Figure 13. (a) Segment of the 20 March aftershock record at Sylmar Converter Station-East, free-field, scanned from film. (b) An enlarged portion of the vertical trace after repeated Xeroxing, showing associated distortions. Also the "old" and "new" versions of digitized data are shown. The differences may be due to high contrast preprocessing of the scanned image in producing the "old" version.