Measuring Ground Motion

Question 1

what is RMS acceleration, and what is it sensitive to?

Answer 1

arms = sqrt{1/Td[ integral 0 - Td of a(t)^2 dt]} sensitive to the duration adopted

Question 2

what is the Arias Intensity?

Answer 2

pi/2g integral from 0 - Td of a(t)^2 dt, unites of velocity

Question 3

what is Housner Intensity a function of?

Answer 3

Damping, period

Question 4

what is a fourier amplitude spectrum?

Answer 4

shows the variation of amplitude with frequency, expresses the frequency content of the ground motion.

Question 5

what is a fourier phase spectrum?

Answer 5

shows the variation of phase with frequency, eg when the peaks of harmonic motion occur

Question 6

what are some key characteristics of a fourier amplitude spectrum?

Answer 6

the higher the magnitude, the higher the peak/plateau region
plateau is longer for larger magnitudes
larger magnitudes have their plateau in the lower frequency regions
the plateau region is inversely proportional to the cube root of the seismic moment, therefore higher magnitude = higher seismic moment