Friday, September 14, 2007

Serial Earthquake Binge in Sumatra

Blogging always means sharing, and here is a couple of recent e-mails from my brother who runs a large USAID project at Banda Aceh in Sumatra. My daughter is taking Geology 101 in college and we both watched a Nova PBS show on "super-volcanoes," one of which is Lake Toba in Sumatra about 400 miles south of Banda & not too far from the earthquakes my brother recounts with his first e-mail:
Just so no one worries needlessly, the 8.4 quake off the west coast of
Bengkulu province last night was maybe 500 miles from here and I did not
even feel it. I did feel the "aftershock" of 7.9 this morning from an
epicenter north of the original quake. It was kind of a queezy, woozy quake
which caused the chandelier in our house (they like those here) to swing in
a circle very slowly about 6 inches of arc outside of hanging still. But
many people did not feel it at all. Anyway, no damage, no tsunami here.

There's a quake that you can feel about every four months. Sometimes
there's a deep, nearby quake rather close. Sometimes its a more powerful,
far away quake like this one. Each has its own sort of feel-from abrupt,
repeated rythms like one I felt last year, to almost imperceptible swaying
like this one. My house made it through the 9.1 quake in 2004 that produced
the tsunami, so it should do OK in most other quakes. Makes life

A quake every four months is one thing. Two days later, he sent another e-mail:
Yesterday had earthquakes of 8.4. 7.9, and 7.1 in the same general region
off West Sumatra and Bengkulu, about 500 or 600 miles from here. Today
there was another, reported to be 6.4 on the Richter scale. I've never
heard of anywhere such a thing has happened before. What they are counting
as aftershocks are actually in the major quake range.

Of course, the Richter scale is a measure only of the total energy expended,
and tells you nothing of how that energy was focused. I heard, for example,
that the 8.4 quake lasted 3 minutes, so all that release of energy was
spread out over a long time, making it far less destructive than it it had
all been released within 30 seconds. Also, both the depth of the epicenter
and the nature of the fault network arouond there affect the nature of the
waves and hence the destructiveness of the quake. I myself felt a quake at
about 1.00am six months or so ago which started with about five or six quick
jerks, then nothing, then five or six jerks again, then nothing, then the
jerks again--as it these waves were coming in bursts. That was from a 6.5
quake on the North Sumatra-West Sumatra border. Yesterday, I did not feel
the 8.4 at all but did feel a gentle rolling, dizzy kind of movement during
the 7.9 quake (remember I am about 500 miles away). Every one of them is

This place is a seismologist's paradise. Most active place on earth. I
myself have seen (not too close) 3 major eruptions, the aftermath of a major
quake, and the results of history's most destructive tsunami while here.
Of course, where you are there are tornados. All these events make life
more interesting--I suppose because of the risk?

Of course, there is that old Chinese curse, "may you live in interesting times."

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