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A seismograph located in the Dow Environmental Sciences and Engineering
Building has recorded a magnitude 8.0 earthquake just off the Pacific
island kingdom of Tonga.
The
quake occurred shortly before noon Wednesday (Houghton time). You
can see the record at the web site http://www.geo.mtu.edu/UPSeis/MTU_Seismograph/
.
This
web site is updated every 10 minutes (you may need to refresh your
browser). Eventually, the earthquake record will be replaced with
newer data, but it will be visible for the next 20 hours at least.
So
why is there a seismograph on the ground floor of the Dow Building
(and another one in the Houghton Middle School)? "Earthquakes
send out seismic signals, and these, if the earthquake is large
enough, are recorded around the world. Witnessing the recording
of a large earthquake can be an exciting event, no matter where
it occurs," says Wayne Pennington, chair of the Department
of Geological and Mining Engineering and Sciences. The seismograph
in the Dow Building is in a vault where it is relatively isolated
from building vibrations and air currents, but you can see the seismograms
it creates on the seismograph website.
This
site is automatically updated every 10 minutes; you might need to
refresh your browser to see the changes. If you go to the seismograph
web site within 20 hours of the earthquake's occurrence, you will
be able to see the seismogram it created. The seismogram from this
earthquake will be over-written with new data (presumably less interesting)
starting at 8 a.m. on Thursday, but the later aftershocks (coming
in over a period of several hours) will be visible through most
of the afternoon. The data are saved in electronic format and can
be studied at any time. A seismogram of the tragic 2004 Sumatra
earthquake is displayed, at a reduced amplification and shortened
time scale, at http://www.geo.mtu.edu/news/26_DEC_2004.html
.
The
data is displayed in two formats. The main one consists of a series
of four-hour strips, with the time compressed to fit across the
screen, and the second one shows just the most-recent 30 minutes
of data, in an expanded time scale, near the bottom of the screen.
Because this earthquake is so large, most of the first few hours
show the up-and-down oscillations of the earth (yes, here in Houghton)
as a solid band because the amplitude is so large. The later hours
will show the individual waves more distinctly, as they diminish
in size from traveling around the world multiple times. At the time
that this article is written, there were no large aftershocks recorded,
Pennington said, but you might expect to see one or two by Thursday
or Friday. The largest ones are typically about one-tenth the amplitude
of the mainshock.
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