7.8 Quake Just hit Japan- southern islands- Reduced from 8.5

a reply to: jimmyx

Now that quake in California has been pulled from the USGS map altogether.

a reply to: liteonit6969

ATS has its very own earthquake watchers, who, umm, shall we say... are like on top of things...

originally posted by: AshOnMyTomatoes
a reply to: jimmyx

Now that quake in California has been pulled from the USGS map altogether.

Yep. Was probably a false trigger from the 7.8...

With the closest station I know of some 600 km away or so, another problem with this quake will be monitoring aftershocks. 4.0's and less may not even show up anywhere. But I am finally seeing a small one, so that, in a sense is good. Hopefully this will follow a typical mainshock-aftershock sequence and will not be a foreshock.


ETA: there are three buoys in event mode surrounding that epicenter:

www.ndbc.noaa.gov...

a reply to: hopenotfeariswhatweneed

Far out another massive quake.....is it just my imagination or are there an above average amount of large quakes in the recent past ?

With the increase in earthquakes, sink holes, mass animal deaths, increase in weather related storms, terrorism around the world, the threat of war, losing some of our constitutional rights, and police are becoming increasing militant, it definitely seems like we're going through some turbulent and changing times.

a reply to: AshOnMyTomatoes
That's not a rare situation. As TA said, it was probably a false trigger from the big quake off Japan.

I saw the same thing a day or so ago right after the 6.8 Mw (downgraded to 6.7) in the Alaskan island chain. A couple of red dots popped up in Nth cal and one was about a 5.1, if I recall correctly. The other was smaller. Then a few minutes later, after seismologists had had a chance to manually review the data, they were pulled. I couldn't find any reports from local residents in the area of a quake, so they were just false triggers.

@ TA: with this quake being so deep, it seems less likely to me that it may be a foreshock for a larger event nearer the surface within the "usual" megathrust/subduction zone quake range of depths. For example, the mag 7.3 Mw foreshock (on March 9) before the main Tōhoku quake of March 11, 2011 was only 32km deep, versus the main shock's 29 km. I can't recall a great quake with a foreshock at several hundred km deep. However, I'd appreciate your opinion on it.

a reply to: JustMike

Well, I was just checking up on the slab profile for the Izu trench, and here is a pic:
earthquake.usgs.gov...

It appears this quake does fit the depth profile closer than I originally thought. Been a while since I'd looked at it. So all in all I'd say chances are probably not a foreshock. Just a deep, big quake. They happen from time to time. But in and around Japan, never, EVER let down the guard. If March 11 (the 9.0) taught us nothing else, it was that.

ww2.volcanodiscovery.com...

Hi TA,

In your opinion, could this volcano have anything to do with this earthquake?

And are you thinking pre-curser to something bigger?

Thanks for your reply.

a reply to: crappiekat

Hi ck,
Imo, probably not. It is much too deep and much too far from that volcano, and/or any other volcanoes in Japan for that matter. But that's just my opinion.

originally posted by: TrueAmerican
a reply to: liteonit6969

ATS has its very own earthquake watchers, who, umm, shall we say... are like on top of things...

Indeed and I thank you all for it. Better coverage here almost always.

Scary stuffstuff though at those high numbers.

a reply to: TrueAmerican

Hello,
Is there anyway I can make the map bigger ie fullscreen, am not so familiar with those things to do that...



Thanks,

a reply to: TrueAmerican

Geez....how does it get down-graded THAT much?

Also am now simply more amazed/stunned that Cali hasn't had a big one lately. I mean the entire
Pacific rim is ringing with quakes and volcanoes. It's perplexing.

a reply to: kosmicjack

Well, if you are an emergency services provider such as the PTWC and/or USGS, and you are dealing with a quake that big, and are not sure because of all the other reasons I have mentioned here- then it is best to overestimate. Get the people's attention, and prepare for the worst while hoping for the best. Until data is thoroughly analyzed, from multiple sources, one cannot be sure of just how big a quake is when every station all over the world starts lighting up with seismic waves. And when the closest station is like 600 km away, you can't get a good immediate read on it. And for those of us who regularly watch seismic data, magnitude reductions of 1 full mag are not unheard of. So a .7 reduction considering the circumstances is not that bad. Lives in Hawaii or Guam could be lost if a tsunami came slamming in unexpectedly.

The point is, I can understand their position and the problems associated with a big quake in this unmonitored spot. Better safe than sorry.

What makes an Earthquake at sea , cause a tsunami. I mean the times.when tsunamis appear from sea quakes does that have to do with depth or slides or something else? Just wondering about that...

Wow, this is creepy, I was talking to my cousin about earthquakes in Japan this week.

But we had just seen Mad Max and one of the trailers was that San Andreas one, so it's understandable why we got to that subject, I think.

Anyway, I feel like there is always a new earthquake now. We're seeing lots of activity lately, aren't we?

I hope people there are safe. On one hand, they're used to it and know exactly how to behave in case of an emergency, which is good. On the other hand, it is still dangerous and it can destroy a lot of things...

Sending positive thoughts to Japan.

S&F, OP.

Has anyone seen the testimonies over on EMSC? They are pretty scary, I thought when an earthquake was this deep, it would hardly be felt?
The nearest report is 839 km away and the furthest is 6148 km away? Felt Reports
857 km from epicentre from link above...

On 36 floor of The Prince Hotel, Shinagawa. The building was swaying for around 5 minutes after the earthquake. This could be perceived both visually and by "squeaking" of building as it swayed.

Wiki

In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers).[16] These seismically active areas of subduction are known as Wadati-Benioff zones. Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.[17]

a reply to: TrueAmerican

Thanks, TA. Very useful graphics. (The slab profile.) And yes, in respect of larger events around that region it's wise to keep an eye on things -- especially with that triple junction just a little ways north.

a reply to: whatnext21
Deep focus quakes can be felt at long distances if they are powerful enough.

From the General summary page at USGS for today's 7.8 Mw event, there's the following:

Earthquakes that have focal depths greater than 300 km are commonly termed "deep-focus". Deep-focus earthquakes cause less damage on the earth’s surface above their foci than is the case with similar magnitude shallow-focus earthquakes. Large deep-focus earthquakes may be felt at great distance from their epicenters. The largest recorded deep-focus earthquake was a 2013 M 8.3 earthquake that occurred at a depth of 600 km within the subducted Pacific plate beneath the Sea of Okhotsk, offshore northeastern Russia. The M 8.3 Okhotsk earthquake was felt all over Asia, as far away as Moscow, and across the Pacific along the western seaboard of the United States. Over the past century, 66 earthquakes with a magnitude of M7 or more have occurred at depths greater than 500 km; three of these were located in the same region as today's event. The largest nearby event at these depths was a 1968 M 7.3 earthquake, several hundred kilometers to the south of this earthquake.

(Bolding mine.)

Besides their comments about how far away these quakes can be felt, I've also highlighted the fact that such deep M 7-plus quakes are pretty rare and today's is only the fourth in that same region during the past 100 years.

It would be interesting to find out if any of the other three turned out to be foreshocks, but that could take some digging.

a reply to: 0bserver1

Generally speaking, tsunamis from sub-sea quakes have two primary causes:
-- vertical displacement of the sea floor and/or
-- sub-sea landslides.

The first was the cause of the Japan event in March 2011, the Sumatra "Boxing Day" event in 2004 and most other very large quake/tsunami events that have been recorded. Basically, a large section of sea floor is displaced vertically (up or down) due to a movement along a subduction zone. This causes a change in the entire column of water above and the subsequent movement of the water leads to the tsunami (or tsunamis, as there are often several). And as the water may be very deep, that column of water is massive and represents an enormous amount of energy.

The area of sub-sea "real estate" involved can be very large, and with huge quakes in the high M8 range or above it can be many thousands of square miles. Because of this, the wave length of the tsunami can be very long (even 100 miles), which is why in the case of the Japan event (for example), we saw videos of the tsunami/s just continuing to build higher and higher, sometimes for several minutes. Because that very-long-wavelength wave is still coming in.

The last big tsunami event in the lower 48 of (today's) USA was on Jan 26, 1700. In the region of the PNW, from Vancouver Island, BC, all the way down past Washington, Oregon and Nth California, the tsunamis came ashore at heights up to 100 feet. Then, after crossing the Pacific Ocean, tsunamis from the same quake inundated coastal villages in Japan about 10 to 12 hours later. That's how we know the exact date -- from the Japanese records.

Sub-sea landslide tsunamis tend to be very different in character. In this case the land mass is generally much smaller and also it affects a more limited volume of water. So, these tsunamis have a shorter wavelength. They can still be very destructive to nearby regions but do not carry as much energy as the huge ones like Japan had. Also, because they have less energy, these types of tsunamis dissipate far sooner.

There are other causes of tsunamis as well.

Undersea volcanic eruptions, if very explosive, can create regionalized tsunamis. So can landslides from land into the sea. Again, these can be massively destructive in the local region but do not travel huge distances (as destructive waves) as they lack the energy to do so.

When I say "regionalized", I don't mean just within a couple of miles or so. The bigger events can be destructive even to seaside places hundreds of miles away. But that is a lot different from the subduction-generated tsunamis, which can be deadly even several thousand miles away.

Finally, there are tsunamis caused by impacts of objects from space, such as asteroids. Because of their extremely high velocity and great mass, large impacts can generate gigantic tsunamis as the amounts of energy involved are also huge. Fortunately the really big impacts are rare.

My rainmeter earthquake map says that the depth is 677.56km. The deeper it is, the less effective/destructive right?