Understanding Seismic Magnitude
The magnitude of an earthquake is a logarithmic measure of its size. This means that for every whole number increase on the scale, the amplitude of the shaking grows 10 times larger, and the energy released increases roughly 32 times.
For example, a magnitude 7.0 earthquake releases about 1,000 times more energy than a magnitude 5.0 earthquake.
What Do The Numbers Mean?
- 2.5 or less: Usually not felt, but recorded by seismographs.
- 2.5 to 5.4: Often felt, but typically causes only minor damage.
- 5.5 to 6.0: Slight damage to buildings and other structures.
- 6.1 to 6.9: May cause a lot of damage in very populated areas.
- 7.0 to 7.9: Major earthquake. Serious damage.
- 8.0 or greater: Great earthquake. Can totally destroy communities near the epicenter.
Safety: Drop, Cover, and Hold On
If you feel shaking, do not run outside. Most injuries occur from falling debris.
Drop to your hands and knees. This prevents you from being knocked over.
Cover your head and neck with your arms. Crawl under a sturdy table if possible.
Hold on to your shelter until the shaking stops.
Frequently Asked Questions
Can earthquakes be predicted? ▼
No. Neither the USGS nor any other scientists have ever predicted a major earthquake. We can calculate probability (forecasts) over years, but we cannot predict the exact time, date, or location of a quake.
What is the "Ring of Fire"? ▼
The Ring of Fire is a horseshoe-shaped belt around the Pacific Ocean where about 90% of the world's earthquakes occur. It is home to over 450 volcanoes and is defined by the movement of several major tectonic plates.