Estimates of Seismic Detection Capability in the Soviet Union Based on NORESS Observations

摘要

The detection capability of the NORESS seismic array is estimated, and the results are used to estimate the detection threshold of a network including NORESS-type stations in the Soviet Union. First, the frequency-dependent attenuation of Pn and Lg at NORESS is estimated by inverting single-channel spectra from 186 events at ranges between 200-1400 km with magnitudes between 1.1 and 4.8. The Pn spectra are inverted between 1-15 Hz and the Lg spectra between 1-7 Hz for both seismic moment and apparent attenuation. The result is a simple parameterization of the source and range dependence of regional Pn and Lg spectra. However, signal detection at NORESS is determined from time domain filtered beams, so a parameterization of single-channel spectra is not sufficient to determine detection capability. Therefore, we determine the relationship between the spectral amplitudes used in the inversion and the time domain amplitudes used in signal detection. We find that the temporal signal-to-noise ratio for Pn on a filtered beam can be expressed as a product of the single-channel spectral SNR and terms specific to the NORESS array configuration and beamforming. This factorization allows us to determine NORESS detection capability from our spectral parameterization, and to predict the Pn detection capability for other regions and other station configurations. We determine an empirical relationship for Lg detectability based on observed temporal amplitudes, noting that the results cannot be easily extrapolated to other areas with different attenuation. (EDC)