From AP via chicoer.com
TOKYO — Japan was rattled by a strong aftershock and tsunami warning Thursday night nearly a month after a devastating earthquake and tsunami flattened the northeastern coast.
The Japan meteorological agency issued a tsunami warning for a wave of up to 6 feet. The warning was issued for a coastal area already torn apart by last month’s tsunami, which is believed to have killed some 25,000 people and has sparked an ongoing crisis at a nuclear power plant.
Officials say Thursday’s aftershock was a 7.4-magnitude and hit 25 km under the water and off the coast of Miyagi prefecture. The quake that preceded last month’s tsunami was a 9.0-magnitude.
Buildings as far away as Tokyo shook for about a minute.
full story here
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http://ptwc.weather.gov/ptwc/text.php?id=pacific.2011.04.07.143955
TSUNAMI BULLETIN NUMBER 001 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 1439Z 07 APR 2011 THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA... WASHINGTON...OREGON AND CALIFORNIA. ... TSUNAMI INFORMATION BULLETIN ... THIS BULLETIN IS FOR INFORMATION ONLY. THIS BULLETIN IS ISSUED AS ADVICE TO GOVERNMENT AGENCIES. ONLY NATIONAL AND LOCAL GOVERNMENT AGENCIES HAVE THE AUTHORITY TO MAKE DECISIONS REGARDING THE OFFICIAL STATE OF ALERT IN THEIR AREA AND ANY ACTIONS TO BE TAKEN IN RESPONSE. AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS REPORTED BY THE JAPAN METEOROLOGICAL AGENCY. ORIGIN TIME - 1432Z 07 APR 2011 COORDINATES - 38.2 NORTH 142.0 EAST DEPTH - 40 KM LOCATION - NEAR EAST COAST OF HONSHU JAPAN MAGNITUDE - 7.4 EVALUATION NO DESTRUCTIVE WIDESPREAD TSUNAMI THREAT EXISTS BASED ON HISTORICAL EARTHQUAKE AND TSUNAMI DATA. HOWEVER - EARTHQUAKES OF THIS SIZE SOMETIMES GENERATE LOCAL TSUNAMIS THAT CAN BE DESTRUCTIVE ALONG COASTS LOCATED WITHIN A HUNDRED KILOMETERS OF THE EARTHQUAKE EPICENTER. AUTHORITIES IN THE REGION OF THE EPICENTER SHOULD BE AWARE OF THIS POSSIBILITY AND TAKE APPROPRIATE ACTION. THIS WILL BE THE ONLY BULLETIN ISSUED FOR THIS EVENT UNLESS ADDITIONAL INFORMATION BECOMES AVAILABLE. THE JAPAN METEOROLOGICAL AGENCY MAY ALSO ISSUE TSUNAMI MESSAGES FOR THIS EVENT TO COUNTRIES IN THE NORTHWEST PACIFIC AND SOUTH CHINA SEA REGION. IN CASE OF CONFLICTING INFORMATION... THE MORE CONSERVATIVE INFORMATION SHOULD BE USED FOR SAFETY. THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA. =================================================================Earthquake Details
- This event has been reviewed by a seismologist.
| Magnitude | 7.1 |
|---|---|
| Date-Time |
|
| Location | 38.253°N, 141.640°E |
| Depth | 49 km (30.4 miles) |
| Region | NEAR THE EAST COAST OF HONSHU, JAPAN |
| Distances | 66 km (41 miles) E of Sendai, Honshu, Japan 114 km (70 miles) E of Yamagata, Honshu, Japan 116 km (72 miles) ENE of Fukushima, Honshu, Japan 330 km (205 miles) NNE of TOKYO, Japan |
| Location Uncertainty | horizontal +/- 13.1 km (8.1 miles); depth +/- 7.2 km (4.5 miles) |
| Parameters | NST=426, Nph=427, Dmin=358.4 km, Rmss=0.75 sec, Gp= 32°, M-type=regional moment magnitude (Mw), Version=B |
| Source |
|
| Event ID | usc0002ksa |
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those poor people, already so bad and possibly more harm.
and a tsunami possibly taking more of the soil etc into the sea wouldnt be good.
For those of you with Google Earth, the epicenter has been marked up by Google. It’s a lot closer to shore than the original, and can only be called an aftershock at magnitude 7.1 by comparison to the much larger 8.9 magnitude monster EQ.
A 2 meter tsunami shouldn’t overtop the tsunami walls.
Someone, somewhere has mistranslated something. Nowhere on earth is there water 25 miles deep.
I thought my house was going to shake apart. (I’m in east Koriyama city, Fukushima, and house is 54km due west from the Fukushima Dai-ichi nuclear power plant).
0113hrs as I type this and waiting for my nerves to calm down.
Regards
Kevin.
Current situation at 0116hrs JST : No tsumani observed as of yet however a minor change in sea level detected in one area, and no tsunami disaster expected. Tsunami warnings lifted.
No further damage or further anomalies in the Fukushima nuclear reactors.
Onagawa nuclear power plant in Miyagi has lost 2 out of 3 external power transmission lines supplying it, after it was shut down safely after the 11th March quake.
More intense aftershocks are to be expected.
Power outages across all of Aomori, Iwate, Akita; also parts of Miyagi, Yamagata
My own lights flickered lots about 10 seconds before the seismic waves hit my house.
Power still operating in Koriyama city.
My nerves are still quaking.
Regards
Kevin.
good Lord…those poor people
NHK World has excellent coverage in English at : http://www3.nhk.or.jp/daily/english/
Regards
Kevin.
0134hrs JST
Monitoring stations at Fukushima 1&2, Onagawa nuclear power stations show no change following the aftershock, according to the cabinet office.
Those poor people just can’t catch a break, can they?
This is worrying of course but I’m confused by the use of the word ‘depth’. Does it actually mean ‘distance from land’?
Thank you very much for your updates, Kevin.
Cool observations under pressure – or under shakings, external and internal – are extremely valuable, and tell more than a press notice.
I hope you, your friends and family are ok.
Jay Davis says:
April 7, 2011 at 9:13 am
No, you misunderstand. It means 25 miles under the seabed.
DaveE.
Jay Davis says:
Someone, somewhere has mistranslated something. Nowhere on earth is there water 25 miles deep.
Not sure but I think it means depth in the crust, not depth in the ocean. Although that’s still pretty deep.
“Depth” in this case means the actual location — the focus, or hypocenter — of the quake. They’re saying the actual break in the rock occurred 25 miles down. The “epicenter” is the point on the Earth’s surface directly above the focus.
What was up with the blue light?
“Depth” is how far down in the earth the tectonic rupture occurred, i.e. Where the actual slipping of rock against rock happened. Latitude, longitude, and depth define the 3d location of the quake which is called the “hypocenter”. The “epicenter” is the projection of that 3d point vertically to the surface — the point directly above the hypocenter.
Some of you may remember one or two of my posts in the previous earthquake thread, when I started a daily updates of quakes and geomagnetic activity, prompted by the New Zealand’s earthquake.
Data isn’t yet sufficiently numerous to have any pronouncements.
http://www.vukcevic.talktalk.net/EQr.htm
Updates are at 8am UTC (results plotted refer to the previous 24h)
Which is probably why the quote is “25 km under the water” and not under water.
Suspect that ‘depth’ is the depth of the epicentre of the quake in the Earth’s crust.
Depth of 25 km.
Clearly, it cannot be the depth of water. I strongly suspect this is referring to the depth in the solid earth i.e. the depth starting at the sea bed and going down.
Earthquakes are common at subduction zones well below the ocean bottom. The subsiding plate “sticks” for a while, stress builds up and something gives to produce the earthquake.
I believe the ‘depth’ is referring to the depth in the earth where the epicenter was. Not unusual for it to be many miles below the surface of the earth.
Since it’s quiet and all those people who know better than me aren’t putting it out there, the use of ‘depth’ seems quite correct.
http://en.wikipedia.org/wiki/Earthquake
“The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers. Earthquakes occurring at a depth of less than 70 km are classified as ‘shallow-focus’ earthquakes, while those with a focal-depth between 70 and 300 km are commonly termed ‘mid-focus’ or ‘intermediate-depth’ earthquakes.”
Bolds are my own. I admit it’s only my guess that all earthquake depths are measured from sea-level whether quakes occur under the ocean or beneath exposed land but it would be interesting to know for sure if anyone could confirm or correct me on that.
Further to the above question, would I be right in guessing that these depths are determind by following back the various measurements of the shockwaves to their starting point using Time Delays?
Duncan B, it happened in the rock beneath the ocean. That 49 km depth is probably below sea surface level. the word Depth is a link to a glossary – that is quite busy right now. — John M Reynolds
I believe depth is below the surface of the earth.
25 miles is pretty deep, a shallow quake would be a few miles or less.
(BIANAS) But I am not a seismologist!
Kevin Cave, thanks so much for the updates!
Are you close enough to the coast (54 km) to be directly affected by the shelters? I would think anyone with relatives or friends would move there first if possible. I’ve been following this every few hours since the big one hit.