Ratio of the Dead to Wounded (D/W) Indicators and Associated Factors in Major Earthquakes of America from 1960 to 2011
Summary of the Richter scale for the earthquakes, their effects, and the estimated frequency of occurrence .
Average earthquake effects
Average frequency of occurrence (estimated)
Microearthquakes. Not felt or felt rarely by sensitive people. Recorded by seismographs.
Continual/several million per year
Minor earthquakes. Felt slightly by some people. No damage to buildings.
>1 million per year
Minor earthquakes. Often felt by people, but very rarely causes damage. Shaking of indoor objects can be noticeable.
>100,000 per year
Light earthquakes. Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes none to minimal damage. Moderate to significant damage, very unlikely. Some objects may fall off shelves or be knocked over.
10,000–15,000 per year
Moderate earthquakes. Can cause damage of varying severity to poorly constructed buildings. At most, none to slight damage to all other buildings. Felt by everyone. Casualties range from none to a few.
1,000–1,500 per year
Strong earthquakes. Damage to a moderate number of well-built structures in populated areas. Earthquake-resistant structures survive with slight to moderate damage. Poorly designed structures receive moderate to severe damage. Felt in wider areas, up to hundreds of miles/kilometers from the epicenter. Strong to violent shaking in epicentral area. Death toll ranges from none to 25,000.
100–150 per year
Major earthquakes. Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from epicenter. Death toll ranges from none to 250,000.
10–20 per year
Great earthquakes. Major damage to buildings, structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake resistant buildings. Damaging in large areas. Felt in extremely large regions. Death toll ranges from 1,000 to 1 million.
1 per year
9.0 and greater
Near or at total destruction to severe damage or collapse to all buildings. Heavy damage and shaking extend to distant locations. Permanent changes in ground topography. Death toll usually over 50,000.