On-site seismic yield (OSSY) estimates for BRISTOL based on nuclear to chemical explosion spectral ratios and yield scaling

Abstract

We have computed a seismic yield estimate for the nuclear explosion BRISTOL by scaling near-source seismic recordings of BRISTOL with recordings from chemical explosions. Path and near-source coupling effects were accounted for by modeling ratios of the spectra of BRISTOL and chemical explosions recorded at identical locations and detonated in nearly the same locations. We estimated BRISTOL's yield, corner frequency, and overshoot by minimizing the difference between observed spectral ratios and model spectral ratios assuming yield scaling. Based on an average of spectral ratios at six stations, and assuming an average, gas-filled porosity of 4% in the vicinity of BRISTOL's working point, we obtained a yield of 10 kt with an interstation uncertainty corresponding to an increase or decrease by a factor of 1.7. This uncertainty could probably be reduced by using sensors with better low-frequency response and chemical explosions that generated larger signal to noise ratios (SNR). This yield estimate is in good agreement with a yield estimate obtained using regional Lg waves of Y = 11. We also find a corner frequency of 2.5 Hz and no evidence of overshoot in the seismic source function. Measurements such as these help improve our understanding of explosion sources and may be important for verification of threshold and low-yield nuclear testing treaties because they are less intrusive and potentially less expensive than existing on-site methods such as Continuous Reflectometry for Radius versus Time Experiment (CORRTEX). They are also applicable to explosions of all sizes.