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Course: American Museum of Natural History > Unit 4
Lesson 3: Earthquakes- Earthquakes 101
- How Are Earthquakes Measured?
- On Shaky Ground: Building a Safer Future in Haiti
- Science Bulletins: Tsunami Science—Reducing the Risk
- From Math to Maps
- Scientists at Work: San Andreas Fault
- Quiz: Earthquakes
- Exploration Questions: Earthquakes
- Answers to Exploration Questions: Earthquakes
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How Are Earthquakes Measured?
Due to the scale at which they take place, natural disasters can be challenging to measure. Consider earthquakes: you can’t ask how high an earthquake is, or quantify the weight of tectonic plates shifting against one another. What seismologists try to do instead is to measure the energy released by a quake.
Efforts to detect earthquakes stretch back thousands of years. In 132 CE, Chinese polymath Zhang Heng crafted what is thought to be the first seismic instrument, a bronze vase-shaped device with eight tubes, corresponding to direction points on a compass, protruding from it. When the vase detected an earthquake, the ball would drop from the appropriate tube into a container below, indicating the direction of the quake. Contemporary reports indicate this primitive seismoscope could detect quakes hundreds of miles away, though later attempts to replicate the device couldn’t reproduce this degree of accuracy.
Fast-forward to the 20th century. Most Americans are familiar with the Richter scale, which was developed by seismologist Charles Richter in 1935 at the California Institute of Technology. This scale is based on the largest shock wave recorded by a seismograph 100 km from the earthquake epicenter (the point on Earth’s surface directly above the rupture).
Initially devised only to compare the strength of moderate quakes along the San Andreas fault in southern California, the Richter scale was eventually generalized to measure earthquakes all over the world. The Richter scale is logarithmic, with each step up the scale marking a tenfold increase in quake strength—a 4.0 quake on the Richter scale, for instance, releases 10 times the energy of a 3.0 earthquake. The problem was that for large quakes—over 7.0 on the scale—the Richter scale was less reliable.
In 1979, as geologists developed more accurate techniques for measuring energy release, a new scale replaced the Richter: the moment magnitude, or MW scale, which seeks to measure the energy released by the earthquake. It’s also a logarithmic scale and comparable to Richter for small and medium quakes—a 5.0 on the Richter scale, for example, is also about a 5.0 MW quake—but better-suited to measuring large quakes.
No matter what scale is used, quakes are detected using devices called seismographs, which measure ground motion and produce images showing how these vibrations travel over time. The magnitude of a quake determines how it is classified by organizations such as the U.S. Geological Survey, from “micro” quakes—the smallest that can be felt by humans—to “great” quakes, which can cause devastation over huge areas.
Want to join the conversation?
- why can natural disasters be challenging to measure?(2 votes)
- why do we need to count earthquake(2 votes)
- What are the three zones around the globe where midt earthquakeoccur(1 vote)
- What year was it that people first try to detect earthquakes(1 vote)
- In my textbook they mentioned that GIS was used to detect earthquakes as well, but my teacher said it was not. I just want to know if GIS is or is not used.(1 vote)
- What day did the very first earthquake happen?(1 vote)
- Why do we need to measure earthquakes(0 votes)
- We need to measure earthquakes in order to caution people about the intensity of the earthquake.(4 votes)
- Why are they called micro quakes?(0 votes)
- because the earthquake is very tiny and micro means tiny.(2 votes)
- what would be the difference between 4.0 and 5.0(0 votes)
- 5.0 is ten times higer than 4.0 on the Richter scale(1 vote)
- Why is the Richter scale less reliable for earthquakes over 7.0? (4th paragraph)(0 votes)
- because the Richter scale can not musere earthquakes over 7.0(1 vote)