Spectral method for estimating the quality of the medium from one source and two stations

Abstract

The method is suggested for estimating the quality (coefficient Q) of the medium from the longitudinal waves of the earthquakes in the regional zone (Q _P ). This method is based on analyzing the spectra of the P _n waves that are generated by one source and recorded at two stations; it does not require calculating the spectrum of the source and, thus, substantially simplifies the solution of the problem. This method is applicable if the propagation conditions of the signals between the source and each station are identical, i.e., the signal-to-station paths lie in the structurally and compositionally similar geological environments. Using the estimates of the Q _P -factor and the coefficient of seismic attenuation t*, calculated by the suggested method, we assessed the classification of the source-station paths as pertaining to the stable (S) or tectonic (T) regions for a number of earthquakes in Iran and South California and for the underground nuclear explosion of September 25, 2009 in North Korea. It is shown that the source-station path classification derived in the present study on the basis of the Q _P and t* parameters generally agree with the estimates derived in (Kedrov et al., 2010) from the attenuation coefficient b _Δ of the spectral parameters of recognition of the explosions and earthquakes. In the Appendix, it is demonstrated by the examples of several earthquakes in South California that prompt estimates of the Q _P parameter can also be calculated in the time domain from the amplitudes of the P _n waves at a frequency of 3 Hz, which are provided in the Bulletin of the International Data Center in Vienna.