Re: pinhole Large Magnitude Earthquakes

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From: John or Jan Lahr (JohnJan@lahr.org)
Date: Thu Dec 09 2004 - 13:34:13 PST 

Message-Id: <6.2.0.14.2.20041209141701.0268a408@mail.comcast.net>
Date: Thu, 09 Dec 2004 14:34:13 -0700
From: John or Jan Lahr <JohnJan@lahr.org>
Subject: Re: pinhole Large Magnitude Earthquakes

Hi Rebecah,

The technique used up until the late 1960's for determining the magnitude
of an
Earthquake did not work well for events above about 8.5. The magnitude of
larger
events were often underestimated. The moment magnitude technique is
used to estimate the Richter magnitude whenever possible.

The USGS lists the largest events recorded since 1900 here:
http://neic.usgs.gov/neis/eqlists/10maps_world.html
The largest was along the coast of Chile in 1960: magnitude 9.5
The next largest was along the coast of Alaska in 1964: magnitude 9.2

Your students weren't totally correct, because the 1923 event in Japan had
a magnitude of 7.9.
http://neic.usgs.gov/neis/eqlists/eqsmajr.html
1923 Sep 1 Japan, Kanto
35.0 N 139.5 E 143,000 7.9 Great Tokyo fire.
There are photos here:
http://www.japan-guide.com/a/earthquake/
The magnitude of historic events such as this is always subject to change
with added study. The current "best" estimate of the magnitude of many
earthquakes is given on this page:
http://earthquake.usgs.gov/docs/sign_eqs.htm

Cheers,
John

At 02:03 PM 12/9/2004, you wrote:
>I have a question about earthquakes. My old textbook said that there has
>never been an earthquake recorded with a magnitude over 9.0. But my new
>textbook says that the 1923 Tokyo earthquake was 9.2 and the 1960 Chile
>earthquake was 9.5. Is this true? I (going on the information in the old
>textbook) told my students that there has never been a magnitude 9.0, and
>then they (being the smart alecs they are) pointed out that the book said
>I was wrong.
>
>So which is it?
>
>A confused,
>Rebecah Davis
>
>
>"The tragedy of science - the slaying of a beautiful hypothesis by an ugly
>fact."
>
>--TH Huxley
>
>
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