Seismic Calibration and Discrimination in Northeast Russia

In an effort to obtain ground truth (GT) classifications in support of nuclear explosion monitoring for continental regions of northeastern Russia, we relocated and assigned GT classifications to 118 seismic events reported in the International Seismological Centre (ISC) supplemented with previously unavailable local data. Of the relocated events, 26 events are classified as GT10. From these events, consistent patterns of residuals, essentially source-specific station corrections (SSSC’s), show upper mantle velocities are elevated under the Siberian platform and slower below the northern Sea of Okhotsk. To further improve calibration capabilities in northeast Russia, we have been analyzing data from a small network of digital seismic stations deployed in the Magadan region. The stations are located close to areas of both tectonic seismicity and active mining, thus record signals from both. We have been undertaking routine phase time picking and hypocenter determination of both local and near regional seismic events and confirmed/suspected mine explosions. Using waveforms of both tectonic events and mine blasts, we have begun the process of explosion discrimination using amplitude ratios of various Lg frequencies. Preliminary results indicate that the ratio Lg(4-8Hz)/Lg(0.75-1.5Hz) using peak amplitudes may not be sufficient to discriminate mining explosions from earthquakes in northeast Russia. Additional, more comprehensive research is underway. We have undertaken efforts to acquire improved ground truth data for both earthquakes and explosions. In January 2001 two moderate earthquakes occurred approximately 100 km west of Magadan. We deployed two temporary stations to investigate the aftershock sequences of both events. About 15 events were locate-able although several more were recorded. To obtain ground truth data for explosions, we have deployed temporary stations and recorded quarry blasts near Magadan, and are currently undertaking an experiment to record explosions at a coal mine several hundred kilometers north of Magadan.