THE EFFECTS OF DIGITIZATION ERRORS ON ANALYSIS OF STRONG-MOTION RECORDS AND THEIR ELIMINATION

Detailed analysis of digitization errors resulting from the processing of digitizing strong motion accelerograms is made in this paper. It shows that the digitization errors can be considered as a superposition of systematic errors introduced by the digitizing equipment and random noise errors produced mainly by operators. It also shows that the random noise is an ergodic stationary random process, the amplitudes of which are of Normal Gauss Distribution, and the long period components of their frequency content are apparently predominant. It will, thus, give a serious effect on the double integrated displacement from a digitized accelerogram containing these errors. But further studies indicate that random digitized noise displacemets are mainly distributed in the range of periods longer than 25 second and give relatively small values up to a period of 25 second for the accelerogram, the typical recording speed of which is 1 cm/ sec. Accordingly, a background of random noise is obtained and most parts of such noise could be filtered out from the digitized accelerograms by using of the digital filtering. A typical filtered accelerogram and its double integrated displacements are given as an example and a comparison with the unfiltered accelerogram and its respective displacements is also made.