After this activity, you should be able to:
- Understand how a seismograph works to measure the magnitude of an earthquake.
- Understand how and why engineers use a seismograph.
- Discuss methods to improve and re-engineer the model seismograph.
- Describe how a seismogram can help a community.
DOES THIS LOOK LIKE A SCIENTIFIC MEASURING DEVICE? COULD IT TELL US ANYTHING ABOUT AN EARTHQUAKE?
The first earthquake measuring device was a seismoscope, which was invented in 132 A.D. in China by philosopher Chang Hêng. It was a vase-like instrument with eight dragon heads (each holding bronze ball) lined up in the eight principle directions of a compass with an open-mouthed toad lined up beneath each dragon head. When an earthquake occurred, the dragon head which represented the direction of the earthquake would dislodge one of the bronze balls into the mouth of its corresponding toad. The fall of a certain ball allowed early scientists to determine the direction of the epicenter of the earthquake. Although the exact make-up of the interior cavity of this early seismoscope is not known, scientists believe that a pendulum was the primary sensing device that released the bronze ball from the dragon's mouth.
As the years progressed, earthquake measurement devices have become more sophisticated. Engineers work to design improved measurement devices to help people learn about and predict earthquakes. Today seismographs are used to determine the force of an earthquake. The device measures the seismic waves given off during an earthquake. The way a seismograph works is that paper is wrapped around a drum, and a stylus (or pen) which is very sensitive to even slight movement, marks the movement of a needle creating a seismogram — a record of the earthquake. Therefore, the tremendous seismic waves caused by an earthquake result in the needle vibrating back and forth over a piece of paper to create a unique seismogram for each earthquake that occurs. Scientists and engineers use a seismograph measuring device to determine the strength of an earthquake. Engineers also want to be able to measure earthquakes so that they can help protect humans against the possible devastating effects of an earthquake.
The most common way of detecting and measuring earthquakes is a seismometer (also known as a seismograph). A seismometer is any device used to detect vibration in the Earth's surface. A simple seismometer consists of something suspended from springs that are allowed to swing as the Earth shakes. A pen attached to the device records all vibrations. Seismometers can be sensitive enough to detect earthquakes that people cannot even feel. Seismometers can detect a powerful earthquake anywhere in the world, but often seismometers are placed near fault lines to detect very small earthquakes. This information can help engineers predict when a large earthquake is due to occur. Faults are the boundaries between the tectonic plates that make up the surface of the Earth's crust. As the plates slide along each other, they slip and grind, causing earthquakes.
The Richter Scale is an numerical scale based on oscillations of the seismograph. Each number indicates 30 times stronger than the one before.
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The Modified Mercalli scales measures how people feel and react to the shaking of an earthquake.
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