Seismic discrimination of events at the Sangwon, North Korea, area using two-dimensional grid of Pg/Lg spectral ratios

This study presents the improvements of seismic event discrimination between explosions and earthquakes. We tried to find optimal frequency range based on 2D grids of Pg/Lg spectral amplitude ratios. Seismic data from CHNAR, BRDAR and KSGAR arrays located in the middle of Korean Peninsula are used for the discrimination of events occurred at the Sangwon, North Korea, area. We have analyzed seismograms of 122 explosions and 21 earthquakes to obtain a linear discriminant function that optimally discriminates explosions from earthquakes. Before calculating Pg/Lg spectral ratios, residual spectrum is computed by subtracting Brune's source spectrum from the observed spectrum. By using the residual spectrum, difference of spectral characteristics between explosion and earthquake populations could be emphasized. Two-dimensional spectral ratios were calculated in all combinations of Pg and Lg residual spectra in frequency band of 1 ~ 15Hz with the expectation of much greater differences of spectral amplitude between explosion and earthquake populations. We have determined the optimal frequency range where Pg/Lg spectral ratios are larger than a certain threshold in 2D grids. In the optimal frequency range, we obtain a linear discriminant function of each array. We calculated the compound discriminant function with the addition of the linear discriminant function at each array to improve the discriminant power. The new compound method enhanced the results in discrimination.