Magnitude

• magnitude: a measure of energy released by an earthquake

  • quantitative

• as magnitude increases, the earthquake tends to:

  • affect a broader region

  • shake for longer (damage more buildings, cause more harm)

Richter Magnitude Scale

• measures amplitude

  • amplitude: size of the waves on seismograph

• logarithmic scale: each degree of magnitude is 10x bigger waves

  • equates to 50x more energy per degree of magnitude

• not accurate for large, deep, or distant earthquakes

• no longer used

Moment Magnitude Scale

• the scale that’s now used

• measures strain energy along rupture surface (energy released)

• logarithmic scale: each degree of magnitude is 10x more energy released

• more accurate than richter

• most widely accepted and used by scientists

Intensity

• qualitative

• what we feel in an earthquake

• modified mercalli scale

• “I'“ is felt by very few people or not at all to “X” which is total destruction

Earthquake Intensity

• relates to ground motion’s effects on population and structures

• rely on “felt” reports

  • people provide location and their own intensity rating