Multi-phase stacked P/S-type spectral ratio at a single station for discrimination between earthquake and explosion sources

The seismograms from natural earthquakes and explosions are significantly different. Explosions tend to generate strong compressional waves and weak shear waves. In contrast, natural earthquakes are primarily driven by dislocation sources, resulting in strong shear waves and relatively weak compressional waves. The differences in energy radiations between P- and S-waves can be used to identify explosions and natural earthquakes. On October 9, 2006, D.P.R. Korea conducted the first underground nuclear test. When using the spectral ratio Pg/Lg from the vertical component seismic record at the Mudanjiang (MDJ) station to identify source types, it can discriminate between explosion source attributes at frequencies between 9 and 15 Hz. Due to the random effects in the data, using single-station records for discrimination may result in a narrow frequency band and a higher misdetection rate, especially at lower frequencies and for noisy data. Recent investigations have demonstrated that stacking spectral ratios from multiple stations in a regional network can reduce data fluctuations at individual stations, expand the useful frequency band, and successfully identify D.P.R. Korea nuclear explosions within earthquake populations within frequencies of 2 ~ 15 Hz. The above situation inspired us to consider stacking P/S type spectral ratios, such as Pg/Lg, Pn/Lg, and Pn/Sn, observed at a single station, for effectively identifying earthquakes and explosions. We designed a method for stacking different types of spectral ratios at a single station. The new method achieved good identification results and demonstrated that the D.P.R. Korea underground nuclear tests can be discriminated from earthquake populations within frequencies of 2 ~ 15 Hz. The new method is suitable for situations where only a single station is available in remote areas. Also, we calculated and stacked the spectral ratio Pg/Sn.