
Where earthquakes occur?: The danger of earthquakes changes significantly from place to place on the planet. Sources of most (but not all) earthquakes occupy well-formed belts, whereas between such belts the activity is low. The causes of such belt-like structure is explained by "plate tectonics": belts are boundary or contact areas between relatively strong plates. The following conclusions of plate tectonics are the most important
Most earthquakes occur along plate boundaries; Sizes of sources of earthquakes and the kinds of motion are different at different places of a plate; Some regularities have been revealed for interevent distances and time intervals between large earthquakes along plate boundaries, so that probable locations of impending events can be specified aforehand. back to index

How the power of earthquake is measured?: Two different measures of earthquake power are applied to earthquakes. The first is seismic or macroseismic intensity in degrees of 12-grade scale. In Russia the MSK-64 scale is an implicit standard. In North America and Europe, rather similar MM and EMS scales are used. The degree of 12-grade scale measures the earthquake effect or the intensity of shaking at a given place, so that the degree is maximum in epicentral area, that is around earthquake source, and decays with increased distance from the epicenter.

The second measure is magnitude known to most public through mass media as Richter scale. This quantity measures the total energy of seismic waves produced by an earthquake source. The larger is the magnitude of an earthquake, the larger is the size of the its source and the wider is the territory that may be devastated by seismic waves produced by this source.

In a rough analogy, compare an earthquake to an audio speaker. Then the intensity grade (of 12-degree scale) may be likened to the loudness of sound at a given place (measured in decibels), whereas magnitude (Richter scale) may be likened to the audio output of the speaker (measured in Watts).

Seismologists need both these measures. Please do not confuse them.
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What is the size of the source of earthquake?: . . .

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How I can protect myself in case of earthquake?: . . .

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