Maximum Spectral Energy Arrival Time of Rayleigh Waves for Accurate Epicenter Determination and Location Error Reduction

Maximum spectral energy MSE is defined as the most energetic signal in prescribed frequency and velocity windows characteristic to a seismic phase and is computed by means of the Fast Fourier Transform FFT and the Multiple Filter Analysis MFA. MSE arrival times for Rayleigh waves are computed in the period window 17 to 23 seconds and in the velocity window 2.8 to 3.2 kilometerssecond kmsec. These arrival times and a constant velocity model of 3.0 kmsec are used in a hypocenter computer program to evaluate location error, i.e., mislocation vector. Epicenter locations for selected nuclear explosions from the Nevada Test Site NTS are determined by the Rayleigh waves MSE arrival times. The same explosions are also located by the conventional P-wave first-break arrival times, listed in the International Seismic Center ISC Bulletin. Explosion selection is restrained by the availability of both arrival times from the same set of stations common to each explosion. This limited the study to only seven nuclear explosions each has 12 or more digital seismograms with corresponding P-wave first-break arrivals listed in the ISC Bulletin. The study is confined to NTS explosions, since for these there are published locations against which to compute the location errors. All such errors of epicenter location computed from MSE arrivals are less than those of epicenter locations from first-break arrivals. The location error for the seven explosions, calculated by the MSE arrivals, is half that calculated by the P-wave first-break arrivals.