Statistical information on chemical explosions is needed in seismology, to evaluate the practical difficulties in identifying this very common type of seismic source from other seismic sources such as small earthquakes and small nuclear explosions.
We have obtained data on blasting activity from three different sources: (1) overview information from the U.S. Bureau of Mines (USBM) on the total amount of chemical explosives used in the United States during 1987, with breakdowns into different explosive types, and usage by different states; (2) overview information from the Mine Safety and Health Administration (MSHA) on the numbers of mines, of different types, in the United States; and (3) detailed information from a private company (Vibra-Tech Engineers, Inc.) on total shot size and size of charge per delay for 20,813 blasts carried out in 1987 at 532 locations.
Our procedure has been to extrapolate the detailed information contained in the 1987 Vibra-Tech data for a limited number of states and thus to obtain estimates for the whole country on numbers of shots and their size distribution. The extrapolation is constrained by the data from USBM (numbers of shots, sizes) and the MSHA (locations). Blasting activity does not fluctuate greatly from year to year and 1987 was representative of current practice.
We find that about 2.2 million metric tons of chemical explosive are used annually in the continental U.S., principally in mining for coal and metal ores. On a typical work day, there are roughly 30 explosions greater than 50 tons, including about one greater than 200 tons. There was one industrial explosion in 1987 at about 1400 tons. For shots between 1 ton and 100 tons, the cumulative distribution has a b-value near unity; that is, if N is the number of shots (per year) greater than or equal to W tons,
with b roughly equal to 1. This result is similar to the size distribution of earthquakes greater than magnitude mb,
Almost all chemical explosions above 1 ton are ripple-fired. The typical shot uses 20 to 50 separate delays.