The earliest seismoscope was invented by the Chinese philosopher Chang Heng in A.D. 132. This was a large urn on the outside of which were eight dragon heads facing the eight principal directions of the compass. Below each dragon head was a toad with its mouth opened toward the dragon. When an earthquake occurred, one or more of the eight dragon-mouths would release a ball into the open mouth of the toad sitting below. The direction of the shaking determined which of the dragons released its ball. The instrument is reported to have detected an earthquake 400 miles away that was not felt at the location of the seismoscope. The inside of the seismoscope is unknown: most speculations assume that the motion of some kind of pendulum would activate the dragons.
Learn more: The Early History of Seismometry (to 1900)
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- FAQ
How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake hypocenter in a wave...
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How do you determine the magnitude for an earthquake that occurred prior to the creation of the magnitude scale?
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How do seismologists locate an earthquake?
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What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?
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How can an earthquake have a negative magnitude?
Magnitude calculations are based on a logarithmic scale, so a ten-fold drop in amplitude decreases the magnitude by 1.If an amplitude of 20 millimetres as measured on a seismic signal corresponds to a magnitude 2 earthquake, then:10 times less (2 millimetres) corresponds to a magnitude of 1;100 times less (0.2 millimetres) corresponds to magnitude 0;1000 times less (0.02 millimetres) corresponds...
What does it mean that the earthquake occurred at a depth of 0 km? How can an earthquake have a negative depth; that would mean it’s in the air. What is the geoid, and what does it have to do with earthquake depth?
An earthquake cannot physically occur at a depth of 0 km or -1km (above the surface of the earth). In order for an earthquake to occur, two blocks of crust must slip past one another, and it is impossible for this to happen at or above the surface of the earth. So why do we report that the earthquake occurred at a depth of 0 km or event as a negative depth sometimes?First of all, the depth of an...
Seismometers, seismographs, seismograms - what's the difference? How do they work?
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How can I make my own seismometer?
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What is a Geoid? Why do we use it and where does its shape come from?
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