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- A certain ground motion has an x percent probability of being exceeded in Y years. What is the probability, w that that same ground motion is exceeded in Z years?
Please see this PDF file for instructions.... - How do I get hazards zone maps for locations outside of the US?
We know of no current "zone" designations for sites outside of the United States.For locations outside the United State for which seismic design is required for military facilities, there exists a standard based on probabilistic spectral ordinates in the m... - How do I use the National Seismic Hazard Maps?
The maps come in three different probability levels and four different ground motion parameters, peak acceleration and spectral acceleration at 0.2, 0.3, and 1.0 sec. (These values are mapped for a given geologic site condition. Other site conditions may i... - I am trying to calculate the ground motion effect for a certain location in California. I obtained the design spectrum acceleration from your site, but I would like to identify the soil type of this location, how can I reach it?
You can't find that information at our site. We don't know any site that has a map of site conditions by National Earthquake Hazard Reduction Program (NEHRP) Building Code category. There is a map of some kind of generalized site condition created... - If I were to use an accelerometer to measure seismic events, how could I convert the acceleration data (in g's) to the magnitude numbers you folks use?
You can't convert acceleration to magnitude. Magnitude is a measure of the size of the earthquake. Peak ground acceleration (pga) in percent g is a measure of the ground motion, which decreases, the further you are from the earthquake. Alternatively, ... - What is "% g"?
When acceleration acts on a physical body, the body experiences the acceleration as a force. The force we are most experienced with is the force of gravity, which caused us to have weight. The units of acceleration of the map are measured in terms of g, th... - What is "Peak Acceleration" or "Peak Ground Acceleration" (PGA)?
1. What is "acceleration"? When you push on the gas pedal in your car, you experience the increase in velocity as a force pushing you back into your seat. Technically, then, acceleration is the rate of increase in velocity, that is, how much the velocity ... - What is "probability of exceedance" or PE?
For any given site on the map, the computer calculates the ground motion effect (peak acceleration) at the site for all the earthquake locations and magnitudes believed possible in the vicinity of the site. Each of these magnitude-location pairs is believe... - What is "spectral acceleration" or SA?
PGA (peak acceleration) is what is experienced by a particle on the ground, and SA is approximately what is experienced by a building, as modeled by a particle mass on a massless vertical rod having the same natural period of vibration as the building. Th... - What is a seismic zone, or seismic hazard zone?
A seismic zone could be one of three things: A region on a map in which a common level of seismic design is required. This concept is becoming obsolete. An area of seismicity probably sharing a common cause. Example: "The New Madrid Seismic Zone." A r... - What is percent damping?
In our question about response acceleration, we used a simple physical modela particle mass on a mass-less vertical rodto explain natural period. For this ideal model, if the mass is very briefly set into motion, the system will remain in oscillation indef... - What is the likelihood of a large earthquake at location X?
Our analyses do not answer your question as stated, "probability of large earthquake at a location," but in a more suitable manner for safety. Danger comes, not only from large earthquakes AT a location, but also large earthquakes further away, and close, ... - What is the relationship between peak ground acceleration PGA and "effective peak acceleration," Aa, or between peak ground velocity and "effective peak velocity," Av, as these parameters appear on building code maps?
Aa and Av have no clear physical definition, as such. Rather, they are building code constructs, adopted by the staff that produced the Applied Technology Council (1978) (ATC-3) seismic provisions. Maps for Aa and Av were derived by ATC project staff from ... - What is the siesmic zone number for Federal Site Z?
Zone numbers are no longer applicable to federally operated, federally funded, or federally insured structures. Since about 1980, the federal building code maps have been based on two ground-motion contour maps, one relating to long period ground motions, ... - What seismic zone is location X in?
We cannot give you this information. Since 1976, our hazard maps have not used this format. The only remaining model building code for the US which uses zone number is the UBC.... - Where can I find seismic zone maps with 0, 1, 2, 3, 4?
Building code maps using numbered zones, 0, 1, 2, 3, 4, are practically obsolete. 1969 was the last year such a map was put out by this staff. The 1997 Uniform Building Code (UBC) (published in California) is the only building code that still uses such zon... - Your map values show ground motions that have a probability of being exceeded in 50 years of 10, 5 and 2 percent. What is the probability of their being exceeded in one year (the annual probability of exceedance)?
Let r = 0.10, 0.05, or 0.02, respectively. The approximate annual probability of exceedance is the ratio, r*/50, where r* = r(1+0.5r). (To get the annual probability in percent, multiply by 100.) The inverse of the annual probability of exceedance is known... - Your seismic hazard map is for ground motions having a 2% probability of exceedance in 50 years.
Are those values the same as those for 10% in 250?
Yes, basically. This conclusion will be illustrated by using an approximate rule-of-thumb for calculating Return Period (RP). A typical seismic hazard map may have the title, "Ground motions having 90 percent probability of not being exceeded in 50 years....