A Comparison of Teleseismic P Wave Amplitudes and Spectra Observed at Selected Basin and Range Sites and in Eastern North America. Phase 1. Volume 2

Abstract

Abstract : Three Seismic Data Collection System (SDCS) stations were deployed at the Nevada Test Site (NTS) and two in the Eastern United States (EUS) to measure magnitude residuals and spectral differences between NTS and EUS stations. The deployment was intended to determine the degree of anelastic attenuation under NTS. At the Climax Stock (OB2NV) station, the teleseismic body-wave magnitudes are .17 magnitude units (m.u.) lower than at the EUS stations. The magnitudes at the two Pahute Mesa sites are about .2 m.u. higher than at OB2NV, a difference that can be accounted for by amplification of low velocity volcanics under Pahute Mesa. Thus local geology must be taken into account in order to evaluate the attenuation under a given site using amplitude data. This correction shows that with respect to corrected amplitude levels OB2NV is equivalent to Pahute Mesa stations. At all NTS sites the higher frequency content of P waves is significantly less than in the EUS. Available data suggests an attenuation effect of about .2 m.u. under NTS. Measurements at a few other Western United States (WUS) sites, including the site of the SHOAL explosion, yield similar figures. These results confirm that body-waves suffer considerable anelastic losses traversing the mantle under the WUS, including the NTS sites. (Author)