Attenuation of Seismic Waves at Regional Distances

Abstract

Abstract : The coda-Q method was applied to determine the anelastic attenuation of 1-sec period Lg waves at NTS(Nevada Test Site), East Kazakh, the Indian subcontinent, and the South American continent. Mb(Lg) m sub b (Lg) versus explosion yield calibration curves are given for NTS explosions in hard rock and in alluvium. The NTS hard-rock calibration curve, when applied to explosions in other regions of the United States and in the French Sahara, gives realistic yield estimates. The technique also is applied to selected Soviet explosions in East Kazakh. M sub b (Lg) and M sub b (P) values were used to estimate the M sub b (P) bias between NTS and eastern North America. Assuming that explosions and earthquakes of the same M sub b (P) value excite Lg waves of equal amplitude, the P-wave magnitude bias between NTS and eastern North America. Assuming that explosions and earthquakes of the same M sub b (P) value excite Lg waves of equal amplitude, the P-wave magnitude bias between NTS and eastern North America is 0.31 magnitude units. A tentative value for the bias between NTS and Shagan River is 0.41 magnitude units, but this value may be changed. Frequency- dependence of crustal Q seems significant in regions of high Q, but are small or non-existent in regions of low Q values. Keywords include: Lg waves, Magnitude, Surface waves, Spectra, Nuclear explosions, and Seismic yield.