Eruptions

Friday Flotsam

Not much in volcano news, however a lot of earthquake news this morning.

Did anyone else notice that two M6+ earthquakes occurred last night within one minute of each other last night (eastern daylight time)? The first was in the Banda Sea near Indonesia at 01:51:19 UTC (M6.8), the next was in northern Qinhai in China at 01:52:06 UTC (M6.2). I’m guessing that is just the sort of coincidences that occur when you have thousands of earthquakes globally a week, but still an interesting coincidence. There was also a series of earthquakes, all less than M3.7, last night in Oklahoma of all places. Not exactly in a hotbed of seismic activity.


Halema`uma`u Crater in March 2008.

Back in volcano-related news, Hawai’i 24/7 has a post about how the USGS/HVO goes about sampling the ash emitted from the Halema`uma`u Crater. The short answer: buckets. The fun facts in the article include estimates of the amount of ash and lapilli emitted since the Halema`uma`u eruption started last year:

* Total weight ejected during the eruption: 2,200 tons
* Total weight ejected during the 8 big explosive eruptions: 1,800 tons
* Total weight ejected between big explosive eruptions: 400 tons

Not bad. It shows that at Kilauea, most of the ash/lapilli ejected comes from the big events (over 80%) — so any time you see ash/lapilli layers in the rock record for a basaltic volcano, you might really be seeing very discrete events rather than a long period of activity. That is why observing the modern can unlock the past.

Comments

  1. #1 cicely
    August 28, 2009

    Your “a series of earthquakes” link goes to Page Not Found.

  2. #2 Erik Klemetti
    August 28, 2009

    Thanks for catching that Cicely … It was a missing quotation mark. Should be fixed now.

  3. #3 mjkbk
    August 30, 2009

    Interestingly, every single one of the eight earthquakes near Oklahoma City occurred at the exact same latitude and longitude–35.566 -97.29–in what looks like a business parking area of some sort. What the heck?

  4. #4 MadScientist
    August 30, 2009

    @mjkbk: Most of the time you’ll get some movement from pretty much the same place every few minutes and that sort of activity can go on for days or weeks. If the events were separated by many months or years then that would be less usual – but you also need to keep in mind that the exact epicenter usually cannot be determined from the seismometer recordings with any great accuracy.

  5. #5 spike
    September 3, 2009

    Fun with math: the chance of having two magnitude 6 or greater earthquakes occur with a minute of each other (ignoring triggered earthquakes) is about 4% per year.

    There are about 150 6+ eqs per year. The chance of a earthquake of that size occurring in a particular minute is about 150/(365*60*24), and so to have one occur in 150 chosen minutes, the chance is about 150^2/(365*60*24)= .04.

    (For magnitude 5+, you are better off estimating the chances of an eq not occurring in a given minute first- There are about 1500 per year, so the chance of one not occurring in any minute is (1-1500/(365*24*60))=.997, chance of none occurring in 1500 chosen minutes- .997^1500= .014, So the chance of two 5+ eqs occurring with one minute of each other in any given year is about 1-.014= .986.

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    December 14, 2010

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