Magnitude-6.5 earthquake - Southern Japan

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http://www.stuff.co.nz/world/asia/78950651/strong-quakes-hit-southern-japan-nuclear-plants-safe-dozens-injured

At least three people were killed and 45 injured by a magnitude-6.5 earthquake that knocked down houses and buckled roads in southern Japan on Thursday night.
...
The epicenter was 120 kilometers northeast of Kyushu Electric Power Co.'s Sendai nuclear plant, the only one operating in the country. The plant was unaffected.
 

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  • #2
davenn
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M6.2 - 7km SW of Ueki, Kyushu, Japan
32.849°N 130.635°E depth=10.0 km

This M6.2 mainshock was followed by a M6.0 and many other aftershocks

160413-14  UT M6.2, 6.0 and other aftershocks Kyushu, Japan.JPG




Dave
 
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Astronuc
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On Yahoo (AP) - Strong quake hurts 45 in south Japan; people may be trapped
https://www.yahoo.com/news/powerful-earthquake-hits-south-japan-134654662.html [Broken]
It is reported as Mag 6.5

The quake struck at 9:26 p.m. at a depth of 11 kilometers (7 miles) near Kumamoto city on the island of Kyushu, the Japan Meteorological Agency said. There was no tsunami risk.
Shallow, but inland.

USGS - M6.2 - 7km SW of Ueki, Japan
http://earthquake.usgs.gov/earthquakes/eventpage/us20005hzn#general
2016-04-14 12:26:36 (UTC) - 9:26 pm local time.
Location: Lat 32.849°N, Long 130.635°E
Depth: 10.0 km (6.2 mi) - shallow

Followed last by this about 20 km SSE of the Mag 6.2
M6.0 - 5km E of Uto, Japan
http://earthquake.usgs.gov/earthquakes/eventpage/us20005i1a#general
2016-04-14 15:03:47 (UTC)
Location: Lat 32.679°N, 130.724°E
Depth: 10.0 km (6.2 mi) - shallow
 
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Earthquake upgraded:

A powerful earthquake which struck southern Japan early Saturday, barely 24 hours after a smaller quake hit the same region and killed nine people, has been upgraded to a magnitude 7.3.

The quake shook the Kumamoto region at 4.25am Saturday (NZ time), and several aftershocks followed.
(changes reflected in the link to the article in the previous post)
 
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Earthquake upgraded:



(changes reflected in the link to the article in the previous post)
Lets hope 7.3 is as bad as it gets, they could use a break.
 
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davenn
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Astronuc
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Earthquake upgraded:

(changes reflected in the link to the article in the previous post)
That's pretty impressive to have a 7 followed closely (20 to 22 minutes later) by a couple near Mag 6.0, and shallow at that.

5.7 2km NW of Ozu, Japan 2016-04-15 16:45:56 UTC Depth 10.0 km
5.8 2km ENE of Uto, Japan 2016-04-15 16:44:06 UTC Depth 10.0 km
7.0 1km WSW of Kumamoto-shi, Japan 2016-04-15 16:25:06 UTC Depth 10.0 km

That will certainly add to the damage.
 
  • #10
davenn
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There's more interesting geological/tectonic happenings with these events in that region
that became blindingly obvious when I was looking close in at the SW Japan area and the earlier events

notice where the quakes have occurred .....
The SW end of a very long topographical feature in the land. Thought to myself, this has got to be a major fault system
looks just like the Alpine Fault in the South Is. of NZ and like sections of the San Andreas Fault system in California ( to name a couple)
Japan quakes.jpg



After some digging I have found that this long fault zone is called the Japan Median Tectonic Line
It's the longest continuous fault system in Japan
https://en.wikipedia.org/wiki/Japan_Median_Tectonic_Line

Tectonic map of southwest Japan.jpg


At 5 - 10 mm/yr, the motion rates on this system are substantially less that the main plate boundary far to the southeast
which are around 55mm/yr. The main boundary taking up and releasing the majority of the accumulating stress in the region.
The MTL ( Median Tectonic Line) is a right lateral strike-slip fault. That means, if you are standing on one side of the fault and
looking across to the other side, that other side is moving to the right relative to you.


Dave
 
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it is still the 7.0 as originally listed on the USGS site

I wouldn't take too much faith in places like
http://www.stuff.co.nz/world/asia/7...ttles-southern-japans-kumamoto-for-second-day

the media never get anything correct


Dave
"The Japan Meteorological Agency initially said the Saturday quake was 7.1 magnitude but later revised it up to 7.3. The quake was 22 times more powerful, in terms of energy released, than Thursday's shock, according to the USGS website's Magnitude Difference Calculator."
 
  • #12
Astronuc
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Second big quake hits southern Japan, damage and death toll mounts
https://www.yahoo.com/news/second-big-quake-hits-southern-japan-people-flee-010937704--finance.html

A lot of damage - again.

The USGS world map doesn't show the particular fault like Dave's map does. But it's one of several faults caused by the Philippine plate pushing into the Eurasian plate, and Philippine plate is being pushed by the Pacific Plate.

http://earthquake.usgs.gov/earthquakes/tectonic/images/philippinesea_tsum.pdf
 
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Astronuc
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Adding to the anxiety in Kumamoto,
There was a small-scale eruption at Mount Aso, an active volcano in Kumamoto Prefecture, at around 8:30 a.m. on April 16, with smoke billowing into the sky approximately 100 meters from the No. 1 crater of the volcano's Nakadake peak, the Japan Meteorological Agency (JMA) announced. The agency is keeping its volcanic alert for Mount Aso at Level 2, warning people against approaching the crater.
http://mainichi.jp/english/articles/20160416/p2a/00m/0na/017000c

Frequency of Kyushu quakes highest on record for Japan inland
http://mainichi.jp/english/articles/20160417/p2a/00m/0na/017000c

I was wondering about the swarm of earthquakes in Kumamoto. I don't remember seeing a swarm like that in Japan with other earthquakes. Usually there are a few aftershocks. Now in addition to the quakes, Mt Aso has had a minor eruption.

According to the agency, the number of earthquakes of at least magnitude-3.5 in Kumamoto and surrounding areas since the first M-6.5 temblor struck on the night of April 14 had hit 162 by 8:30 a.m. on April 17. The figure exceeded that for temblors following the M-6.8 Chuetsu earthquake in central Niigata Prefecture in 2004, which had held the previous high. The agency began observing the frequency of earthquakes measuring at least M-3.5 in 1995.

The number of quakes has increased since the M-7.3 main quake in the early hours of April 16, JMA officials said.
I do remember the quake in Darfield (Christchurch) NZ did have thousands of earthquake aftershocks.
 
  • #14
davenn
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I was wondering about the swarm of earthquakes in Kumamoto. I don't remember seeing a swarm like that in Japan with other earthquakes. Usually there are a few aftershocks.
For others reading this.....
There is a difference between a "swarm" and an "aftershock sequence"

1) a swarm refers to a set of events maybe 10's to a few 100 events where there is no significant main shock. Swarms would rarely contain events of higher magnitude ~M5.5 or greater. They would commonly consist of events in the M0 to M4.5 range ( A caveat .... event magnitude can actually go below M0 ... eg M0.5 ... swarm or otherwise)

2) An aftershock sequence follows a main shock. The mainshock can be small events say a M 4.5 and the aftershocks will be smaller than that M2's M3's etc.
The larger the main shock the more aftershocks there will be. A significant main shock, say a M6.5 could produce 100's of smaller aftershock events
An eg M7.5 or greater can often produce 10's of 1000's of recorded aftershock events particularly for shallow events ~30km or less.
The in general, deeper the main shock the main shock the smaller the number of aftershocks. Very deep main shocks may produce none to just a handful of recorded aftershocks.
A general rule for large main shocks, say around M7.0 and greater, an aftershock of up to 75% of the size of the main shock can be expected in the following 48 hours. Doesn't always happen, sometimes not at all, sometimes within the week following the main shock

Some sequences have foreshocks, then the main shock, then the aftershock sequence.
When foreshocks occur, it is not known if the event(s) is a foreshock or the main shock till some time has passed to see if a larger event occurs
This was apparent with the M6.2 ( original main shock this thread discussed) It was considered a main shock even after the M 6.0, the second largest event occurred but both those events were relegated to being foreshocks once the M7+ event occurred. That doesn't occur overly often and usually the foreshocks ( if any) are significantly smaller than the mainshock.

OK there's the seismology lesson for the nite, all the way from the East African Rift ( my current location)

cheers
Dave
 
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OK there's the seismology lesson for the nite, all the way from the East African Rift ( my current location)
Great location for a seismology lesson. :smile:
 
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davenn
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1) a swarm refers to a set of events maybe 10's to a few 100 events where there is no significant main shock. Swarms would rarely contain events of higher magnitude ~M5.5 or greater. They would commonly consist of events in the M0 to M4.5 range ( A caveat .... event magnitude can actually go below M0 ... eg M0.5 ... swarm or otherwise)
From USGS - An earthquake swarm is "a series of minor earthquakes occurring in the same area and time, none of which may be identified as the main shock or with the same fault."

I tend to use the term more liberally for a geographically localized group of earthquakes, e.g., the recent group around Vanuatu, or Chignik Lake, Alaska.
 
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