world/86724428/live-japan-73-quake

 

[fresh_42]

Local broadcast is still at M7.3. Observed heights until now between 30 cm and 90 cm.
... and of course the usual say from officials like Tesco: There will be no threads to the population at any time and all is under control.
(... although they've said something like the cooling system has stopped operating not without to mention that the water tanks are full.)

 

[davenn]

Local broadcast is still at M7.3.

the media always take a long time to get things right

Now at 6.9.

see post 4 an hour ago ;)D

 

[fresh_42]

the media always take a long time to get things right

... plus a 7+x sells better than a 6+x.

 

[davenn]

hahaha uh huh

 

[fresh_42]

hahaha uh huh

By the way: they have corrected their notation now!

Spoiler

M7.4!

At least they have their cooling system running again. Max height experienced: 1.4 m.

 

[davenn]

interesting .. the USGS are still sitting on 6.9
wouldn't be the first time I have seen them under rate a quake

 

[fresh_42]

interesting .. the USGS are still sitting on 6.9
wouldn't be the first time I have seen them under rate a quake

What I don't understand about it is, that the Richter-scale is based on local (in a radius of a few 100 km) measurements (at least what's written on Wiki), so shouldn't the Japanese measurements be more accurate? The more they certainly have enough experiences. I would expect an eventual difference of about $\pm 0.15$ due to uncertainties of measurements. On the other hand the recent NZ quake which has been more difficult to measure resulted in equal reports around the globe. Btw. the GFZ in Potsdam has 6.9 (http://geofon.gfz-potsdam.de/eqinfo/seismon/globmon.php)

 

[davenn]

What I don't understand about it is, that the Richter-scale is based on local (in a radius of a few 100 km) measurements (at least what's written on Wiki), so shouldn't the Japanese measurements be more accurate? The more they certainly have enough experiences. I would expect an eventual difference of about $\pm 0.15$ due to uncertainties of measurements. On the other hand the recent NZ quake which has been more difficult to measure resulted in equal reports around the globe. Btw. the GFZ in Potsdam has 6.9 (http://geofon.gfz-potsdam.de/eqinfo/seismon/globmon.php)

The Richer Scale is rarely used these days ... pretty much the only ones you hear using it are the media

As I said earlier ...

the media always take a long time to get things right

all the local sensors would have maxed out on an even of this size, so difficult to get an accurate reading to lots of data from more distant sensors is analysed

Mw = moment magnitude is the standard one used in recent years
It gives a good true description of the size of the event

Based on the scalar seismic-moment of the earthquake, as determined by a moment-tensor inversion. Mwb – Mw based on moment tensor inversion of long-period (~10 - 100 s) body-waves (P- and SH). Mwc -- Moment magnitude derived from a centroid moment tensor inversion of intermediate- and long-period body- and surface-waves. Mwr -- Moment magnitude derived from a moment tensor inversion of complete waveforms at regional distances (less than ~13 degrees). Sometimes called RMT. Mww -- Moment magnitude derived from a centroid moment tensor inversion of the W-phase.

have a look here for all the different magnitude scales and what limitations/advantages they have

http://earthquake.usgs.gov/data/comcat/data-eventterms.php#magType

Note Richter magnitude is the second one down the list ... Local magnitude = MLDave

 

[russ_watters]

So I'm guessing the tsunami didn't amount to anything? It seems to have fallen off the news...

 

[StevieTNZ]

So I'm guessing the tsunami didn't amount to anything? It seems to have fallen off the news...

No damaging tsunami's, but did happen.

 

[davenn]

So I'm guessing the tsunami didn't amount to anything? It seems to have fallen off the news...

around 1.5 - 2 metres