

Derivative mappings: a nightmare imprint
as a slice through the cortex memory center: a Piranesian axonometric
projectin in the process of acceleration: spectral indications in
a red ascent.
Associative seismic measurement : PGA (peak acceleration)
is what is experienced by a particle on the ground. 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.
The mass on the rod behaves about like a simple
harmonic oscillator (SHO). If one "drives" the massrod
system at its base, using the seismic record, and assuming a certain
damping to the massrod system, one will get a record of the particle
motion which basically "feels" only the components of
ground motion with periods near the natural period of this SHO.
If we look at this particle seismic record we can identify the maximum
displacement. If we take the derivative (rate of change) of the
displacement record with respect to time we can get the velocity
record. The maximum velocity can likewise be determined. Similarly
for response acceleration (rate of change of velocity) also called
response spectral acceleration, or simply spectral acceleration,
SA (or Sa).
http://earthquake.usgs.gov/
research/hazmaps/haz101/faq/
parm04.php
Photographic sources:
Carrizo Plain, California Valley on
Elkhorn Road; ground debris. Background: details, Caltrans HQ, Los
Angeles. 











DATE: 2005
84 x 40 inches
213 x 101 cm
Chromogenic print, backmount, UV plexiglas facemount
Edition of 3 

