سوالات متداول در مورد سیسموگراف ها و پاسخ
آنها FAQ - Seismographs
?Q: What is a seismometer? What are seismographs? How do they work
A: A seismometer is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with "seismograph". Seismographs are instruments used to record the motion of the ground during an EQ--installed in the ground throughout the world and operate as seismographic network. The first one was developed in 1890. The earliest "seismoscope" was invented by the Chinese philosopher Chang Heng in A.D. 132. This did not record earthquakes, however. It only indicated that there was one occurring.
A seismograph is securely mounted onto the surface of the earth so that when the earth shakes, the entire unit shakes with it, EXCEPT for the mass on the spring which has inertia, and remains in the same place. As the seismograph shakes under (in the example below) the mass, the recording device on the mass records the realtive motion between itself and the rest of the instrument, thus recording the ground motion. In reality, these mechanisms are no longer manual, but instead work by measuring electronic changes produced by the motion of the ground with respect to the mass.
For further information see:
Seismographs: Keeping Track of Earthquakes
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?Q: What are seismograms? How do you read them
A: Seismograms are the records (paper copy) produced by seismographs used to calculate the location and magnitude of an earthquake. They show how the ground moves with the passage of time.
On a seismogram, the HORIZONTAL axis = time (measured in seconds) and the VERTICAL axis= ground displacement (usually measured in millimeters). When there is NO EQ reading there is just a straight line except for small wiggles caused by local disturbance or "noise" and the time markers.
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?Q: How is the movement of the seismometer converted into a seismogram
A: There are several ways:
- a pen drawing an ink line on paper revolving on a drum
- a light beam making a trace on a moving photographic film
- electromagnetic system generating a current that is recorded electronically on tape
Q: How can I make my own seismometer?
A: It is relatively easy to acquire the necessary materials and build your own seismometer. The links here are to various sources with information on how to build a seismometer. They range from very simple and inexpensive to sophisticated and pricey.
- Build Your Own Seismograph -Univ. of CA, Berkeley
- Build your own Seismograph Station - Redwood City, CA Public Seismic Network
- PEPP Instruments -Indiana University PEPP Earthquake Institute Home Page
- Seismometers You Can Build - list of resources from Princeton
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