Correction of P/S Amplitude Ratios for Low-Magnitude Seismic Events Based on Bayesian Kriging Method

Abstract

ABSTRACT Classification of low-magnitude seismic events is a challenging issue for the Comprehensive Nuclear-Test-Ban Treaty. Path correction of the P/S amplitude ratio is the key to identifying earthquakes and explosions. In this article, the Bayesian Kriging interpolation method is used to conduct the path correction of P/S amplitude ratios and recognition of low-magnitude seismic events. Based on a total of 5677 small earthquakes and 1769 explosions in Beijing and its adjacent areas, the Bayesian Kriging method is used to establish the path correction surface and uncertainty surface of Pg/Lg amplitude ratios measured within different frequency bands at five seismic stations, and path correction of amplitude ratios is conducted for all events. The results show that the correction surface is consistent with the observed amplitude ratios, which can reflect the differences in their propagation paths to a certain extent. The root mean square variation of the amplitude ratio is reduced by a maximum of 30% and the misclassification probability is reduced by a maximum of 8.5% after the Kriging correction. The high-frequency Pg/Lg amplitude ratios can effectively classify low-magnitude events, and the misclassification probability at each station is less than 15% and 10% based on high-frequency Pg/Lg of >7 and >9  Hz, respectively. Of the five stations, BJT (Baijiatuan, Beijing) has the best recognition, with the misclassification probability being lower than 5% after Kriging correction based on high-frequency Pg/Lg (>9  Hz). The classification ability of high-frequency amplitude ratios (>15  Hz) is weakened due to high-frequency noises. Bayesian Kriging correction can reduce the variance in the amplitude ratio of low-magnitude seismic events and hence effectively improve the ability to classify small-magnitude events, which has an important reference value for regional seismic monitoring and identification.