FAQs - What do the ground-motion parameters on these maps mean?
- What is "Peak Acceleration" or "Peak Ground Acceleration" (PGA)?
- What is "% g"?
- 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?
- What is "probability of exceedance" or PE?
- What is "spectral acceleration" or SA?
- What is percent damping?
- Your 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?
- 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)?
- 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?
- 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? See the next FAQ.
