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WEBVTT
Kind: captions
Language: en

00:00:06.620 --> 00:00:09.960
After the earthquake the Cypress Structure
collapsed.

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[The Cypress Structure is a two-tiered part
of the Nimitz Freeway.]

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People were trapped in cars.

00:00:14.030 --> 00:00:16.480
And people were working on the structure

00:00:17.100 --> 00:00:19.800
trying to free people,

00:00:19.980 --> 00:00:23.560
dismantle the structure so it wouldn't collapse and kill other people.

00:00:24.720 --> 00:00:28.800
And my colleagues Bill Bakun,

00:00:29.320 --> 00:00:33.300
and Grey Jensen, and John VanSchaack, and I'm probably leaving out others,

00:00:33.560 --> 00:00:36.860
realized that they could actually

00:00:37.660 --> 00:00:40.200
do what we now call "earthquake early warning."

00:00:40.200 --> 00:00:47.030
They put a[n] analog piece of equipment near
the epicenter of Loma Prieta.

00:00:47.030 --> 00:00:50.880
It sent its signal essentially at the speed
of light to Menlo Park.

00:00:50.880 --> 00:00:57.800
A simple analog circuit said, "If I see this
kind of amplitude I'm going to send a signal

00:00:57.800 --> 00:01:01.880
up to the Cypress Structure," where we had some sort of annunciator . . .

00:01:02.020 --> 00:01:03.340
I forget what it was.

00:01:04.320 --> 00:01:12.800
And it would give people on the structure,
I believe, on the order of 15 seconds of warning

00:01:12.800 --> 00:01:14.520
before a large earthquake.

00:01:14.520 --> 00:01:17.790
Large being magnitude M4.5 or something in
that neighborhood.

00:01:17.790 --> 00:01:20.060
I'm a little rusty on all this.

00:01:20.760 --> 00:01:23.920
It turns out that while it worked. . .

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First of all the earthquake, itself,
was pretty devoid of large magnitude aftershocks.

00:01:30.320 --> 00:01:33.540
I believe there was only one magnitude 5?

00:01:33.540 --> 00:01:39.280
But even so, the interest in this prototype
earthquake early warning system was to

00:01:39.340 --> 00:01:43.220
warn the workers that shaking was coming.

00:01:43.230 --> 00:01:46.360
There was no time for them to get off the
structure with 15 seconds.

00:01:46.360 --> 00:01:49.900
But [what] they were afraid of was that the structure

00:01:49.900 --> 00:01:52.720
was becoming unstable and was about to collapse.

00:01:52.720 --> 00:01:54.680
So if they knew it was an earthquake [shaking the structure]

00:01:54.680 --> 00:01:56.680
that was to be expected.

00:01:56.760 --> 00:01:58.660
But shaking without an earthquake . . .

00:01:58.700 --> 00:02:02.660
"We have a problem here," and they needed to get out of the structure.

00:02:03.720 --> 00:02:09.240
It was an interesting little side note to
earthquake early warning because it really

00:02:09.250 --> 00:02:15.099
didn't take off again for decades later, until
the quality of the instrumentation improved.

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