TeleseismicLgof Semipalatinsk and Novaya Zemlya Nuclear Explosions Recorded by the GRF (Gräfenberg) Array: Comparison with RegionalLg(BRV) and their Potential for Accurate Yield Estimation

Abstract

Acomparison of regional and teleseismic log rms (root-mean-square)Lgamplitude measurements have been made for 14 underground nuclear explosions from the East Kazakh test site recorded both by the BRV (Borovoye) station in Kazakhstan and the GRF (Gräfenberg) array in Germany. The log rmsLgamplitudes observed at the BRV regional station at a distance of 690 km and at the teleseismic GRF array at a distance exceeding 4700 km show very similar relative values (standard deviation 0.048 magnitude units) for underground explosions of different sizes at the Shagan River test site. This result as well as the comparison of BRV rmsLgmagnitudes (which were calculated from the log rms amplitudes using an appropriate calibration) with magnitude determinations forPwaves of global seismic networks (standard deviation 0.054 magnitude units) point to a high precision in estimating the relative source sizes of explosions from Lg-based single station data. Similar results were also obtained by other investigators (PATTON, 1988; RINGDALet al.1992) usingLgdata from different stations at different distances.Additionally, GRF log rmsLgand P-coda amplitude measurements were made for a larger data set from Novaya Zemlya and East Kazakh explosions, which were supplemented withmb(Lg)amplitude measurements using a modified version of Nurru’s (1973, 1986a) method. From this test of the relative performance of the three different magnitude scales, it was found that theLgand P-coda based magnitudes performed equally well, whereas the modified Nuttlimb(Lg)magnitudes show greater scatter when compared to the worldwidembreference magnitudes. Whether this result indicates that the rms amplitude measurements are superior to the zero-to-peak amplitude measurement of a single cycle used for the modified Nuttli method, however, cannot be finally assessed, since the calculatedm b (Lg)magnitudes are only preliminary until appropriate attenuation corrections are available for the specific path to GRF.Key wordsSeismic yield estimationnuclear explosionsregional wavesrms coda magnitudes.