By identifying the greatest hazards, we can set priorities for using our limited resources most effectively to reduce them. The choice is ours. Strength decreases rapidly with distance from the earthquake. The strong shaking along the fault segment that slips during an earthquake becomes half as strong at a distance of 8 miles, a quarter as strong at a distance of 17 miles, an eighth as strong at a distance of 30 miles, and a sixteenth as strong at a distance of 50 miles. Length of shaking.
Length depends on how the fault breaks during the earthquake.
The maximum shaking during the Loma Prieta earthquake lasted only 10 to 15 seconds. During other magnitude 7 earthquakes in the Bay Area, the shaking may last 30 to 40 seconds. The longer buildings shake, the greater the damage. Type of soil. Shaking is increased in soft, thick, wet soils.