| abstract |
A formation is blasted with one or more arrays of elongated, chemical, explosive charges so as to produce relatively low levels of ground vibration. The orientation and velocity of propagation of explosion in each charge and the velocity of propagation of vibration in the formation are such that, at a selected outlying location, the onset of vibration from explosion of the first negligably small increment of the charge arrives a finite time before that from explosion of the last negligably small increment. The charges of each array are fired in accurately-timed sequence, with the times between initiations chosen so that, at the outlying location, the onset of vibration from explosion of the last small increment of each charge, except the last charge, arrives a negligably small increment of time before the onset of vibration from explosion of the first small increment of the succeeding charge. All arrays ape designed to give equal times between onsets of vibration from the first and last charge increments to explode. Arrays are initiated in accurately-timed succession such that, at the outlying location, the onsets of vibration from the first small increment of charge to detonate in each of the arrays arrive separately at time intervals approximately equal to zero to four complete periods of a major Fourier component of the vibration from a single array, plus one period divided by the number of arrays. Explosives having low rates of propagation are preferred. |