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

6.9 on Richter Scale

1906 San Francisco Earthquake

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

http://upload.wikimedia.org/wikipedia/commons/a/ae/Good_Friday_Earthquake_at_Turnagain_Arm.jpg

9.2 on Moment Magnitude ScaleDifficulty measuring on Richter

Scale◦Seismographs maxed out