Source scaling of Pn and Lg spectra and their ratios from explosions in central Asia: Implications for the identification of small seismic events at regional distances

[1] Multiple station recordings of Pn and Lg spectra from an m(b) = 6.6 nuclear explosion and several m(b) less than or equal to3.7 chemical explosions in central Asia are used to invert for source seismic moments (M-0), corner frequencies (f(c)), and path-variable Q models. A modified Mueller-Murphy source model fits the nuclear explosion well and fits the chemical explosions reasonably well, although Pn from chemical explosions are complicated by event-variable spectral fluctuations. New source spectral scalings are derived for underground explosions in a wide m(b) range between similar to3.7 and 6.6; they preserve features of the previous scalings, such as (1) larger Pn M-0 than Lg M-0, (2) quarter-root scaling between f(c) and M-0, and (3) higher Pn f(c) than Lg f(c) by factors of similar to4. A necessary and important consequence of the scalings is that the Pn/Lg spectral ratio grows rapidly in an intermediate frequency range between the f(c) of Pn and Lg. Since f(c) scales with event size, this frequency range shifts higher for smaller events. This magnitude dependence is directly confirmed using observed Pn/Lg ratios from the above explosions. It is also confirmed using Pn/Lg ratios observed at station WMQ using many m(b) similar to 6 and m(b) similar to 5 Soviet explosions. A procedure is proposed to account for then magnitude dependence of Pn/Lg ratios in the explosion identification.