Discrimination of Earthquakes and Explosions in Southern Russia Using Regional High-Frequency Data from IRIS/JSP Caucasus Network,

High frequency regional records from small earthquakes magnitude 4.5, and comparable magnitude chemical explosions, are analyzed to find a reliable seismic discriminant in the Northern Caucasus region in Southern Russia. About 130 digital, vertical-component seismograms recorded during 1992 by the IRISJSP North Caucasus Network operated by Lamont-Doherty Earth Observatory since 1991 in the distance ranges 10 to 250 km are used. Mean PgLg spectral ratios in the high frequency band 10 - 20 Hz are about 1 and 3 for earthquakes and explosions respectively, in the Northern Caucasus region, Southern Russia. These ratios are much higher than those observed in tectonically stable eastern U. S. where Kim et al. 1993 reported the mean PgLg ratios of 0.5 and 1.25 for earthquakes and explosions, respectively in the similar high frequency band. We find that the high-frequency PgLg spectral amplitude ratio in the frequency band 10-20 Hz is an adequate discriminant for classifying these events. A linear discriminant function analysis indicates that the PgLg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 7. The PgLg spectral amplitude ratio method we used is sufficiently reliable and robust that it can be used in discriminating chemical explosions especially numerous mining and quarry blasts from small regional earthquakes in the routine analysis of regional earthquake monitoring networks. We are evaluating the PLg spectral ratio and other potential discriminants using three component regional records. A key to our use of three component regional records fo discrimination analysis is correction of the free surface interaction, which allows direct comparison between the P-, SV- and SH-wave amplitudes and reveals clear radiation characteristics from the source.