Discrimination between Earthquakes and Chemical Explosions in Eastern Russia Using Amplitude Ratios Obtained From Analog Records

Amplitude data from 237 earthquakes (1.5<mb<4.9, 10<Δ<916 km) and 247 chemical explosions (1.4<mb<3.9, 6<Δ<752 km), recorded by short period analog seismometers in Eastern Russia, was used to calculate 1164 amplitude phase ratios of five different types: Pg(h)/Sg(h), Pg(z)/Sg(z), Pg(h)/Sg(z), Pg(z)/Sg(h), and full vector, where h is the horizontal component and z is the vertical component. These amplitude ratios were analyzed in two regions of the Yakutia and Magadan regions of Eastern Russia as earthquake-explosion discriminants in four different ways: the raw phase ratio, the distance- corrected phase (DCP) ratio, the network-averaged phase (NAP) ratio, and the network-averaged distance- corrected phase (NADCP) ratio. Chemical explosions tended to show higher values than earthquakes for all types of amplitude ratios studied. The best earthquake-explosion discriminants found for both regions were Pg(h)/Sg(h), Pg(z)/Sg(h), and full vector NAP and NADCP ratios. These discriminants allowed for the classification of 86-92% of the ratios as being either earthquakes or explosions. Distinct separations were also found analyzing stations separately.