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Richter Magnitude Scale
Quantitative measurementMeasurement based off of
seismograph readings◦Amplitude of seismograph readings
determines sizeLogarithmic Scale
◦Each whole number represents a 10x increase in amplitude
◦Estimated to be about 31x increase in energy released
2.0 = Microquakes◦These are generally not felt by
people4.5 or greater can be felt all
around the worldLarge magnitude earthquakes
are 8.0 or greater (very infrequent)
Moment Magnitude ScaleQuantitative in measurementMeasurement of earthquakes in terms
of energy releasedTakes into account the actual
fault/ground movement◦Substance (rigidity)◦Average amount of slip◦Size of area that produced slip
Used by seismologists more frequently than Richter scale
Very similar readings to Richter Scale
Mercalli Intensity ScaleQualitative Observation
◦Used to quantify or put a number on a qualitative observation
Mercalli Intensity ScaleTakes into account
◦Earth’s surface◦Humans◦Objects of nature◦Man-made structures
Scale of 1 – 12, ◦1 = felt◦12 = total destruction
7.9 Mw, 7.7 Ms (The "traditional" magnitude of 8.3 for this earthquake was based on work by Richter [1958]. More recent research indicates that estimates in the range from 7.7 to 7.9 are more reliable.)
Great Alaska Earthquake 1964