Seismic moment is a quantity used by earthquake seismologists to measure the size of an earthquake. The scalar seismic moment is defined by the equation, where
- is the shear modulus of the rocks involved in the earthquake (in dyn/cm2)
- is the area of the rupture along the geologic fault where the earthquake occurred (in cm2), and
- is the average displacement on (in cm).
thus has dimensions of energy, measured in dyne centimeters.
The seismic moment of an earthquake is typically estimated using whatever information is available to constrain its factors. For modern earthquakes, moment is usually estimated from ground motion recordings of earthquakes known as seismograms. For earthquakes that occurred in times before modern instruments were available, moment may be estimated from geologic estimates of the size of the fault rupture and the displacement.
Seismic moment is the basis of the moment magnitude scale introduced by Hiroo Kanamori, which is often used to compare the size of different earthquakes and is especially useful for comparing the sizes of especially large (great) earthquakes.
Famous quotes containing the words seismic and/or moment:
“Most near, most dear, most loved and most far,
Under the window where I often found her
Sitting as huge as Asia, seismic with laughter,”
—George Barker (b. 1913)
“Shall we never have done with that cliché, so stupid that it could only be human, about the sympathy of animals for man when he is unhappy? Animals love happiness almost as much as we do. A fit of crying disturbs them, they’ll sometimes imitate sobbing, and for a moment they’ll reflect our sadness. But they flee unhappiness as they flee fever, and I believe that in the long run they are capable of boycotting it.”
—Colette [Sidonie Gabrielle Colette] (1873–1954)