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Magnitude-6.5 earthquake - Southern Japan

  1. Apr 14, 2016 #1
    http://www.stuff.co.nz/world/asia/7...hern-japan-nuclear-plants-safe-dozens-injured

     
  2. jcsd
  3. Apr 14, 2016 #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
     
  4. Apr 14, 2016 #3

    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

    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
     
    Last edited by a moderator: May 7, 2017
  5. Apr 14, 2016 #4
  6. Apr 15, 2016 #5
    Not good...
    http://www.stuff.co.nz/world/asia/7...ttles-southern-japans-kumamoto-for-second-day
     
  7. Apr 15, 2016 #6
    Earthquake upgraded:

    (changes reflected in the link to the article in the previous post)
     
  8. Apr 15, 2016 #7

    1oldman2

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    Lets hope 7.3 is as bad as it gets, they could use a break.
     
  9. Apr 15, 2016 #8

    davenn

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  10. Apr 15, 2016 #9

    Astronuc

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    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.
     
  11. Apr 15, 2016 #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
     
  12. Apr 15, 2016 #11
    "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."
     
  13. Apr 15, 2016 #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
     
  14. Apr 17, 2016 #13

    Astronuc

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    Adding to the anxiety in Kumamoto,
    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.

    I do remember the quake in Darfield (Christchurch) NZ did have thousands of earthquake aftershocks.
     
  15. Apr 22, 2016 #14

    davenn

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    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
     
  16. Apr 22, 2016 #15

    1oldman2

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    Great location for a seismology lesson. :smile:
     
  17. Apr 23, 2016 #16

    davenn

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    indeed :)
     
  18. Apr 23, 2016 #17

    Astronuc

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    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.
     
    Last edited: Apr 23, 2016
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