A sort of omnibus

It’s been a while since I’ve posted here, so here’s an attempt to catch up (in a rambly, notes-to-self sort of fashion) — four things in chronological order:

1) AGU

This year’s Fall AGU meeting was chockablock with good stuff. As usual, the whole thing was a bit of a sensory-overload blur, but here are the main things that struck me:

  • Noise. Lots of stuff about seismic noise. A number of presentations on the use of seismic noise to calculate an equivalent seismogram between two stations, using cross-correlation — seems weird at first, then starts to make sense when you think about it. The idea is that if the noise you’re recording at your seismic stations reflects a bunch of randomly distributed sources coming from all sides, then some of that noise will actually be picked up more than one station, and will show up as correlated noise between the two — but it’ll be affected by the propagation path from one station to the other. Averaging over all directions, then, the cross-correlated noise spectrum ends up looking very much like a seismogram! Seismology without sources — groovy.
  • More noise — specifically, the Earth’s “hum”. Apparently there’s a part of the seismic noise spectrum that can be localized to the oceans, and has seasonal variability — during stormy times of year, the ocean is actually communicating significant seismic energy to the solid Earth.
  • Another rather startling result is that it seems to be possible to predict how big an earthquake is going to be before it’s finished happening — at least, that’s what’s implied by the ability to predict an earthquake’s magnitude by the first 4-5 seconds of its arrival. I wonder if this breaks down at very high magnitudes?
  • Lots more stuff that was of immediate interest to me — there does seem to be a difference between eastern and western Ontario in more data sets than just ours. The Superior Province isn’t so uniform after all.

As per usual, I left AGU energized and full of ideas — and then promptly took the holidays off and forgot two-thirds of it. Well, such is life.

2) The Sumatra earthquake and tsunami

The biggest earthquake, and perhaps the worst natural disaster, to happen in my lifetime. I found myself alternating between being appalled and being professionally fascinated — that thing was huge, as the calculated rupture on the USGS website shows. So many preventable deaths; with a warning system in place, I’d guess at least half of the dead could’ve been saved. The size and type of the earthquake are about the same as that of the Cascadia megathrust that B.C. and the Pacific Northwest are, with good reason, worried about — this could’ve been us, too, and one day it will be.

3) POLARIS Ontario workshop

Two weeks ago, there was a workshop on the Ontario project I’m participating in, out in Kingston. A small meeting, but a good mix of people, and a friendly venue in which to introduce my grad student to the milieu, I thought. There was some interest in our result that there’s a change between eastern and western Ontario — everything interesting seems to be happening in the middle of a gap in which there aren’t any stations, so hopefully some will be put in to plug the hole. I should really post on that result, incidentally.

4) Term, again

This term, I’m teaching Exploration Seismology, and generating much of it from scratch in the process. It’s a lot of work, but an interesting sort of work, and hopefully it’ll save me a bunch of time and effort next year. Practical courses like this are a balancing act — I want to get the theory right, but I also want the students to learn some immediately useful skills for the working world. A lot of our students are going into the oil industry nowadays — part of our role is to help their job prospects, after all.

It does feel a bit precarious, trying to teach a reasonably complete geophysics program with only two geophysics faculty. But I think we do a creditable job, overall, and my colleague Ian deserves the bulk of the credit for that — he even carried the whole program himself for a brief period. I have no idea how he managed.

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5 comments so far

  1. John Vidale on

    I’ve never posted to a blog on blogs.com before, seems like a nice format.
    I was impressed by the same top three as you – Campillo’s noise cross-correlation, Romanowicz’s hum, and Kanamori and Allen’s rapid source magnitude estimation.
    I bookmarked this – do you know of other seismology blogs?

  2. Andrew Frederiksen on

    Blogs.com is actually TypePad — the same software as Moveable Type, but they provide the hosting (you can chose blogs.com or typepad.com domains). There’s no free version, unlike LiveJournal, but I like the clean design — I’m a bit of a sucker for nice layout and typography. One of these days I’ll splurge and buy the full set of Edward Tufte’s books.
    It’s funny how AGU works that way — a huge meeting, but there’s always a buzz that tells you what’s big, even if you don’t hear it yourself. I actually missed hearing the Kanamori/Allen result first-hand, but I heard something about it, and then I had the good fortune to sit next to Richard Allen on the flight back, and heard the rest. It’s a marvellously counter-intuitive result.
    As for other seismology blogs — I haven’t found any yet, though I haven’t done any extensive digging beyond a little preliminary google work. If I find anything, I’ll let you know, and it’ll probably end up in the sidebar on the left.

  3. John Vidale on

    Regarding the Allen/Kanamori work – I think it is a bit over-hyped. I’m sure it is useful, but it probably amounts to being able to tell a big earthquake is happening by the time it is a quarter to a half over. Certainly, many huge earthquakes remain relatively small for more than 10 s, and it probably is impossible to tell whether they will continue to grow ahead of time. There is only a weak correlation between the initial time functions and the eventual moment for large datasets. I could be wrong, though.
    The format is easy on the eyes. I think I prefer LiveJournal, mainly because the students at UCLA show up more there than here. They are even more underfoot on Xanga and FaceBook, but those seem superficial and gaudy. LJ also has various levels of privacy for posts, although I don’t use them much.
    I’ll have to remember to check here from time to time.

  4. Andrew Frederiksen on

    A friend of mine actually set up an RSS feed of this page on LiveJournal, which might be useful: http://www.livejournal.com/users/seismology_log/

  5. John Vidale on

    Added the link to my LJ friends list. Good idea.


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