ON ESTIMATING THE AMOUNT OF BLASTS IN SEISMIC CATALOGS WITH SCHUSTERS METHOD

The events in a seismic catalog are represented by phasors of unit amplitude and with phase angles determined from the local time of occurrence of the events. A graphical display of the cumulative sum of these phasors reveals information about the distribution of the events in the catalog. The length of the resulting phasor walkout is used to test the catalog against the null hypothesis of random (Poissonian) seismicity. A statistically significant walkout in an otherwise complete catalog suggests nonrandom seismicity that could be due to the presence of misidentified blasts. We show how the length and orientation of the phasor walkout may be used in Schuster's method to estimate the amount of blast contamination in a catalog.