![]() This is very different in various parts of the nation. Attenuation is, basically, how far earthquakes waves are felt, and what the duration of the earthquakes is. Areas in red have a much higher likelihood than areas of white to be exceeded, for example.Īnother important thing is factored into plotting of the seismic-risk map is attenuation. Shaking is express as a percentage of g (g is the acceleration of a falling object due to gravity). Colors on this particular map show the levels of horizontal shaking that have a 2 % chance of being exceeded in a 50 year period. USGS National Seismic Hazard Map - These maps are based on current information about the rate at which earthquakes occur in different areas and on how far strong shaking extends from earthquake sources. (acceleration in g/10) These values are gathered from all parts of the nation to create a seismic-risk map, which is used by engineers and builders when designing earthquake resistant structures for different parts of the country. There are instruments called accelerographs that measure ground acceleration against the value of gravity. Consequently, engineers and designers rely a great deal on the measure of the peak ground acceleration, as compared to gravity, to determine how strong an earthquake force a new building may have to withstand. However, the mean and peak ground accelerations do have much to do with the intensity of damage a building may have to withstand. There are studies that show that much of the damage done in earthquakes is, perhaps, due rather to the velocity of the back and forth movements of the earth, than to the ground acceleration. It is approximately the same as a car traveling 100 meters from rest in just 4.5 seconds. Gravity is the rate at which an object falls when dropped from being at rest in a vacuum. In order to measure the acceleration of an earthquake, it must be measured against Gravity (or 1.0g). It is not unlike the feeling we have when a car takes off at high speed, or when we ride the roller coasters at Disneyland. In order to understand the Seismic Zoning method and how it pertains to the Steel Reinforced Concrete Dome, we must first understand what effective peak ground acceleration means and how it is measured against gravity.įirst let’s discuss what is meant by ground acceleration. ![]()
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