Measuring Earthquake Size

• Two main ways to describe EQ size
  • Severity of effects: intensity
    • indicator of degree of shaking at a given locale, based on movement and damage.
  • Ground Motion: magnitude
    • estimate of the amount of energy released by the earthquake
• Let’s talk intensity first

Modified Mercalli Intensity, MMI Scale:

• developed about 1930 (CalTech)
• based on effects on California buildings
• range= I(not felt) to XII (Catastrophic)
• diminishes with distance
• affected by rocks, soils, building types, etc.

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