- What Exactly is an Earthquake?
- Why Do Earthquakes Happen?
- Earthquake Basics
- What Happens When an Earthquake Occurs?
- Earthquake Lesson
- What is an Earthquake?
- An Introduction to Earthquakes and Earthquake Hazards
- Overview of Earthquakes (PDF)
- What Causes Earthquakes?
- Plate Tectonics, the Cause of Earthquakes
- How are Volcanoes and Earthquakes Related?
Earthquake prediction includes not only the place and the time, but also the magnitude of the tremor. Scientists know that earthquakes occur along fault lines, so this makes it possible to predict the places where they will occur.
The size of the fault lines also makes it possible to have a rough idea about the intensity of earthquakes that will occur in specific areas. However, predicting the times these events might occur has not been possible to date. Another factor that contributes to the exact location of earthquakes is the way that energy tends to travels along a fault line, which can cause the overall size of an earthquake to be very large if the stress triggers tectonic plate movement along a long expanse of a fault line.
The Richter scale was developed in the 1930s and is most effective for large-scale earthquakes that are of moderate intensity. The Richter scale measures the maximum amplitude of seismic waves as they reach seismographs. This scale is expressed with a logarithmic scale.
Thus, an earthquake measuring 7.0 on the Richter scale would be 10 times larger than an earthquake that measures 6.0. Very large earthquakes that measure more than 7.0 on the Richter scale often cannot be measured precisely using this method because the energy released has a lower frequency but a broader range of power. For this reason, scientists now utilize more precise and advanced measurement methods.
Earthquakes are now measured in two separate ways based on the amount of energy released at the epicenter and the intensity of the earth shaking that occurs in specific locations. The moment magnitude scale measures the overall magnitude or size of the earthquake, and the modified Mercalli scale measures earthquake intensity.
For the moment magnitude scale, scientists use a formula to convert the energy released, as measured by a seismometer. Intensity measured by the modified Mercalli scale is assigned numbers between I and XII based on the amount of damage and reports received from eye witnesses. At level I, vibrations are extremely minor, possibly felt by only a few people. Level II involves vibrations on the upper floors of buildings with suspended objects swinging slightly. At level V, everyone feels vibrations. Objects fall off shelves and are overturned. Level VIII involves significant damage of even strong and well-designed structures. Brick buildings are often destroyed, and heavy objects become overturned. At the highest XII level, most structures are destroyed and objects become airborne.
By: Steven Moore