Signal-to-Noise Ratio Improvement by Time-Shifting and Summing Lasa Seismograms

摘要

Short-period LASA seismograms of nineteen earthquakes were prefiltered, time-shifted, and summed by digital computer to determine for each event the P-wave signal-to-noise ratio gain relative to the average input. Compared to the mean, the 'signal' amplitude, i.e., half the maximum peak-to-trough deflection in the P signature, was suppressed on each final trace about 3 db, whereas the root-mean-square level was lowered 18 to 21 db. The prefiltering and signal alignment procedures, however, significantly reduced the first-motion amplitude of unfiltered data. The average signal-to-noise ratio for each event was improved 15 to 18 db by summing all LASA traces. Approximately 5 db of the improvement is attributed to the modified time shifts resulting from the use of predetermined average travel-time anomalies. (Author)