A study of high-frequency errors present in digitized accelerograms and an analysis of the distribution of unequally spaced, hand-digitized data indicates that the Fourier content of digitized accelerogram. data may be accurate up to about 25 cps.Two methods for accelerometer instrument correction are described: (1) a direct numerical differentiation of recorded accelerograms from which high-frequency digitization errors have been filtered out and (2) an ideal "mathematical accelerometer" with a natural frequency significantly higher than the natural frequency of the recording instrument. Although both methods give good results, the first one is recommended for the standard use.
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