Knowra Earthquake magnitude Earthquake magnitude Earthquake magnitude is a logarithmic measure of an earthquake’s size, estimated from seismic waves or other evidence. Different magnitude scales use different measurements but are calibrated to describe comparable event sizes.
Moment magnitude scale : A logarithmic earthquake magnitude scale based on seismic moment, now used for most significant earthquakes. It estimates size from fault area, slip, and rock rigidity, avoiding saturation for very large earthquakes.
Modified Mercalli intensity scale : A twelve-level scale describing earthquake effects and shaking severity at a particular location. Unlike magnitude, intensity varies from place to place for the same earthquake.
Earthquake early warning system : A system that detects an earthquake’s initial waves and sends alerts before stronger shaking arrives. Rapid magnitude estimates help predict the severity and reach of impending shaking.
Magnitude saturation : The failure of some magnitude scales to increase adequately as earthquake size grows. It explains why older amplitude-based scales compress the sizes of the largest earthquakes.
Richter magnitude scale : A local magnitude scale developed by Charles Richter for earthquakes in Southern California. Its familiar name describes one early method based on measured seismic-wave amplitudes.
Local magnitude : An earthquake magnitude estimated from the amplitude of nearby seismic waves, with corrections for distance. It is the scale commonly called Richter magnitude, but it can underestimate very large events.
Seismic hazard : The probability and expected severity of earthquake ground motion at a location over a specified period. Magnitude distributions help estimate how often damaging earthquakes may occur.
Earthquake magnitude uncertainty : The error and variability in an earthquake’s estimated magnitude due to data and method limitations. Different stations, corrections, and scale choices can produce distinct estimates for one event.
Seismic moment : A measure of an earthquake’s physical size, calculated from fault area, average slip, and rock rigidity. Moment magnitude converts this source measure into a logarithmic magnitude value.
Body-wave magnitude : A magnitude estimated from the amplitude of seismic body waves, especially short-period compressional waves. Its readings saturate for large earthquakes, so it can rank their sizes poorly.
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