Subject: Re: What's the truth? Are EQs really on the increase or not?
From: astephan@presby.edu (Andrew Stephan)
Date: Thu, 5 Dec 1996 01:24:35 GMT
In article <32A5CE5E.439F@ix.netcom.com>,
Judson McClendon wrote:
>I keep reading and hearing statements something like "according to the
>USGS, large EQs have been getting more frequent..." or some such.
Someone was lying to you - either that, or totally misrepresenting the
facts. Scientific earthquake detection and measurement is something
relatively new - it's only been going on for a hundred years or so.
Detection capabilities are improving all the time, so smaller
(which means more!) earthquakes are able to be detected. This does not
mean that more actually occuring. This is basically the point made below.
For some strange reason, the public seems to prefer the idea that
earthquakes are becoming more common. I don't know why. I would be
quite happy if damaging earthquakes were becoming rarer, myself.
Earthquake records clearly demonstrate that the average level of
occurence of earthquakes is constant over the long term. When you tell
this to people, they seem disappointed. A lot of them seem to think
seismologists are trying to hide something...
>However, the USGS (http://wwwneic.cr.usgs.gov/) has a text file saying
>there is NO increase. It says that the only increases observed are that
>more 'minor' EQs are detected because of more/better instrumentation.
>But the data in the file only shows EQs of 7.0> and is a few years out
>of date. Just what IS the truth concerning significant (6.0>) EQs?
Those are not any more common. Places like New Zealand, Japan, and
California in the US that have decent historical and/or scientific
records clearly demonstrate *no* longer term increase in signifigant
earthquakes. Actually, of the largest half dozen or so earthquakes
recorded by science, none have happened within the past several decades.
Given that people have only been actively measuring earthquakes for
what?, a century, if anything, a more reasonable argument might be that
large earthquakes are actually becoming *less* frequent. All the
evidence says that this is coincidence/random luck and not anything
signifigant.
Andrew
>--
>Judson McClendon judsonmc@ix.netcom.com
>Sun Valley Systems http://www.netcom.com/~judsonmc/sunvalley.html
Subject: mentors needed
From: jhutton@nths.covis.nwu.edu (James Hutton)
Date: Wed, 04 Dec 1996 21:46:25 -0600
My name is Rory Wagner. I am a high school Earth Science teacher at the
(recently) infamous (Time Magazine) New Trier High School. Our school is
involved in a NSF grant project with Northwestern University. We're
trying to see if our networked classroom, the use of some specially
adapted visualization software, and a curriculum that involves "project
science" (doing science instead of just learning about what has already
been done) instead of traditional lecture-lab-demo, will make any
difference in the quality of science education.
I'm looking for oceanographers, astronomers, meteorologists and
geoscientists (and interested/enthusiastic grad students) to act as
"Mentors" for various student projects. These mentors will assist my
students in their explorations, not by "giving all the answers" and
spending lots of time explaining basics, but by asking questions about
student developed research proposals, helping groups with their data
collection, and/or general research methods. Basically, to help keep the
kids "on the track" that I am laying down for them, and, hopefully,
providing professional expertise/insights when appropriate. I'm modeling
this on the "graduate type" of thesis research project, which is familiar
to all of you in some form. I'm hoping this will not be a time intensive
kind of involvement, and will primarily involve email communication on a
regular basis for the extent of the project.
If you are at interested in helping, please respond by email, and I will
send you more detailed information.
--
Rory Wagner
New Trier High School
385 Winnetka Ave
Winnetka, Il 60093
wagner@covis.nwu.edu
Subject: Re: China Lake
From: S Krueger
Date: Wed, 4 Dec 1996 22:52:32 GMT
In article Andrew Stephan, astephan@presby.edu
writes:
>Andrew Stephan wrote:
[snip]
>> Apart from anything else, it would be rather apparent if the earthquake
>> was not, in fact, an earthquake, and actually a nuclear test
[snip]
>> The difference between a nuclear explosion
>> and an earthquake is usually readily apparent to seismologists, or so I'm
>> told.
[snip]
>My understanding, is that the wave patterns are very different.
The main difference is that P waves from explosions (whether nuclear or
quarry blast) show compressional first motions in all directions.
Earthquakes are generally caused by fault slip, which results in
alternating quadrants of compressional and dilatational first arrivals.
Nuclear explosions also tend to show a collapse event as the enormous
hole which was created in the earth collapses from above. Any "event"
which is big enough to be detected by a significant number of global
seismometers will be easily distinguishable as an explosion or an
earthquake.
>What makes things
>more complex is when the nuclear tester decides to try to make it hard to
>tell if it was an EQ or a nuke. There are all sorts of tricks that can
>be done with this. Actually, one method used to hide the number of
>explosions (simultaneous or very near simultaneous detonation of multiple
>devices in a relatively small area) creates multiple sources of waves
>from very nearby locations. When you get this, you don't have that
>single wave thing anymore.
I hadn't heard of this before, but I would think you'd be able to
"unscramble" the multiple sources if you had teleseismic records from
several azimuths. Such practise would also put the tester in danger of
the combined "event" exceeding the agreed-to limits on the size of
nuclear tests. In general, the object of sneaky seismic tests was to hide
the size, not the number, of nuclear tests. This is because of the
established upper limits in the Test Ban treaty.
>Another interesting thing is a method for
>hiding a 20kT or so explosion. This is just a theory; I don't know if
>anyone has tried this, if some country has, they probably aren't going to
>talk about it. The method involved exploding the thing in a large cavity
>(of a very specific size) dug out especially for it. I don't recall the
>details, but there was some way (theoretically) to minimize wave
>transference to the ground and cause as much destructive wave
>interference as possible.
Not just a theory, but a common practice in the 60's and 70's. By
exploding the device in a large cavity you effectively minimize the
energy which is transmitted into the surrounding rock (air is much more
compressible than rock).
I believe Jack Everndon of the USGS had established, way back in the
70's, that existing seismic technology could detect even cave blasts
which exceeded the Test Ban limits with a small array outside the borders
of the old Soviet Union. For obvious political reasons (the rhetorical
value of maintaining an "evil enemy") his suggested detection array was
never assembled.
*******************************************************************
* S Krueger (skrueger@arco.com) * *
* This message is personal and does not * This Sace For Rent *
* reflect the opinions of my employer * *
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