USGS Science Topics > Specific things by name
A measure of the magnitude of an earthquake based on the measured displacement of the earth at local sites. The original method was based on specific instrumentation but the general idea it describes is used in more modern estimates of earthquake magnitude.
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Ground shaking caused by the sudden release of accumulated strain by an abrupt shift of rock along a fracture in the earth or by volcanic or magmatic activity, or other sudden stress changes in the earth.
Repeated observation or sampling at a site, on a scheduled or event basis, for study and analysis. In general, this category excludes sampling programs in which materials are obtained in the field and brought back to a laboratory for study and analysis.