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.

More like this

First off, I wanted to thank all of the Eruptions readers for making January the most popular month ever on this blog. I suppose I should give an assist to Yellowstone, but really, thanks for coming to the blog, reading the posts and engaging in all the great discussions that go on within its (…
We've arrived at Friday. The local time is 8:45 A.M. Set your watches accordingly. Batur, Indonesia Some news! More evacuations have been authorized near Mayon as the volcano continues to show signs of significant eruption. Activity has quieted some since Tuesday's explosion, but PHIVOLC still…
The collapse pit within the Halema`uma`u Crater at Kilauea taken January 7, 2010. Image courtesy of the USGS/HVO. Eruptions reader Boris Behncke pointed out that things are afoot in the Halema`uma`u Crater at Kilauea. To steal his description: " the lava lake returned triumphantly to the active pit…
Not sure how it was kept quiet for most of the week (well, at least to me), but geologists at the HVO have noticed a new lava lake in Halemaumau Caldera on Kilauea (Hawai'i). The lava lake is around 330 feet (~100 meters) below the crater rim and ~160 feet (50 meters) across with sections of…

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

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?

@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.

By MadScientist (not verified) on 30 Aug 2009 #permalink

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.