Katana VentraIP

Seismic magnitude scales

Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary based on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.

of distant earthquakes (over ~600 km) because of attenuation of the S-waves,

of deep earthquakes because the surface waves are smaller, and

of strong earthquakes (over M ~7) because they do not take into account the duration of shaking.

Magnitude of completeness

Epicentral distance

– Pacific Tsunami Warning Center

Perspective: a graphical comparison of earthquake energy release

Providing near-real-time maps of ground motion and shaking intensity following significant earthquakes.

USGS ShakeMap