T. Wang1 , Y. Bian1
1Institute of Geophysics, China Earthquake Administration (CEA), Beijing, China
In this study we analyzed the ability to identify the first motion amplitude Pi P maximum amplitude Pm to S maximum amplitude Sm ratios, based on the small magnitude earthquakes and explosions that occurred in Huailai, Beijing. Considering the variations of amplitude attenuation, influenced by propagation paths, we selected a formula to study the attenuation characteristics of P, S amplitudes with epicenter distance, and obtained the result that the amplitudes of explosion attenuated faster than earthquakes. After attenuation correction, we calculated the amplitude ratios again and found that the correct identification rate of Pi/Sm amplitude ratios was improved from 84% to 98% and the Pm/Sm amplitude ratios was improved from 92% to 100%. This method has also been used to identify small magnitude events in North Korea. The correct identification rate of Pi/Sm amplitude ratios was improved from 77% to 93% and the Pm/Sm amplitude ratios were improved from 87% to 92%. In conclusion, the results show that as an additional criterion to maximum amplitude ratio, the initial amplitude ratio improves identification. After attenuation correction, the amplitude ratio criterion can be better applied to small magnitude earthquakes and explosions identification.