Seismometers, seismographs, seismograms - what's the difference? How do they work?
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 earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network. The earliest "seismoscope" was invented by the Chinese philosopher Chang Heng in A.D. 132. This did not, however, record earthquakes; it only indicated that an earthquake was occurring. The first seismograph was developed in 1890.
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 the mass, the recording device on the mass records the relative 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.
A seismogram is the recording of the ground shaking at the specific location of the instrument. On a seismogram, the HORIZONTAL axis = time (measured in seconds) and the VERTICAL axis= ground displacement (usually measured in millimeters). When there is NO EARTHQUAKE reading, there is just a straight line except for small wiggles caused by local disturbance or "noise" and the time markers. Seismograms are digital now - there are no more paper recordings.
Learn More: Glossary of earthquake terms
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How can an earthquake have a negative magnitude? 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)...
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? 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...
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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. Model Seismograph - Classroom Demonstration Build your own Seismograph Station Build Your Own Seismograph Amateur Seismology Homebuilt Seismograph FAQ
What was the first instrument that actually recorded an earthquake? What was the first instrument that actually recorded an earthquake?
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...
What is a Geoid? Why do we use it and where does its shape come from? What is a Geoid? Why do we use it and where does its shape come from?
A geoid is the irregular-shaped “ball” that scientists use to more accurately calculate depths of earthquakes, or any other deep object beneath the earth’s surface. Currently, we use the “WGS84” version (World Geodetic System of 1984). If Earth were a perfect sphere, calculations of depth and distances would be easy because we know the equations for those calculations on a sphere. However, the...
Related
How can an earthquake have a negative magnitude? 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)...
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? 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...
How can I make my own seismometer? How can I make my own seismometer?
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. Model Seismograph - Classroom Demonstration Build your own Seismograph Station Build Your Own Seismograph Amateur Seismology Homebuilt Seismograph FAQ
What was the first instrument that actually recorded an earthquake? What was the first instrument that actually recorded an earthquake?
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...
What is a Geoid? Why do we use it and where does its shape come from? What is a Geoid? Why do we use it and where does its shape come from?
A geoid is the irregular-shaped “ball” that scientists use to more accurately calculate depths of earthquakes, or any other deep object beneath the earth’s surface. Currently, we use the “WGS84” version (World Geodetic System of 1984). If Earth were a perfect sphere, calculations of depth and distances would be easy because we know the equations for those calculations on a sphere. However, the...