The size of an earthquake is given by it's magnitude which is often referredto as
On this scale the amplitude of shaking goes upby a factor of 10 for each unit on the scale.
Thus, at the same distancefrom the earthquake, the shaking will be 10 times as large
during a magnitude5 earthquake as during a magnitude 4 earthquake. The total amount of
energyreleased by the earthquake, however, goes up by a factor of 32.There are many
different ways that magnitude is measured from seismogramspartially because each method
only works over a limited range of magnitudes andwith different types of seismometers.
But all of the methods are designed to agree well over the range where theyoverlap.
The methods used in Northern California (NC) earthquake listings include:
local magnitude, the original scale defined by Richter and Gutenbergbased on the
maximum amplitude of the waves.
- coda magnitude, based on the duration of
- moment magnitude, based on inverting the waveforms for the moment
of theearthquake which is equal to the rigidity of the fault times the average amount
of slipon the fault times the amount of fault area that slipped.
The methods used in Southern California (SC) earthquake listings include:
empirically calibrated local magnitude based on readings from high-gain components
local magnitude based on synthetic Wood-Anderson response from low-gain components
local magnitude based on synthetic Wood-Anderson response from TerraScope stations