Richter Magnitude Scale Quantitative measurement Measurement based off of seismograph readings ◦ Amplitude of seismograph readings determines size Logarithmic 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 people 4.5 or greater can be felt all around the world Large magnitude earthquakes are 8.0 or greater (very infrequent)

Moment Magnitude Scale Quantitative in measurement Measurement of earthquakes in terms of energy released Takes 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 Scale Qualitative Observation ◦ Used to quantify or put a number on a qualitative observation

Mercalli Intensity Scale Takes 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

9.2 on Moment Magnitude Scale Difficulty measuring on Richter Scale ◦ Seismographs maxed out