A continuously recording seismic network was constructed in 1962 by the U.S. Geological Survey to locate epicenters and record incidence of bumps (bounces, rock bursts) that occur in the bituminous coal mines of the Book Cliffs coal field near Sunnyside, Utah. The coal is mined because of its value as coking coal, although those bumps may be a hazard to life and property.
Daily records of tremors caused by bumps for 1-3/4 years indicate that a seasonal pattern, as well as a daily pattern, exists for the number of bumps that occur in a given period. Maxima occur in May and June and in November and December. Marked increases at 5- to 9-day intervals are superimposed on these seasonal maxima. The largest bumps commonly occur during seasonal maxima when the rate of occurrence suddenly decreases and the amplitude of the individual bumps increases. Knowledge of this pattern may lead to prediction of general locations and periods of increased hazard from bumps. Experience to date has shown that prediction of precise times and locations of hazardous bumps is not possible, and may never be, primarily because even a small bump can be a hazard to life and property. Some bumps or bump sequences are actually composites, consisting of two or more discrete bumps a few tenths of a second to a few seconds apart.
