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A Study of Spectral Nulls and Scaling of P-Wave Spectra of Shagan River and Novaya Zemlya (USSR) Explosions. Volume 3
Final rept. 16 Apr 1989-15 Jul 1991
TELEDYNE GEOTECH ALEXANDRIA VA
Pagination or Media Count:
Spectral ratios PP-coda, PnLg, inter-shot ratios of P and Pn, and multichannel deconvolution are used to study spectral nulls on data from nearly 100 Shagan River and Novaya Zemlya explosions recorded at EKA, GBA, YKA, NORESS, MAJO, NORSAR, and WMQ. Spectra of P waves from Shagan River explosions show well-defined nulls due to cancellation by pP at the expected frequency of about 4 Hz for large m sub b approximately 6 shots, low-frequency nulls in teleseismic data related to both local geology and depth of burial, and distinct nulls at about 3 Hz in teleseismic data for large and small shots. Low-frequency P-coda appears to be due to the scattering of explosion-generated Rg. Comparison of observed data with synthetics suggests that observed P spectra vary more slowly with m sub b than predicted by commonly used scaling relationships. Analysis of data from 19 Novaya Zemlya explosions suggests that P-wave spectra of large shots have distinct spectral nulls at about 2.5-3.0 Hz, probably due to pP. PP-coda and inter-shot ratios at common receivers provide reliable methods for estimating spectral nulls. A comparison of synthetics with the observed data suggests the amplitude ratio pPP to be about 0.5 for large shots.
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