Explosion Contamination of the Seismicity Catalog in the Irkutsk, Buryat, and Chita Regions, Eastern Russia

Temporal analysis of seismicity catalogs can indicate possible contamination by anthropogenic events. Events associated with mining and construction tend to occur during the local day, while natural seismicity occurs at all hours. Examination of approximately 100,000 events listed in the published earthquake catalog (Materialy po Seismichnost Sibiri) for the Irkutsk and Chita Districts and the Buryat Republic in eastern Russia indicate significant explosion contamination. Areas of explosion contamination include: gold mining areas near Bodaibo, Bushulei, Ust Kansk, Karaftit, and Tsipikan; mica mining south of the Vitim River; and construction and industrial areas along the BAM, Trans-Manchurian, and Trans-Siberian railroads. Most of the gold mining is associated with placer deposits. Contamination is noted in copper and coal mining areas in northern Mongolia. Because of the large amount of natural seismicity in the rift basins northeast of Lake Baikal, explosion contamination associated with the construction of the BAM in those regions can not be distinguished. Explosions associated with coal and iron mining (e.g., near Cheremkhovo and Tulun) are not included in the seismicity catalog, indicating that these are successfully filtered by local operators. Exclusion of the explosion contamination indicates that the present-day activity is more concentrated along the Baikal rift zone and along the basins to the northeast, and less diffuse in the surrounding areas, than existing seismicity maps would indicate.