What is moment magnitude?
Quick Answer
Moment magnitude is the modern scale scientists use to measure earthquake size based on the amount of energy released. It is the standard measure for large earthquakes today.
The Full Story
Moment magnitude, written as Mw, is calculated from the seismic moment of an earthquake, which depends on how much a fault slipped, how large the rupture was, and how rigid the rocks are. Unlike older magnitude methods, it works well for both moderate and giant earthquakes. This is why major events such as the 2011 Tōhoku earthquake are reported using moment magnitude, in that case about 9.0. It gives a more physically meaningful measure of earthquake size than the older local magnitude approach.
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