Measuring earthquakes in Japan

On Sunday night, a large earthquake struck underwater off the coast of Japan and gave the entire Tokyo area a good shake. Then, on Tuesday morning, the Tokai region was visited by a much closer earthquake which damaged the main expressway between Tokyo and Nagoya.

Both quakes were around 7 on the Richter scale, which sounded catastrophic to my friends in California, but they would not have been quite as panicked if they were using the Japanese scale. This is because the Richter scale measures the power of an earthquake at its source (magnitude), whereas the Japanese shindo scale measures its power at the surface (seismic intensity). The Japanese scale basically breaks down as follows:

  • 1 = Barely noticeable
  • 2 = Noticeable but not scary
  • 3 = Rattles unsecured objects
  • 4 = Knocks unsecured objects over
  • 5 = Damages rickety buildings
  • 6 = Damages earthquake-resistant buildings
  • 7 = The Earth cracks open; demons emerge; everyone dies

Each location would therefore report a different number from the same earthquake, based on the effects on the ground there. The Japan Meteorological Agency publishes a map showing the seismic impact of each earthquake at various locations, as well as its epicenter. Around Tokyo, Sunday’s quake was around 3 or 4 on the Japanese scale, largely as a result of the quake being deeper underground and farther offshore; Monday’s quake was even weaker for us, but folks in the Izu Peninsula area got to experience seismic effects in the 5 to 6 range.

The foreign media, being sensationalists, still love to use the Richter scale for everything, despite the fact that it serves little practical purpose other than scaring my parents.

31 thoughts on “Measuring earthquakes in Japan”

  1. Yeah, I started getting calls from the US about this as well.

    And, while the J-media did a good job on stating that this is not the type of quake that would result in another 東海地震, as the assumed local “pro” on anything earth science related, I’ve been bombarded by questions on this, even though my specialty is not anything at all related to seismology.

    But just in case there is confusion on this, in a nutshell, Izu actually rides on a separate tectonic plate than the rest on Honshu. This plate is subducting under Honshu. This results in a tremendous amount of friction between the plates. If they got locked up for a significant amount of time and that energy was suddenly released, then we would experience a catastrophic earthquake.

    But, Monday’s quake was completely localized to the subducting plate. That is, an internal fault moved, probably due to the forces of being pulled down below another slab of the Earth’s crust.

    Which is, as the media reported, no cause for alarm.

  2. “I started getting calls from the US about this as well.”

    I get calls and I’m not even near Tokyo.

    Loved that demons bit.

  3. Joe, according to Tom Weller, it’s the “Rictus Scale”, and scientists base the numbers on observed phenomena:

    Magnitude 0 – 3:
    Small articles in local papers

    Magnitude 3 – 5:
    Lead story on local news; mentioned on network news

    Magnitude 5 – 6.5:
    Lead story on network news; wire service photos appear in newspapers nationally; governor visits scene

    Magnitude 6.5 – 7.5:
    Network correspondents sent to scene; president visits area; commemorative T-shirts appear

    Magnitude 7.5 up:
    Covers of weekly news-magazines; network specials; “instant books” appear

    In the same book, “Science Made Stupid”, Weller also does an amusing take on who’s to blame for earthquakes. Check it out:

  4. > Both quakes were around 7 on the Richter scale, which sounded catastrophic to my friends in California

    6.5 and 6.8, respectively. As the scale is logarithmic in nature, rounding by even a few tenths results in huge differences.

    Also, when people say Richter scale, they most likely are referring to the moment magnitude scale, which essentially replaced it in the 1970s.

    > but they would not have been quite as panicked if they were using the Japanese scale.

    In addition to the shindo (震度), the above “Richter” magnitude scale is also used in Japan. However, they measure two different concepts, making it impossible to compare or convert between each other. The magnitude scale measures seismic energy, while the shindo measures the seismic intensity (how much it shakes).

  5. I received calls from my family in Europe, from Italy and Spain. I don’t know what the media informs over there but they though that Tokyo was totally destroyed…
    The first thing I listen to the phone was: “Are you OK? How many people dead? Do you have food?”…

    Just to make money increasing audience they don’t care to lie to people…

    Twitter and personal blogs resulted a better and more reliable source of information of what’s really going on here.

  6. “Twitter and personal blogs resulted a better and more reliable source of information of what’s really going on here.”

    Next time, I’m going to Twitter my family – “Building collapsed, no food, send money”.

  7. it’s all part of the plan to cull the population.
    Make Tokyo the capital, fill it up with superfluous people,
    create a temporary construction boom and then wait for the big
    one to finish everyone off, and then move the capital to somewhere else.
    Where is worthy ? Yapari Kyoto.

    Seriously though, anyone else thinking of getting out while they are still alive ?
    i’d feel bloody stupid if I died having had three warnings so close together.
    I feel pretty bloody stupid as it is anyway

  8. I got out long ago. There hasn’t been a decent (serious) earthquake in my city since 1748 or something like that.

  9. The hardest part of reporting back to home base for me is explaining that the number that my parents read in the news and the number where I am are different numbers.

    For people in their area, magnitude 6 and 7 are numbers that make the news, and thus have meaning to them. When I tell them that it was only only “seismic intensity 3.5” in my neck of the woods, I then have to describe to them how much stuff shook and for how long.

    So in the end, the numbers are meaningless, and I have to rely on anecdotes.

  10. On Tuesday I ran into the kids room and picked up the baby
    and my wife was protecting our daughter. So it felt pretty serious to us.
    We live in a 30 year old house (ancient !!) so I suppose we are risk-high.

  11. It was 7.3, but I believe it did so much damage because the epicenter was RIGHT smack in the middle of the city, as opposed to out in a rural area between major cities.

  12. Much much much worse. M7.3, which as has been noted is a whole heap worse than even M7.2, and Shindo 7, which is the top of the scale. It was felt from Kagoshima to Niigata, and woke me up hundreds of km from the site. Plus about 6,000 people died.

  13. The Kobe quake was very shallow, and the shock waves also bounced against Mt. Rokko and rolled back over the city. Of the three recent big quakes, the first was 340 km deep and the second was 23 km deep, so had a much bigger impact in the local area. Depth is more important than magnitude in determining the effects.

  14. But isn’t the depth factored into the M score, since it’s based on the strength at surface level?

  15. Roy, I don’t think so. The magnitude is the force at the epicenter. If it is 300 or 400 km under the sea, for example, an M7 can involve very little shaking at ground level. I have seen strong deep undersea quakes that had no shaking near the source and which registered, say, shindo 1 or 2 rather far away.

  16. Luckily that problem can be solved with cyborgs. The human brain keeps them from rebelling-at least at first.

  17. I dunno – have you seen what Cybermen do? Pretty lethal from the get-go.

    But the solution is simple: never construct a robot that is both stronger and more intelligent than humans. One or the other, but never both.

  18. I was never really a big fan of the Cyberman, possibly my least favorite of the major recurring Doctor Who villains.

  19. True, I never much liked them either. Daleks that could walk, basically. But pretty lethal (unless you got them near gold).

  20. Also, as much as I love the new Doctor Who show overall, I HATED the new version of the Cybermen. For no good reason he threw away their original and somewhat interesting origin, and replaced it with a lame Davros ripoff.

  21. Well, they kinda explained it away by having them be alternative universe cybermen. Still sucked. But then I found myself liking the New Who series less and less as fat fanboy Russell T Davies pandered to his homophilic lurv of The Doctor. Though to be honest I date the decline from when Jonathon Nathan-Turner took over (last season of Tom Baker). Who was never the same after that….

  22. Davies definitely got too fanboyish at times, but I’m VERY much looking forward to the next season, when Stephen Moffat takes over. He’s written the best episode every season of the new series so far – the more gothic horror type stories, somewhat reminiscent of the best days of the classic series.

  23. Ditto to Jade OC. Dr. Who was in it’s prime from second season Perwee to sixth season Baker. Nathan Turner ruined it. I think the new Doctor Who has been improving over time and am looking forward to the new producer.

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