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Question of the Day
Question
How does a seismograph work? What is the Ricter Scale?
Answer
A seismograph is the device that scientists use to measure earthquakes. The goal of a seismograph is
to accurately record the motion of the ground during a quake. If you live in a city
you may have noticed that buildings sometimes shake when a big truck or a subway train rolls by.
Good seismographs
are therefore isolated and connected to bedrock to prevent this sort of "data pollution".
The main problem that must be solved in creating a seismograph comes from the fact that when the
ground shakes, so does the instrument. Therefore most seismographs involve a large mass of some sort.
You could make a very simple seismograph by hanging a large weight from a rope over a table.
By attaching a pen to the weight and taping a piece of paper to the table so that the pen can
draw on the paper, you could record tremors in the earth's crust (earthquakes). If you used a roll of
paper and a motor that slowly pulled the paper across the table, you would be able to record tremors
over time. However, it would
take a pretty large tremor for you to see anything. In a real seismograph,
levers or electronics are used to magnify the signal so that very small tremors are detectable.
A big mechanical seismograph may have a weight that weighs 1,000 pounds or more, and it drives
a set of levers that significantly magnify the pen's motion.
The Richter scale is a standard scale used to compare earthquakes. It is a logarithmic scale, meaning
that the numbers on the scale measure factors of 10. So, for example, an earthquake that measures 4.0
on the Richter scale is 10 times larger than one that measures 3.0. On the richter scale, anything below 2.0
is undetectable to a normal person and is called a microquake. Microquakes occur constantly. Moderate earthquakes
measure below 6.0 or so on the Richter scale. Above 6.0 are earthquakes that can cause significant damage. 8.9
is about the maximum quake ever measured.
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