Earthquake

Earthquakes are the vibrations or shaking created when large blocks of the earth’s crust move against one another. The break between these blocks is a “fault.” Most earthquakes in the earth’s crust occur from movement on faults. Less frequently, some earthquakes are caused by volcanic or magmatic activity (Colorado Natural Hazards Mitigation Plan, 2013, p. 3-153).

Magnitude and intensity are terms used to describe seismic activity. Magnitude (M) is a measure of the total energy released. Each earthquake has one magnitude. Intensity (I) is used to describe the effects of the earthquake at a particular place. Intensity differs throughout the area. The Richter Scale is commonly used to measure magnitude, and the Modified Mercalli Intensity Scale (MMI) measures intensity.

The most intense shaking experienced during earthquakes generally occurs near the rupturing fault and decreases with distance away from the fault. In a single earthquake, however, the shaking at one site can easily be 10 times stronger than at another site, even when their distance from the ruptured fault is the same.