Earthquakes: Magnitude and Intensity
Magnitude
- magnitude: a measure of energy released by an earthquake
- 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