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HOME > PHOTO & PHOTOMONTAGE PHOTOMONTAGE FROM: CARRIZO-PARKFIELD DIARIES PROJECT
ACCELERATION SPECTRA previous next
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 mass-rod system at its base, using the seismic record, and assuming a certain damping to the mass-rod 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.
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DATE: 2005
84 x 40 inches
213 x 101 cm
Chromogenic print, backmount, UV plexiglas facemount

Edition of 3